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Troubleshooting EIGRP Neighbor Relationships

1. Routing Table Snapshot of Router A After the Configuration Change to Verify the Fix Router A show ip route 192 168 1 0 24 is directly connected Serial 0 192 168 2 0 24 is directly connected Serial 1 192 168 3 0 24 is directly connected Ethernet 0 172 16 81 1 24 is directly connected Loopback 0 172 16 99 0 24 90 409600 via 192 168 1 1 Serial 0 172 16 97 0 24 90 409600 via 192 168 1 1 Serial 0 172 16 79 0 24 90 409600 via 192 168 1 1 Serial 0 172 16 70 0 24 90 409600 via 192 168 1 1 Serial 0 172 16 103 0 24 90 409600 via 192 168 1 1 Serial 172 16 76 0 24 90 409600 via 192 168 1 1 Serial 172 16 80 0 20 is a summary 00 03 24 Null 172 16 98 0 24 90 409600 via 192 168 1 1 Serial OR o 0O 0 0O 0C ooo EIGRP Summarization Route Problem Cause Too Much Summarization Another EIGRP summarization route problem stems from when the summary route covers more subnetworks than exist Figure 7 31 shows the network diagram to refer to for this case study As shown in Figure 7 31 Router B is connected to the network cloud with network of 172 16 1 0 24 through 172 16 15 0 24 Router B is summarizing those networks into one big summary route of 172 16 0 0 16 and sending it to Router A Router A is connected to the core network and Router A is sending Router B a default route of 0 0 0 0 0 0 0 0 The problem arises when a device in the core network tries to reach a network of 172 16 40 0 24 which is nonexist
2. EIGRP resets the neighbor relationship because of a stuck in active condition The error message is DUAL 3 SIA Route network mask stuck in active state in IP EIGRP AS Cleaning up This section discusses the method of troubleshooting the EIGRP stuck in active error Reviewing the EIGRP DUAL Process To resolve an EIGRP stuck in active error you need to understand the DUAL process in EIGRP Refer to Chapter 6 for thorough coverage of the DUAL process although it is reviewed here as well EIGRP is an advanced distance vector protocol it doesn t have LSA flooding like OSPF or a link state protocol to tell the protocol the overall view of the network EIGRP relies only on its neighbors for information on network reachability and availability EIGRP keeps a list of backup routes called feasible successors When the primary route is not avail able EIGRP immediately uses the feasible successor as the backup route This shortens convergence time Now if the primary route is gone and no feasible successor is available the route is in active state The only way for EIGRP to converge quickly is to query its neighbors about the unavailable route If the neighbor doesn t know the status of the route the neighbor asks its neighbors and so on until the edge of the network is reached The query stops if one of the following occurs All queries are answered from all the neighbors The end of network is reached The lost route is un
3. The network administrator changed the K values of RTR B to all 1s from K1 to K4 while RTR A retains the default value of K1 and K3 to be 1 In this example RTR A and RTR B will not form EIGRP neighbor relationship because the K values don t match Example 7 5 shows the configu ration for RTR B Example 7 5 Configuration for RTR B in Figure 7 8 RTR B router eigrp 1 network xxxx metric weights 011110 RTR B s configuration includes the extra metric weights command The first number is the type of service ToS number which because it s not supported gets a value of 0 The five numbers after the ToS are the K1 through K5 values Troubleshooting this problem requires careful scrutiny of the router s configuration The solu tion for this problem is to change all the K values to be the same on all the neighboring routers In this example in Router A changing the K values to match the K value of Router B will solve the problem as demonstrated in Example 7 6 Example 7 6 Configuring the K Values on Router A to Match Router B RTR A router eigrp 1 network xxxx metric weights 011110 Troubleshooting EIGRP Neighbor Relationships 239 EIGRP Neighbor Problem Cause Mismatched AS Number Figure 7 9 Example 7 7 Example 7 8 EIGRP won t form any neighbor relationships with neighbors in different autonomous systems If the AS numbers are mismatched no adjacency is formed This problem is usually caus
4. eigrp 1 distance 90 metric 2195456 type internal Redistributing via eigrp 1 Last update from 192 168 1 2 on Serial 00 16 24 ago Routing Descriptor Blocks 192 168 1 2 from 192 168 1 2 00 16 24 ago via Serialo Route metric is 2195456 traffic share count is 1 Total delay is 21000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 Troubleshooting EIGRP Route Installation 267 EIGRP Is Not Installing Routes Cause Higher Administrative Distance Refer to the network topology in Figure 7 25 Another variation of a similar problem can happen if network cloud Y sends external EIGRP routes of 150 150 0 0 16 to Router B and Router B is running RIP and EIGRP but is getting the 150 150 0 0 16 routes from the RIP domain from Router A Because RIP has a lower administrative distance 120 than external EIGRP routes 170 Router B installs RIP routes for 150 150 0 0 16 only from Router A Example 7 37 shows the EIGRP topology table for Router B Example 7 37 Router B s EIGRP Topology Table for 150 150 0 0 16 Router B show ip eigrp topology 150 150 0 0 255 255 0 0 IP EIGRP topology entry for 150 150 0 0 16 State is Passive Query origin flag is 1 Successor s FD is 4294967295 Routing Descriptor Blocks 192 168 1 2 Serial0 from 192 168 1 2 Send flag is 0x0 Composite metric is 2707456 2195456 Route is External Vector metric Minimum bandwidth i
5. in which the query travels from the original router to the edge of the network and back to the original router 242 Chapter 7 Troubleshooting EIGRP Determining Active Stuck in Active Routes with show ip eigrp topology active Example 7 9 You must answer two questions to troubleshoot the EIGRP stuck in active problem Why is the route active Why is the route stuck Determining why the route is active is not a difficult task Sometimes the route that constantly is going active could be due to flapping link Or if the route is a host route 32 route it s possible that it is from a dial in connection that gets disconnected However trying to deter mine why the active route becomes stuck is a much harder task and more important to learn Usually an active route gets stuck for one of the following reasons Bad or congested links Low router resources such as low memory or high CPU on the router Long query range Excessive redundancy By default the stuck in active timer is only three minutes In other words if the EIGRP neighbor doesn t hear a reply for the query in three minutes neighbors are reset This adds difficulty in troubleshooting EIGRP stuck in active because every time an active route is stuck you have only three minutes to track down the active route query path and hopefully find the cause The tool that you need to troubleshoot the EIGRP stuck in active error is the show ip eigrp topology act
6. 1 Total delay is 102000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 8 Router A show ip eigrp topology 150 150 0 0 255 255 0 0 IP EIGRP topology entry for 150 150 0 0 16 State is Passive Query origin flag is 1 1 Successor s FD is 4269056 Routing Descriptor Blocks 10 1 1 2 Serial from 10 1 1 2 Send flag is 0x0 Composite metric is 4269056 3757056 Route is External Vector metric Minimum bandwidth is 1544 Kbit Total delay is 102000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 8 External data Originating router is 192 168 9 1 AS number of routes is 0 External protocol is OSPF external metric is 64 Administrator tag is 0 Troubleshooting EIGRP Route Flapping This section discusses how to troubleshoot consistent EIGRP route flapping The most important tool for troubleshooting this problem is the show ip eigrp event command This command reveals which neighbor is updating and the metric with which it s updating See Figure 7 27 for the flowchart for troubleshooting the EIGRP route flapping problem When troubleshooting EIGRP route flap problems a difference exists between the route disappearing from the routing table and the route timer in the routing table showing 00 00 00 as highlighted in Example 7 46 272 Chapter 7 Troubleshooting EIGRP Figure 7 27 Flowchart for Troubleshooting EIGRP Route
7. 1 24 172 16 4 1 24 _ Z Example 7 19 shows the configurations for Routers A B and C in the hub and spoke network in Figure 7 20 Example 7 19 Configurations for Routers A B and C in Figure 7 20 Router A interface ethernet 0 ip address 172 16 1 1 255 255 255 0 interface serial 0 ip address 172 16 2 1 255 255 255 0 router eigrp 1 network 172 16 0 0 Router B interface ethernet 0 ip address 172 16 3 1 255 255 255 0 interface serial 0 ip address 172 16 2 2 255 255 255 0 router eigrp 1 network 172 16 0 0 Router C interface ethernet 0 ip address 172 16 4 1 255 255 255 0 interface serial 0 ip address 172 16 2 3 255 255 255 0 router eigrp 1 network 172 16 0 0 A common network environment shown in Figure 7 20 is the Frame Relay hub and spoke design in which the hub router Router A in Figure 7 20 doesn t have a subinterface configured Troubleshooting EIGRP Route Advertisement 255 for each remote spoke site As a result the hub router uses a main interface to connect to the two spoke sites The problem is that Router B doesn t receive the routes for Router C s Ethernet network of 172 16 4 0 24 and Router C doesn t receive the routes for Router B s Ethernet net work of 172 16 3 0 24 The problem seems to be at the hub site The hub site sees all the routes but the hub site is not passing the routes from Router B to Router C and vice versa Example 7 20 shows the debug output on
8. 2 1 0 24 that just went away Router A doesn t have a feasible successor to go to as a backup route Router A has no choice but to put the 20 2 1 0 24 route into active state and query its neighbor Router B Notice the output of show ip eigrp topology active in Router A The 20 2 1 0 24 route has gone active for 1 minute and 12 seconds and the neighbor that has not responded is listed as 10 1 1 2 from Serial0 which is Router B The next step is to Telnet to Router B to see the active route status in Router B Figure 7 13 shows the active route status in Router B by performing the command show ip eigrp topology active In Figure 7 13 the command show ip eigrp topology active on Router B shows that the route 20 2 1 0 24 is also in active status in Router B and that it has gone active for 1 minute and 23 seconds Most importantly Router B can t reply to Router A about route 20 2 1 0 24 because Router B is still waiting for the neighbor with IP address of 10 1 3 2 Router D from Serial1 2 to reply to the query The next step is to go to Router D to see the status of the active route 20 2 1 0 24 and see why Router D has not replied to the query Figure 7 14 shows the output of show ip eigrp topology active on Router D Router D also put the route 20 2 1 0 24 in active state and it has been in active state for 1 minute and 43 seconds Router D can t answer Router B s query because Router D is waiting for the router with the IP address of 10 1 5 2
9. 255 255 255 0 router eigrp 1 network 172 16 0 0 Router C interface ethernet 0 ip address 172 16 4 1 255 255 255 0 interface serial 0 ip address 172 16 5 2 255 255 255 0 router eigrp 1 network 172 16 0 0 When subinterfaces are configured in Router A this logically separates the connection to Router B and Router C Each connection to Router B and Router C has its own network For example the connection from Router A to Router B is now through connection Serial 0 1 over the 172 16 2 0 24 network and the connection from Router A to Router C is now through connection Serial 0 2 over the 172 16 5 0 24 network Because Router A has two logical connection to Routers B and C over two different logical interfaces the split horizon rule doesn t apply and Router A will advertise all the routes to routers B and C as shown in Example 7 24 Verifying That Configuring the Subinterface with Different Subnets Solves the Split Horizon Problem Router A debug ip eigrp IP EIGRP 172 16 1 0 24 IP EIGRP 172 16 4 0 24 do advertise out Seriald do advertise out Seriald IP EIGRP 172 16 5 0 24 do advertise out Serial0 IP EIGRP 172 16 1 0 24 do advertise out Serial0 IP EIGRP 172 16 2 0 24 do advertise out Serial0 IP EIGRP 172 16 3 0 24 do advertise out SerialQ DO INS a With Router A advertising all the routes to the remote Routers Routers B and C now can reach each other s LAN interface Troubleshooting E
10. E s serial interface to see what happens Example 7 13 shows the result of the ping test Example 7 13 Result of ping Test from Router D to Router E Router D ping 10 1 5 2 Type escape sequence to abort Sending 5 100 byte ICMP Echos to 10 1 5 2 timeout is 2 seconds Success rate is percent 0 5 The ping test in Example 7 13 shows the success rate is 0 percent This test shows that a link problem exists between Router D and Router E The link is capable of passing a multicast packet to establish an EIGRP neighbor relationship but it is having problems transmitting a unicast packet This link problem is the root cause of the EIGRP stuck in active problem in this example The way to troubleshoot the EIGRP stuck in active problem is to chase hop by hop the query path and find out the status of active route at each hop The aforementioned process is typical troubleshooting methodology for combatting the EIGRP stuck in active problem Sometimes chasing the query path hop by hop leads to a loop or there are simply too many neighbors that didn t reply to the query In this case simplify and reduce the complexity of the EIGRP topology by cutting down the redundancy The simpler the EIGRP topology is the simpler it is to troubleshoot an EIGRP stuck in active problem The ultimate solution for preventing the EIGRP stuck in active problem is to manually sum marize the routes whenever possible and to have a hierarchical network
11. RTR B will reset the neighbor relationship with the log indicating RETRY LIMIT EXCEEDED and the process starts again Also keep in mind that the 16 times retransmission of the same packet is done using unicast not multicast Therefore the RETRY LIMIT EXCEEDED message indicates a problem with transmitting unicast packets over the link and this is most likely a Layer 1 or Layer 2 problem The solution to this problem is to troubleshoot from a Layer 2 perspective In this example a call to the WAN provider is needed to find out why the circuit from RTR B to RTR A is broken After the link between RTR B to RTR A is fixed the problem will be resolved Output from show ip eigrp neighbors in Example 7 2 shows that the neighbor relationship after the WAN link has been fixed show ip eigrp neighbors Command Output Confirms Problem Resolution RtrB show ip eigrp neighbors IP EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq sec ms Cnt Num 1 10 88 18 2 SO 14 01 26 30 149 894 0 291 Notice that the Q count column is 0 and that the SRTT and RTO have valid values now Troubleshooting EIGRP Neighbor Relationships 233 EIGRP Neighbor Problem Cause Uncommon Subnet Many times EIGRP won t establish neighbor relationships because the neighbors are not in the same subnet Usually the cause of this problem is router misconfiguration When EIGRP has problems establishing neighbor relationships because of an un
12. change route filter 228 Chapter 7 Troubleshooting EIGRP Figure 7 1 illustrates a general troubleshooting flowchart on EIGRP neighbor relationships Figure 7 1 General Flowchart on Troubleshooting EIGRP Neighbor Relationships EIGRP neighbor relationship problem Possible causes Layer 2 problem Unidirectional link Access list No Uncommon subnet K value mismatch AS number mismatch Refer to the appropriate Yes book section for further explanation Perform show ip eigrp neighbor Is the neighbor up Is the neighbor resetting No gt Go to other side of neighbor Repeat first step Yes Look at the log Note the reason for the neighbor reset Refer to book section for explanation of the reason Consulting the EIGRP Log for Neighbor Changes Whenever EIGRP resets its neighbor relationship it is noted in the log with the reason for the reset In the earlier Cisco IOS Software releases configuration to enable this feature is required The command eigrp log neighbor change is configured under router EIGRP In Cisco IOS Software Release 12 1 3 and later the eigrp log neighbor change command becomes the default setting for the router An example of the EIGRP neighbor log looks something like this DUAL 5 NBRCHANGE IP EIGRP EIGRP AS number Neighbor neighbor IP address is down reason for neighbor down Table 7 1 documents the nei
13. design The more network EIGRP summarizes the less work EIGRP has to do when a major convergence takes Troubleshooting EIGRP Neighbor Relationships 249 place Therefore this reduces the number of queries being sent out and ultimately reduces the occurrence of an EIGRP stuck in active error Figure 7 16 shows an example of a poor network design that will not scale in a large EIGRP network Figure 7 16 Example of a Nonscalable EIGRP Network 1 1 4 0 m 2 2 1 0 x core aj aoe 3 3 4 0 T r aaa _ gt Core lt 2 Core 19 1 4 0 A Cori 3 3 4 0 ea 1 1 2 0 1 1 3 0 Ec aw er lt 5 Zi 2 2 3 0 2 2 2 0 Ol T ane es e 3 3 4 0 t en T2 2 2 1 0 RO 3 3 4 0 es E 3 3 3 0 y t D 2 2 2 0 1 1 2 0 2 2 3 0 In Figure 7 16 each core router represents a region of the entire network and shows that there is no hierarchy in IP addressing scheme The Core 1 router is injecting routes 1 1 1 0 3 3 4 0 1 1 2 0 and 2 2 3 0 into the core network The addresses are so scattered that no manual summarization is possible The other core routers are experiencing the same problem The Core 3 and Core 4 routers can t summarize any routes into the core network As a result if the Ethernet link of the 3 3 3 0 network keeps flapping the query would travel to the Core 3 router and then the query also would be seen in the Core 1 and Core 4 region Ultimately the query will traverse to all the routers in the internetwork this would dra
14. for Router B s Ethernet 0 interface Properly Configuring the Subnet Mask for Router B s Ethernet 0 Interface Router B interface ethernet 0 ip address 172 16 4 1 255 255 255 128 This change now causes Router B to send an EIGRP update of 172 16 4 0 25 to Router A which causes Router A to use the EIGRP route instead of the floating static route Example 7 72 shows what Router A s routing table now looks like Routing Table for 172 16 4 0 on Router A After the Configuration Change in Example 7 71 Router A show ip route 172 16 4 0 Routing entry for 172 16 4 0 25 Known via EIGRP 1 distance 90 metric 2195456 type internal Redistributing via eigrp 1 Last update from 172 16 2 2 on Serial 00 10 30 ago Routing Descriptor Blocks 172 16 2 2 from 172 16 2 2 00 10 30 ago via Serial 0 Route metric is 2195456 traffic share count is 1 Total delay is 21000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 The traffic stops flowing to the BRI 0 interface and starts to flow to the primary link The BRI interface then goes down and moves to backup mode again EIGRP Error Messages 291 EIGRP Error Messages Some EIGRP error messages that occur in the log have mystified many network admin istrators This section discusses some of the most common EIGRP errors that appear and the meanings behind these EIGRP error messages DUAL 3 SIA This me
15. getting redistributed into the EIGRP domain 282 Chapter 7 Troubleshooting EIGRP Referring to Figure 7 33 you can see that the 150 150 0 0 16 network is present in the RIP domain and the OSPF domain Before the route is getting redistributed into EIGRP the route must be in the EIGRP topology table first Look at the EIGRP topology table on Router A for the 150 150 0 0 16 network in Example 7 58 Example 7 58 EIGRP Topology Table for 150 150 0 0 16 Router A show ip eigrp topology 150 150 0 0 255 255 0 0 Route not in topology table As this output shows the route 150 150 0 0 16 is not even in the EIGRP topology table Example 7 59 shows the routing table for the 150 150 0 0 16 network Example 7 59 Routing Table for 150 150 0 0 16 Example 7 60 Router A show ip route 150 150 0 0 255 255 0 0 Routing entry for 150 150 0 0 16 Known via OSPF 1 distance 110 metric 186 Redistributing via OSPF 1 Last update from 172 16 2 2 on Ethernet 1 Routing Descriptor Blocks 172 16 2 2 from 172 16 2 2 00 10 23 ago via Ethernet 1 Route metric is 186 traffic share count is 1 The output in Example 7 59 shows that the 150 150 0 0 16 route is showing up as an OSPF route not a RIP route This is why the route is not getting redistributed into EIGRP Before RIP routes are redistributed into EIGRP the router looks at the routing table and redistributes all the RIP routes into EIGRP As Example 7 59 shows the router hears t
16. in Example 7 50 shows that Router A is constantly getting updates from 10 1 1 3 Router D for the route 150 150 0 0 16 Notice that the next hop router that updates Router A does not reset the route timer in Router A Any feasible successor that updates a router about a route resets the route timer on the router Therefore the route timers are reset but the route stays in the routing table so that the router won t drop any packets From the EIGRP event log it s Router D that constantly sends updates to Router A The next step is to go to Router D to investigate why it is updating Router A with updates One possible reason that this update is constantly occurring is that there is a routing loop in Router D for 150 150 0 0 16 route with other routers in network X causing the routes to be sent to each other If a routing loop occurs in the network you need a current network diagram to go hop by hop to each router to track the routing loop Another possibility might be that the LAN switch on Router A s Ethernet 0 might have a spanning tree problem that keeps looping the packets from Router D to Router A If no routing loop is in the network and no spanning tree problem is on the switch the other possibility is that Router D might be running into an EIGRP bug in which it is constantly sending out updates to Router A for no reason One of the possible bugs might be CSCdt15109 in which the router constantly sends out updates that is not changing
17. router simply refreshes the timer because it got an update from one of the neighbors To truly verify that the router is taking out the route from the routing table and reinstalling it use the debug ip routing Example 7 47 demonstrates the output from this command on Router B Troubleshooting EIGRP Route Flapping 273 Example 7 47 debug ip routing Command Output Verifies Whether a Route Is Being Installed Router B debug ip routing RT add 150 150 0 0 16 via 10 1 1 2 eigrp metric 90 304128 RT delete route to 150 150 0 0 via 10 1 1 2 eigrp metric 90 304128 This debug shows all the routes that the routing table takes out and installs although the output of the debug might be overwhelming to the routers You can also use an access list to the debug so that the output shows only the routes in question For example if you want to do the debug only on the route 192 168 1 0 24 in the routing table use an access list as configured in Example 7 48 Example 7 48 Using Access Lists to Limit debug ip routing Information Router B debug ip routing 1 access list 1 permit 192 168 1 0 0 0 0 255 access list 1 deny any As previously mentioned your best tool in troubleshooting EIGRP route flap is the show ip eigrp event command By default the router keeps a log of all EIGRP events However the log size is only 500 lines which covers only a few hundred milliseconds of EIGRP events The show ip eigrp event command
18. routing loop or repeat test on downstream router Break routing loop by reducing number of EIGRP neighbors Lots of lt No redundancy Yes No y Reduce redundancy by reducing the number of EIGRP Ping interface to neighbor that doesn t respond with large and small packet Ping success neighbors Yes Problem with link between routers Check for Layer 1 or Layer 2 link problems Fixing link problem will fix EIGRP SIA problem Not interface problem Check router with CPU utlization and memory usage If router doesn t appear to have memory or CPU problems reduce EIGRP network redundancy by reducing the number of EIGRP neighbors Consider the network shown in Figure 7 12 for an example of troubleshooting the EIGRP stuck in active problem Troubleshooting EIGRP Neighbor Relationships 245 Figure 7 12 Network Topology for EIGRP Stuck in Active Troubleshooting Example 20 2 1 0 24 Sim 1 10 12 0124 F zee lt ee D t p 10 1 1 0 24 Ca 1 10 1 3 0 24 10 1 4 0 24 2 AE Router A show ip eigrp topology active T IP EIGRP Topology Table for AS 1 ID 20 2 1 1 D A 20 2 1 0 24 1 successors FD is Inaccessible 1 replies active 00 01 12 query origin Local origin via Connected Infinity Infinity Ethernet 10 1 5 0 24 Remaining replies via 10 1 1 2 r Serial In Figure 7 12 Router A has an Ethernet interface with network 20
19. so eo ts y 172 16 1 1 24 US 10 0 0 0 8 172 16 3 1 24 Example 7 63 Example 7 64 172 16 1 2 24 Network coming from Network Cloud Y From the setup shown in Figure 7 34 Router B is redistributing from OSPF to EIGRP The 10 0 0 0 8 network comes from the OSPF domain and is being redistributed into EIGRP domain by Router B However Router A never sees the 10 0 0 0 8 route in its routing table Example 7 63 shows the configuration of Router A and Router B and Example 7 64 shows the routing table of 10 0 0 0 8 route in Router A and Router B Configurations for Routers A and B for Network Setup in Figure 7 34 Router A interface ethernet 0 ip address 172 16 3 1 255 255 255 0 interface serial 0 ip address 172 16 1 1 255 255 255 0 router eigrp 1 network 172 16 0 0 Router B interface ethernet 0 ip address 172 16 2 1 255 255 255 0 interface serial 0 ip address 172 16 1 2 255 255 255 0 router ospf 1 network 172 16 0 0 0 0 255 255 area 0 router eigrp 1 network 172 16 0 0 redistribute ospf 1 Routing Table and EIGRP Topology Table for 10 0 0 0 8 Route in Routers A and B Router_A show ip route 10 0 0 0 255 0 0 0 Network not in table Router_A show ip eigrp topology 10 0 0 0 255 0 0 0 Route not in topology table Troubleshooting EIGRP Redistribution Problems 285 Example 7 64 Example 7 65 Routing Table and EIGRP Topology Table for 10 0 0 0 8 Route in Routers A and B Continued Router_
20. that the neighbor 10 1 5 2 from interface Serial1 2 has not replied to the query To proceed further with troubleshooting you must Telnet to the 10 1 5 2 router to see the status of its EIGRP active routes using the same command show ip eigrp topology active Sometimes the router does not list the neighbors that have not replied to the queries under the Remaining replies section Example 7 10 shows another output of show ip eigrp topology active Example 7 10 Another Sample Output of the show ip eigrp topology active Command Example 7 11 Router show ip eigrp topology active IP EIGRP Topology Table for AS 110 1D 175 62 8 1 A 11 11 11 0 24 1 successors FD is Inaccessible 1 replies active 00 02 06 query origin Successor Origin via 1 1 1 2 Infinity Infinity r Seriali1 0 serno 171 via 10 1 1 2 Infinity Infinity Serial1 1 serno 173 In Example 7 10 the only difference in output from Example 7 9 is the list of neighbors that have not replied to the router However this doesn t mean that all of the neighbors have replied to the queries In Example 7 10 neighbor 1 1 1 2 has an r next to the address of 1 1 1 2 This also means that the neighbor has not replied to the queries In other words the router has two ways of representing neighbors that have not replied to the queries One is to have them listed under the Remaining replies section the other is to have an r next to the neighbor interface IP address When using the sh
21. this problem and how to resolve them For overall troubleshooting methods Figure 7 24 shows the flowchart for troubleshooting EIGRP route installation problems Figure 7 24 Flowchart for Troubleshooting EIGRP Route Installation Problems EIGRP is not installing routes into the routing table Is EIGRP neighbor relationship established Check EIGRP topology table Are routes in topology table Neighbor problem See section on troubleshooting EIGRP neighbor relationship Yes Is EIGRP neighbor flapping after few minutes Are routes in topology table with Yes FD metric inaccessible No Call TAC for further Yes assistance Link problem ing interface with large 1400 byte No Troubleshoot Layer 2 Routes from other routing nd small 100 byte packets problem protocol with better administrative Ping successful distance or summary route are configured Check for duplicate router ID issue might have same IP address as other routers in the network Check distribute list Is it misconfigured No gt Correct the distribute list configuration Troubleshooting EIGRP Route Installation 265 EIGRP Is Not Installing Routes Cause Auto or Manual Summarization When EIGRP fails to install routes in the routing table the first thing to check is the topology table Figure 7 25 shows th
22. 0 router eigrp 1 network 172 16 0 0 offset list 1 out 600000 serial 1 access list 1 permit 172 16 0 0 0 0 255 255 The problem is that Router A is not taking the direct paths to Router C to reach Router C s Ethernet network of 172 16 5 0 24 Instead Router A takes the path to Router B and then to Router C This takes an extra hop Example 7 30 shows the routing table and the EIGRP topology table for 172 16 5 0 255 255 255 0 for Router A show ip route and show ip eigrp topology Command Output Reveals the Routes That Router A Is Taking to Reach Router C s 172 16 5 0 24 Ethernet Network Router_A show ip route 172 16 5 0 Routing entry for 172 16 5 0 24 Known via eigrp 1 distance 90 metric 2707456 type internal Redistributing via eigrp 1 Last update from 172 16 2 2 on Serial 01 08 13 ago Routing Descriptor Blocks 172 16 2 2 from 172 16 2 2 01 08 13 ago via Serialo Route metric is 2707456 traffic share count is 1 Total delay is 41000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 2 Router A show ip eigrp topology 172 16 5 0 255 255 255 0IP EIGRP topology continues 262 Chapter 7 Troubleshooting EIGRP Example 7 30 Example 7 31 show ip route and show ip eigrp topology Command Output Reveals the Routes That Router A Is Taking to Reach Router C s 172 16 5 0 24 Ethernet Network Continued entry for 172 16 5 0 24 State is Passive Q
23. 130 2 ip route 192 168 4 0 255 255 255 0 192 168 130 2 ip route 192 168 127 0 255 255 255 0 192 168 130 2 EIGRP Is Advertising Routes with Unexpected Metric Not only might EIGRP advertise unexpected routes to its neighbors but it also might advertise an unexpected metric to its neighbors The EIGRP metric is the basis of route selection done by EIGRP which selects the route with the lowest EIGRP metric to the destination network An unexpected EIGRP metric being sent or received on the router 260 Chapter 7 Troubleshooting EIGRP might alter route selection to the destination network The end result might be suboptimal routing Figure 7 22 shows the flowchart for troubleshooting such an issue Figure 7 22 Flowchart for Troubleshooting EIGRP Advertisement of Routes with Unexpected Metric Value EIGRP advertises routes with unexpected metric Metric advertised uses total interface delay across path Call TAC for further Is the offset list configured assistance Yes Yes Metric advertised uses lowest bandwidth across path Offset list changes the delay portion of EIGRP metric Yes Other issues might be involved Check for K values K values can be changed to cause strange metric value The case study that follows is a case of an offset list that is created inadvertently causing the router to route packets in a suboptimal fashi
24. 255 0 interface serial 0 ip address 172 16 2 2 255 255 255 0 interface bri 0 ip address 172 16 3 2 255 255 255 0 encapsulation PPP dialer map IP 172 16 3 1 name Router A broadcast xxx ppp authentication chap dialer group 1 router eigrp 1 network 172 16 0 0 continues 290 Chapter 7 Troubleshooting EIGRP Example 7 70 Router B Configuration After Reload Continued Example 7 71 Example 7 72 access list 101 deny eigrp any any access list 101 permit IP any any dialer list 1 protocol IP list 101 ip route 172 16 1 255 255 255 128 172 16 3 1 200 Notice that now in Ethernet 0 s configuration in Router B the IP address is 172 16 4 1 255 255 255 0 the mask has changed from 25 to 24 This is the cause of the problem When Router B advertises its Ethernet 0 route to Router A it advertises the 172 16 4 0 24 route to Router A and Router A still installs the floating static route of 172 16 4 0 25 The routing table shows the 25 route because it has a longer subnet mask The wrong mask appears because when the network administrator reloaded Router B Router B used the old configuration that it had stored and Ethernet 0 s old subnet mask a 24 before the network administrator changed it to 25 When the change is made the network administrator didn t save the configuration The solution to this problem is to change the IP address subnet mask in Router B to the 25 subnet mask Example 7 71 shows the configuration
25. 7 22 shows the debug output on Router A after the configuration change Verifying That Disabling Split Horizon Corrected the Problem Router A debug ip eigrp IP EIGRP 172 16 1 0 24 do advertise out Serial IP EIGRP 172 16 3 0 24 do advertise out Seriald IP EIGRP 172 16 4 0 24 do advertise out Seriald IP EIGRP Processing incoming UPDATE packet IP EIGRP Int 172 16 3 0 24 IP EIGRP Int 172 16 4 0 24 Now the spoke Routers B and C can see the routes Another fix for the split horizon problem is to configure subinterfaces on the hub router and assign different IP address subnets for each subinterface Keep in mind that the support of a serial subinterface is 256 Chapter 7 Troubleshooting EIGRP Example 7 23 Example 7 24 valid for only the WAN PVC type of connection such as ATM or Frame Relay Example 7 23 shows the configuration for such a setup to avoid the EIGRP split horizon problem Configuring Subinterfaces with Different IP Address Subnets to Combat EIGRP Split Horizon Problems Router A interface ethernet 0 ip address 172 16 1 1 255 255 255 0 interface serial 0 1 point to point description connection to router B ip address 172 16 2 1 255 255 255 0 interface serial 0 2 point to point description connection to router C ip address 172 16 5 1 255 255 255 0 router eigrp 1 network 172 16 0 0 Router B interface ethernet 0 ip address 172 16 3 1 255 255 255 0 interface serial 0 ip address 172 16 2 2
26. B show ip route 10 0 0 0 255 0 0 0 Routing entry for 10 0 0 0 8 Known via OSPF 1 distance 110 metric 206 Redistributing via OSPF 1 Last update from 172 16 2 2 on Ethernet 0 Routing Descriptor Blocks 172 16 2 2 from 172 16 2 2 00 18 13 ago via Ethernet 0 Route metric is 206 traffic share count is 1 Router_B show ip eigrp topology 10 0 0 0 255 0 0 0 Route not in topology table From the output of Example 7 64 notice that Router B has the 10 0 0 0 24 route in its routing table as an OSPF route but Router A doesn t have the routing entry for 10 0 0 0 8 Also the EIGRP topology table on Router B doesn t even have the entry for the 10 0 0 0 8 route You can conclude from this that the OSPF to EIGRP redistribution in Router B is not working By looking over the configuration in Router B you notice that although the redistribute ospf 1 command is configured under EIGRP there is no configuration of the default metric command When redistributing between different routing protocols the default metric com mand must be configured When one routing protocol is being redistributed into another the router doesn t have a way to translate the routing metric from one routing protocol into another The default metric command is used so that the network administrator can manually initialize the routing metric during route redistribution The fix for this problem Configure a default metric under EIGRP in Router B Example 7 65 shows th
27. Cisco IOS Software Release 12 1 7 and later will have the bug fix for this issue however it is always recommended to consult with Cisco TAC to determine whether the problem is caused by a software bug In this example Router D is running into the software bug previously mentioned Notice that the problem is not on Router A but on Router D Router D constantly sends out updates to Router A and Router A constantly refreshes its timer Router A is simply a result of the problem caused by Router D After a Cisco IOS Software upgrade on Router D Router A stops refreshing its routing table timer as indicated in Example 7 51 Also performing the show ip eigrp event several times in succession shows that the timers on the event table are not changing This also verifies that the EIGRP process is stable and is not receiving unnecessary updates from its neighbors Output of Routing Table on Router A to Verify the Fix of the Problem Router_A show ip route 150 150 0 0 Routing entry for 150 150 0 0 16 Known via eigrp 1 distance 90 metric 4269056 type internal Redistributing via eigrp 1 Last update from 10 1 1 2 on ethernet 00 03 18 ago Routing Descriptor Blocks 10 1 1 2 from 10 1 1 2 00 03 18 ago v ia ethernetO Route metric is 4269056 traffic share count is 1 Total delay is 102000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 4 276 Chapter 7 Troubleshootin
28. Flapping EIGRP routes flap EIGRP neighbor problem Bo Yes See the section on Do shoW Ip eigrp event See troubleshooting EIGRP which neighbor is updating with infinity metric and investigate neighbor relationship from that neighbor Check EIGRP neighbor status Is the neighbor flapping Ye No es Go to the router that originates the flapping route Is the interface Is route timer for the route in the routing table constantly showing Do debug ip routing Did the flapping route disappear from routing table Yes Interface problem Could be Do show ip eigrp event See bad interface Troubleshoot which neighbor s is constantly Layer 2 problem updating and investigate the neighbor No Example 7 46 Example of Routing Table That Shows the Update Timer Always at 00 00 00 Router A show ip route 150 150 0 0 Routing entry for 150 150 0 0 16 Known via eigrp 1 distance 90 metric 304128 type internal Last update from 10 1 1 2 on Ethernet 0 00 00 00 ago When the route timer in the routing table always shows 00 00 00 it doesn t necessarily mean that the router is constantly taking the route out and reinstalling it It simply means that one of the router s neighbors is constantly updating the router with the route The neighbor updating the route is not necessarily the best path to the route but it is one possible path The
29. GRP Neighbor Relationships 247 Figure 7 15 Active Route Status on Router E for the Troubleshooting EIGRP Stuck in Active Example 20 2 1 0 24 10 1 2 0 24 et 2 i nn 10 1 1 0 24 BIA 1 4 10 1 3 0 24 10 1 4 0 24 2 2 Ui 1 Router E show ip eigrp topology active IP EIGRP Topology Table for AS 1 ID 10 1 5 2 10 1 5 0 24 2 7 E j The output for show ip eigrp topology active didn t show anything for Router E This indicates that as far as Router E is concerned there are no routes in active state Now you should Telnet back to Router D to double check whether the router is still in the active state for route 20 2 1 0 24 Telnetting back to Router D shows that Router D is still in active state for route 20 2 1 0 24 but Router E doesn t have any routes in active state What s going on To summarize what has been going on so far the chain of event is as follows 1 Router A went active for route 20 2 1 0 24 and is waiting for Router B to reply to the query 2 Router B can t reply because it is waiting for Router D s query response 3 Router D can t reply because it is waiting for Router E to reply to the query 4 Finally the show ip eigrp topology active command in Router E shows that Router E does not think that any routes are active while going back to Router D shows that the route 20 2 1 0 24 is still in active state From this sequence of events you can see that there is clearly a discrepancy be
30. IGRP Route Advertisement 257 EIGRP Is Advertising Routes to Neighbors When the Network Administrators Think That It Shouldn t Sometimes EIGRP advertises unexpected routes to its neighbors See Figure 7 21 for a flowchart of troubleshooting EIGRP unexpected advertisement of routes Figure 7 21 Flowchart for Troubleshooting EIGRP Unexpected Advertisement of Routes EIGRP advertises routes unexpectedly Static route configured with next hop being an interface heck Distribute List Misconfigured distribute list command Check Manual Summarization No configuration Misconfigured summarization command Yes Possible bug Call TAC for further assistance Yes Correct the configuration of EIGRP manual summarization Yes Is next hop interface covered under EIGRP network statement Distribute List issue Correct the configuration of distribute list Yes Normal behavior Static routes will be advertised via EIGRP automatically if static routes have next hop as interface that is covered under EIGRP network statement Refer to Figure 7 19 for the network diagram on this example Example 7 25 shows the configurations for Routers A and B Example 7 25 Configuration of Router A and Router B for the Example Shown in Figure 7 19 Router A interface ethernet 0 ip address 172 16 3 1 255 255 255 0 interface serial 0 ip address 10 1 1 1 255 255 255 0 router eigrp 1 netw
31. Router B for any nonexistent network in the 172 16 0 0 16 range This problem is more of a design issue The main issue is that Router B s summary route is too broad and includes nonexistent subnets Also Router A is sending a more general summary route default route to Router B The solution is to have Router B send out only the summary route that covers the 172 16 1 0 through 172 16 15 0 networks In other 280 Chapter 7 Troubleshooting EIGRP words instead of sending the 172 16 0 0 16 summary route Router B can send the 172 16 0 0 255 255 240 0 summary route to Router A Therefore when Router A tries to look at the routing table for the 172 16 40 0 24 entry the routing table simply returns with Network not in table message and drops the packet instead of sending it to Router B which ends the loop problem Troubleshooting EIGRP Redistribution Problems In many instances a problem occurs when redistributing from another routing protocol into EIGRP Figure 7 32 shows a flowchart for troubleshooting EIGRP redistribution Flowchart for Troubleshooting EIGRP Redistribution Problem Router doesn t redistribute another protocol s routes into EIGRP Is default metric command configured under router EIGRP Yes Do routes appear in the routing table as from other routing protocol Yes If routes are not advertised to the neighbor See the section on Troubleshooting EIGRP Rout
32. This chapter covers the following EIGRP troubleshooting topics Troubleshooting EIGRP neighbor relationships Troubleshooting EIGRP route advertisement Troubleshooting EIGRP route installation Troubleshooting EIGRP route flap Troubleshooting EIGRP route summarization Troubleshooting EIGRP route redistribution Troubleshooting EIGRP dial backup EIGRP error messages CHAPTER Troubleshooting EIGRP This chapter discusses some of the common problems in EIGRP and how to resolve those problems Debugs configurations and useful show commands are also given where necessary NOTE Debugs can be CPU intensive and can adversely affect your network Therefore debugs are not recommended on a production network unless being instructed by Cisco s Technical Assistance Center TAC Sometimes there might be multiple causes for the same problem Therefore if one scenario doesn t fix the network problem always check into other scenarios Troubleshooting EIGRP Neighbor Relationships This section discusses methods of troubleshooting issues regarding EIGRP neighbor relationships The following are the most common causes of problems with EIGRP neighbor relationships Unidirectional link Uncommon subnet primary and secondary address mismatch Mismatched masks K value mismatches Mismatched AS numbers Stuck in active Layer 2 problem Access list denying multicast packets Manual change summary router metric
33. affic share count is 1 Total delay is 21000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 EIGRP Is Not Installing Routes Cause Duplicate Router IDs Many times EIGRP will not install routes because of a duplicate router ID problem EIGRP does not use router ID as extensively as OSPF EIGRP uses the notion of router ID only on external routes to prevent loops EIGRP chooses the router ID based on the highest IP address of the loopback interfaces on the router If the router doesn t have any loopback interfaces the highest active IP address of all the interfaces is chosen as the router ID for EIGRP Figure 7 26 shows the network setup for such a case study on EIGRP router IDs Troubleshooting EIGRP Route Installation 269 Figure 7 26 EIGRP Network Susceptible to EIGRP Not Installing Routes Because of Duplicate Router IDs Network Cloud Y ea ieee 192 168 1 1 32 E so 2205 U E Us wy EO 10 1 2 1 24 10 1 2 3 24 192 168 1 1 24 Example 7 41 shows the pertinent configurations for the cause of this problem Example 7 41 Configurations for Routers A B C and X in Figure 7 26 Router A interface ethernet 0 ip address 192 168 1 1 255 255 255 0 interface serial 0 ip address 10 1 1 1 255 255 255 0 Router B interface serial 0 IP address 10 1 1 2 255 255 255 0 interface serial 1 IP address 10 1 2 1 255 255 255 0 Router C interfac
34. atic distance 200 metric 0 Routing Descriptor Blocks 172 16 3 2 Route metric is traffic share count is 1 The output in Example 7 68 shows that Router A still is installing the floating static route to Router B s Ethernet network The next step is to make sure that EIGRP neighbors are properly established between Router A and Router B over the primary interface You can verify this with the show ip eigrp neighbor command as demonstrated on both Router A and Router B in Example 7 69 Example 7 69 Verifying an EIGRP Neighbor Relationship Between Routers A and B Router A show ip eigrp neighbor IP EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq sec ms Cnt Num 0 172 16 2 2 SO 12 00 10 23 21 200 1 23 1 172 16 3 2 BRIO 12 00 10 23 40 240 1 50 Router B show ip eigrp neighbor IP EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq sec ms Cnt Num 172 16 2 1 SO 12 00 10 30 21 200 0 24 1 172 16 3 1 BRIO 12 00 10 30 40 240 1 51 The neighbor relationship looks fine from both routers Both Routers A and B show that the neighbors are established without a problem The next step is to look at the configuration on Router B to make sure that everything is configured properly Example 7 70 shows Router B s configuration after reload Example 7 70 Router B Configuration After Reload Router B interface ethernet 0 ip address 172 16 4 1 255 255
35. common subnet the following error message appears IP EIGRP Neighbor ip address not on common subnet for interface Figure 7 5 shows the flowchart for troubleshooting the problem when the Neighbor not on common subnet error appears on the router Figure 7 5 Problem Resolution Flowchart Getting EIGRP error EIGRP neighbor not on common subnet Double check interface configuration Misconfigured IP address on interface on local and neighboring router Correct the IP address configuration on interface No s primary address of interface in the same subnet as the primary address of neighboring router No gt Change IP address of interface so the primary address of the neighboring router is in the same subnet as the local router Yes Connection between EIGRP neighbor done through a LAN hub Yes gt LAN hub will pass broadcast and multicast packets to other ports between logical segments Break up broadcast domain by using separate hub for each logical LAN segment or configure no EIGRP log neighbor warnings to stop seeing error message No If connection between EIGRP neighbor is made on switch make sure that the switch configuration is correct Make sure two different LAN segments are not configured to be in the same VLAN sharing the same broadcast domain 234 Chapter 7 Troubleshootin
36. e No sure that passive interface or access list is not configured High CPU utilization on router Check incorrect interface access list or Layer 1 Layer 2 problem Check switch between the link Check interface errors Check with WAN connection provider Bad Interface change hardware No gt ag Ping to address 224 0 0 10 from neighbor Response No Yes Repeat troubleshooting steps from neighbor router or Cause could be because of network congestion Increase the neighbor hold time and monitor EIGRP Neighbor Problem Cause Unidirectional Link Sometimes a problem with a WAN connection causes EIGRP to have a one way neighbor relationship A one way neighbor relationship usually is caused by a unidirectional connection between the neighbors The cause for unidirectional connection is usually a Layer 2 problem For example a link might be experiencing many CRC errors a switch problem or a ping test failure with large or small packets In this case you need a call to the group that is responsible for the link to check the integrity of the link Sometimes a simple misconfigured access list causes EIGRP to form a one way neighbor relationship Figure 7 4 illustrates an example of an EIGRP problem as a result of a unidirectional link Troubleshooting EIGRP Neighbor Relationships 231 Figure 7 3 Flowchart for Troubleshooting EIGRP Neighbor Relationship W
37. e Advertisement Configure default metric under router EIGRP Routes won t No gt redistribute into EIGRP without the default metric command Routes need to be in routing table as from other routing protocols before getting redistributed into EIGRP No Troubleshooting EIGRP Redistribution Problems 281 Consider the network diagram in Figure 7 33 in which the router is the border router between three routing protocols RIP OSPF and EIGRP Figure 7 33 Network Susceptible to EIGRP Redistribution Problems OSPF Domain EIGRP Domain EO 150 150 0 0 16 Network coming from Network Cloud Y 172 16 1 1 24 Example 7 57 shows Example 7 57 ip address 172 interface ethernet ip address 172 interface serial 0 ip address 172 router ospf 1 network 172 16 router rip network 172 16 172 16 3 1 24 RIP Domain 150 150 0 0 16 Network coming from Network Cloud X the configuration for Router A Configuration for Router A in Figure 7 33 Router A interface ethernet 0 16 1 1 255 255 255 0 ee 255 255 255 0 16 3 1 255 255 255 0 0 0 0 0 255 255 area 0 0 0 172 16 2 1 24 router eigrp 1 passive interface ethernet 1 network 172 16 0 0 redistribute rip default metric 10000 100 255 1 1500 Router A wants to redistribute all the routes in the RIP domain into the EIGRP domain The problem is that the network 150 150 0 0 16 is not
38. e corrected configuration of Router B Corrected Configurations of Router B to Fix the Redistribution Problem Shown in Figure 7 34 Router B interface ethernet 0 ip address 172 16 2 1 255 255 255 0 interface serial 0 ip address 172 16 1 2 255 255 255 0 router ospf 1 network 172 16 0 0 0 0 255 255 area 0 router eigrp 1 network 172 16 0 0 redistribute ospf 1 default metric 10000 100 255 1 1500 From Example 7 65 the default metric configured is default metric 10000 100 255 1 1500 10000 is the bandwidth in kilobits per second 100 is the interface delay in unit of 10 micro seconds 255 is interface reliability where 255 represents 100 percent reliable 1 is interface load where 255 represents 100 percent load The last number 1500 is the MTU of the inter face Because the 10 0 0 0 8 route comes from the Ethernet interface of Router B we are setting the default metrics that matches the Ethernet interface namely bandwidth of 10 000 kbps delay of 1000 ms 100 percent reliability 1 255 of interface load and an MTU of 1500 bytes Keep in mind that the router will accept any values for the default metric setting The router 286 Chapter 7 Troubleshooting EIGRP will even accept default metric value of 1 1 1 1 1 However using the default metric value that best matches the network topology will allow the router to make a better routing decision Now with the correct configuration in place in Router B Example 7 66 sho
39. e major network of 192 168 3 0 24 it does not install the network in the topology table because it already has the 192 168 3 0 network on its Ethernet interface Two solutions to the discontiguous network problem exist One is to configure the command no auto summary under router eigrp This command tells EIGRP not to autosummarize to major network boundaries As a result Router B s configuration will look like Example 7 18 Example 7 18 Disabling Autosummarization on Router B to Prevent Discontiguous Networks Router B router EIGRP 1 network 192 168 3 0 network 10 0 0 0 no auto summary The second solution is to change the IP address of the serial interfaces on each side of the link to the 192 168 3 0 subnet As an example the serial IP address can take 192 168 3 65 28 and 192 168 3 66 28 This way Router B won t autosummarize the route because it is not across a major network boundary EIGRP Is Not Advertising Routes to Neighbors Cause Split Horizon Issues EIGRP has its own split horizon command This command configured under the inter face is shown here no ip split horizon eigrp autonomous system 254 Chapter 7 Troubleshooting EIGRP Turning off IP split horizon does not turn off EIGRP split horizon Figure 7 20 shows an EIGRP network vulnerable to split horizon issues Figure 7 20 EIGRP Network Susceptible to EIGRP Split Horizon Problems 172 16 1 1 24 EO 172 16 2 2 24 S C3 i E0 A R E0 172 16 3
40. e network setup for this case study Figure 7 25 EIGRP Network Susceptible to Route Installation Problem Network Cloud 192 168 1 1 24 si Eza so gt 192 168 2 1 24 CS 176 16 2 1 24 p Ee om Network Cloud Y Example 7 33 shows the configuration for Router B Example 7 33 Configuration for Router B in Figure 7 25 Router B interface ethernet 0 ip address 172 16 2 1 255 255 255 0 interface serial 0 192 168 1 1 255 255 255 0 interface serial 1 192 168 2 1 255 255 255 0 router eigrp 1 network 172 16 0 0 network 192 168 1 0 network 192 168 2 0 Inside network clouds X and Y are networks in the 172 16 x x space The problem is that Router C summarizes all the 172 16 x x networks into one summary route of 172 16 0 0 16 and sends it to Router B Router B is not installing the routes in the routing table as shown in Example 7 34 Example 7 34 Router B s Routing Table Router B show ip route 172 16 0 0 Routing entry for 172 16 0 0 16 Routing Descriptor Blocks directly connected via Null 0 266 Chapter 7 Troubleshooting EIGRP Router B s routing table shows that the route is directly connected to Null 0 instead of learned from Router C The topology table in Router B shows that the router is getting the routes from Router C but is installing the route as connected because the Null 0 route has a distance of 5 which is an EIGRP summary route The configuration of Router B
41. e problem is happening When the stuck in active event is over and the network stabilizes it is extremely difficult if not impossible to backtrack the problem and find out the cause Figure 7 11 shows the flowchart for troubleshooting the EIGRP stuck in active problem Figure 7 11 Flowchart for Resolving the EIGRP Stuck in Active Problem EIGRP is getting stuck in active routes and resetting neighbors Usually caused by dial in PPP users or Continuously do show ip eigrp Are active routes Same route topology active Notice same Ku r ne we Or same set of fouter active host routes 32 or Yes flapping interfaces i gt 30 routes Summarizing routes will not responding to queries reduce SIA Same set of neighbor No TY not responding to qUerise Are active routes from one region of the network Telnet to a neighbor that has not responded to the query On show ip eigrp topology active Still waiting for other neighbor to reply Summarize routes No Check for summary routes Are proper summary routes in place Check for high CPU low memory or congested or bad link between routers Yes Check CPU utilization and make sure the router has ample memory Make sure the router has enough memory and low CPU utilization Fixing high CPU and memory problem will fix EIGRP SIA problem LN No Possible
42. e serial 0 ip address 10 1 2 2 255 255 255 0 Router X interface loopback 0 ip address 192 168 1 1 255 255 255 255 Router X is redistributing a route of 150 150 0 0 16 from OSPF into EIGRP and is sending the route several hops to Router C Router C receives the route and sends the route as EIGRP external routes to Router B Router B installs the route in the routing table and sends it to Router A The debug output in Example 7 42 verifies how Router B sends the route to Router A Example 7 42 debug ip eigrp Command Output on Router B Router B debug ip eigrp IP EIGRP 150 150 0 0 16 do advertise out serial 0 The problem is that Router A is not installing the 150 150 0 0 16 route in the routing table As a matter of fact Router A is not showing the 150 150 0 0 16 route in its topology table Going back to Router B the route is in the routing table and the topology table appears as shown in Example 7 43 270 Chapter 7 Troubleshooting EIGRP Example 7 43 EIGRP Topology Table for 150 150 0 0 16 on Router B Router B show ip eigrp topology 150 150 0 0 255 255 0 0 IP EIGRP topology entry for 150 150 0 0 16 State is Passive Query origin flag is 1 1 Successor s FD is 3757056 Routing Descriptor Blocks 10 1 2 2 Serial1 from 10 1 2 2 Send flag is 0x0 Composite metric is 3757056 3245056 Route is External Vector metric Minimum bandwidth is 1544 Kbit Total delay is 82000 microseconds Reliabili
43. ed by misconfiguration on the routers Figure 7 9 illustrates such a problem Network Experiencing an EIGRP Neighbor Problem Because Mismatched AS Numbers In the network shown in Figure 7 9 RTR A and RTR B are in the EIGRP AS number of 1 and the proper network numbers have been configured however no EIGRP neighbor relationship is formed between RTR A and RTR B Begin by checking the configuration of RTR A and RTR B in Example 7 7 Configurations for RTR A and RTR B in Figure 7 9 RTR B show running config interface serial 0 IP address 10 1 1 1 255 255 255 0 router eigrp 11 network 10 0 0 0 RTR A show running config Interface serial 0 IP address 10 1 1 2 255 255 255 0 router eigrp 1 network 10 0 0 0 You should notice the misconfiguration immediately RTR B s Serial 0 interface is con figured to be in EIGRP AS number 11 while RTR A s Serial 0 is configured to be in EIGRP AS number 1 Because the AS numbers don t match across the link no EIGRP neighbor relationship will be formed To resolve this problem simply configure both routers with the same EIGRP AS number as shown in Example 7 8 In this example both routers will be configured to be in EIGRP AS 1 Configuring Both Routers with the Same EIGRP AS Numbers RTR A router eigrp 1 network 10 0 0 0 RTR B router eigrp 1 network 10 0 0 0 240 Chapter 7 Troubleshooting EIGRP EIGRP Neighbor Problem Cause Stuck in Active Sometimes
44. ent in the network When the device in the core network is trying to ping or traceroute to the 172 16 40 0 network the packets are looping between Router A and Router B Troubleshooting EIGRP Route Summarization 279 Figure 7 31 EIGRP Network Diagram Too Much IP Address Summarization Summary route 172 16 0 0 16 lt q SO e2 __z A 192 168 2 1 24 B wy 192 168 3 1 24 7 lt 192 168 2 2 24 Default route 0 0 0 0 0 0 0 0 Core Network Network 172 16 1 0 24 172 16 14 0 24 Example 7 56 shows Router A s routing table for 172 16 40 0 Example 7 56 Router A Routing Table for 172 16 40 0 Router A show ip route 172 16 40 0 Routing entry for 172 16 0 0 16 Known via EIGRP 1 distance 90 metric 409600 type internal Last update from 192 168 2 2 on SerialO 00 20 25 ago Routing Descriptor Blocks x 192 168 2 2 from192 168 2 2 00 20 25 ago via Serial 0 Route metric is 409600 traffic share count is 1 Total delay is 6000 microseconds minimum bandwidth is 10000 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 The routing entry in Router A shows the summary route of 172 16 0 0 16 coming from Router B Therefore Router A forwards the packet to Router B However Router B sends the packet right back to Router A because Router B doesn t have the route for 172 16 40 0 it has only the default route pointing back to Router A This causes the routing loop between Router A and
45. er eigrp 1 network 172 16 0 0 access list 101 deny eigrp any any access list 101 permit ip any any dialer list 1 protocol ip list 101 ip route 172 16 1 255 255 255 128 172 16 3 1 200 From the configuration the backup is done through the floating static route at the end of the configuration When the primary interface Serial 0 is down the primary EIGRP route goes away and the floating static route is installed in the routing table that uses the BRI port The dialer list is tied with access list 101 which initiates the dial with any IP packet except for EIGRP hellos This will not cause the BRI link to continuously dial because of EIGRP hello packets In this scenario when the primary link goes down the BRI link comes up and passes traffic because of the floating static route The network administrator is trying to fix the link problem in doing so the network administrator reloaded Router B When Router B came back up the primary link also came up The problem is that now even when the primary link came back up the BRI link is still up and the traffic still is passing through BRI port Troubleshooting EIGRP Dial Backup Problem 289 On Router A you must verify that the routing table entry for the interesting traffic is correct Example 7 68 shows the output of show ip route 172 16 4 0 on Router A Example 7 68 Routing Table for 172 16 4 0 Router A show ip route 172 16 4 0 Routing entry for 172 16 4 0 25 Known via st
46. esting traffic that keeps the backup dialer link up Figure 7 36 Network Susceptible to EIGRP Dial Backup Problems 172 16 2 1 24 eres 172 16 2 2 24 ZAD Zp SO 2 E0 yn Sof eee E0 A B r Bri 0 172 16 1 1 25 172 16 3 1 24 Bri 0 172 16 3 2 24 172 16 4 1 25 288 Chapter 7 Troubleshooting EIGRP Example 7 67 As Figure 7 36 illustrates Router A and Router B are connected by a T1 line as the primary link The ISDN backup serves as the backup link if the primary link fails Example 7 67 shows the configurations for Routers A and B Configurations for Routers A and B in Figure 7 36 Router A isdn switch type basic 5ess interface ethernet 0 ip address 172 16 1 1 255 255 255 128 interface serial 0 ip address 172 16 2 1 255 255 255 0 interface bri 0 ip address 172 16 3 1 255 255 255 0 encapsulation ppp dialer map ip 172 16 3 2 name Router B broadcast 1234567 ppp authentication chap dialer group 1 router EIGRP 1 network 172 16 0 0 access list 101 deny eigrp any any access list 101 permit ip any any dialer list 1 protocol ip list 101 ip route 172 16 4 255 255 255 128 172 16 3 2 200 Router B isdn switch type basic 5ess interface ethernet 0 ip address 172 16 4 1 255 255 255 128 interface serial 0 ip address 172 16 2 2 255 255 255 0 interface bri 0 ip address 172 16 3 2 255 255 255 0 encapsulation ppp dialer map IP 172 16 3 1 name Router_A broadcast 3456789 ppp authentication chap dialer group 1 rout
47. from Serial1 2 Router E to re spond to the query The next step is to go to Router E to see the status of the active route 20 2 1 0 24 and to find out why Router E is not replying to the query Figure 7 15 shows the status of the active route on Router E 246 Chapter 7 Troubleshooting EIGRP Figure 7 13 Active Route Status on Router B for Troubleshooting EIGRP Stuck in Active Example 20 2 1 0 24 Ee zz 10 1 2 0 24 __ 2 j T9 z g2 z 2 ge dln es cw t i 10 1 1 0 24 1 10 1 3 0 24 10 1 4 0 24 2 2 Router B show ip eigrp topology active D y IP EIGRP Topology Table for AS 1 ID 10 1 3 1 A 20 2 1 0 24 1 successors FD is Inaccessible 1 1 replies active 00 01 23 query origin Successor Origin via 10 1 1 1 Infinity Infinity Serial1 0 10 1 5 0 24 Remaining replies via 10 1 3 2 r Serial1 2 P Pee UE E Figure 7 14 Active Route Status on Router D for Troubleshooting EIGRP Stuck in Active Example 20 2 1 0 24 A Gf zz 10 1 2 0 24 __ 2 j T9 n SS Se SE cael a es C y U r 10 1 1 0 24 1 10 1 3 0 24 10 1 4 0 24 Router D show ip eigrp topology active oe IP EIGRP Topology Table for AS 1 ID 10 1 4 2 A 20 2 1 0 24 1 successors FD is Inaccessible Q 1 replies active 00 01 43 query origin Successor Origin via 10 1 3 1 Infinity Infinity Serial1 0 10 1 5 0 24 via 10 1 4 1 Infinity Infinity Seriali 1 serno 146 Remaining replies via 10 1 5 2 r Serial1 2 Troubleshooting EI
48. g EIGRP According to the troubleshooting flowchart in Figure 7 5 the three causes of getting the EIGRP neighbor not on common subnet error message are the following The IP address has been misconfigured on interfaces The primary and secondary IP addresses of the neighboring interface don t match A switch or hub between the EIGRP neighbor connection is misconfigured or is leaking multicast packet to other ports Misconfiguration of the IP Address on the Interfaces Sometimes an EIGRP neighbor that is not on a common subnet with other EIGRP neigh bors is simply the result of misconfiguring the IP address on the interfaces For example the network administrator might mistype IP address 192 168 3 1 255 255 255 252 as 192 168 3 11 255 255 255 252 which causes EIGRP to complain about the neighbor not being on a common subnet Primary and Secondary IP Addresses of the Neighboring Interface Don t Match As mentioned in Chapter 6 Understanding Enhanced Interior Gateway Routing Protocol EIGRP EIGRP sources the hello packet from the primary address of the interface If the primary network address on one router is used as a secondary network address on the second router and vice versa no neighbor relationship will be formed and the routers will complain about the neighbor not being on a common subnet Figure 7 6 illustrates such a scenario Figure 7 6 Network Topology Vulnerable to EIGRP Neighbor Problems Because of Pri
49. g EIGRP Troubleshooting EIGRP Route Summarization Summarization is extremely important in a well designed EIGRP network Summarization is one of the few weapons to prevent stuck in active problems Most summarization problems are the result of a misconfiguration of the router Figure 7 29 shows a flowchart for trouble shooting an EIGRP summarization problem Figure 7 29 Flowchart for Troubleshooting EIGRP Summarization Route Problem EIGRP doesn t send summary routes There must be an active subnet within the range of the No gt Summary route in the routing table before the summary route can be advertised Is a subnet within the range of the summary route present in the routing table Yes Is the summary route configured with a prefix mask that covers the specific routes in the routing table Is the summary route No properly configured Yes Call TAC Possible bug present EIGRP Summarization Route Problem Cause Subnetworks of Summary Route Don t Exist in Routing Table Consider the case shown in Figure 7 30 in which Router A is configured to send out a summary route of 172 16 80 0 255 255 240 0 on its Ethernet 0 interface to Router B Example 7 52 shows the configuration of Router A However the next hop router is not seeing the route and the 172 16 80 0 255 255 240 0 route is not in the router s topology table Example 7 53 shows a snaps
50. ghbor changes that you can find in the EIGRP log along with the meaning and required action to fix the problem based on the log message Troubleshooting EIGRP Neighbor Relationships 229 Table 7 1 Neighbor Changes Documented in the EIGRP Log Log Message Meaning Action for Troubleshooting NEW Indicates that a new neighbor has No action is required ADJACENCY been established PEER Indicates that the other neighbor No action is required on the router RESTARTED initiates the reset of the neighbor that is getting the message Gather relationship The router getting the EIGRP neighbor log information on message is not the one resetting the the other neighbor neighbor HOLD TIME Indicates that the router has not Because this is a packet loss problem EXPIRED heard any EIGRP packets from the check for a Layer 2 problem Trouble neighbor within the hold time limit shoot by using the flowchart shown in Figure 7 2 RETRY LIMIT Indicates that EIGRP did not receive Troubleshoot using the flowchart EXCEEDED the acknowledgement from the shown in Figure 7 3 neighbor for EIGRP reliable packets and that EIGRP already has tried to retransmit the reliable packet 16 times without any success ROUTE Indicates that the EIGRP neighbor is No action is needed This is normal FILTER resetting because there is a change in behavior in EIGRP which needs to CHANGED the route filter distribute list reset the neighbor when the route filter co
51. he update for the 150 150 0 0 16 route from both OSPF and RIP The router installs the OSPF route because OSPF has a lower administrative distance than RIP Therefore if the route is showing up as an OSPF route the router will not redistribute this route into EIGRP In other words the router will redistribute only RIP routes that are showing in the routing table into the EIGRP domain The resolve this problem you must make Router A install the RIP route instead of the OSPF route One way to do this is to configure a distribute list under OSPF to not install the 150 150 0 0 16 route as demonstrated in Example 7 60 Configuring a Distribute List Under OSPF to Not Install the 150 150 0 0 16 Route router OSPF 1 network 172 16 0 0 0 0 255 255 area 0 distribute list 1 out access list 1 deny 150 150 0 0 0 0 255 255 access list 1 permit any Troubleshooting EIGRP Redistribution Problems 283 Example 7 61 Example 7 62 With the distribute list in place Router A s routing table for the 150 150 0 0 16 will now show the results in Example 7 61 Routing Table for 150 150 0 0 16 After Configuring the Distribute List in Example 7 60 Router A show ip route 150 150 0 0 255 255 0 0 Routing entry for 150 150 0 0 16 Known via RIP distance 120 metric 4 Redistributing via RIP Last update from 172 16 3 2 on Serial 0 Routing Descriptor Blocks 172 16 3 2 from 172 16 3 2 00 00 23 ago via Serial 0 Route metric is 4 traff
52. hen Getting Neighbor Log RETRY LIMIT EXCEEDED Getting EIGRP neighbor log Retry Limit Exceeded I Yes High CPU utilization on router Check incorrect interface access list or Layer 1 Layer 2 problem Check switch between the link Check interface errors Check with WAN connection provider Bad Interface change hardware Ping neighbor interface with small 100 byte packets and then with large 1400 1500 byte packet Success No Yes Routing problem The next hop IP address of the EIGRP neighbor does not correspond to the actual physical connection Check for miscon figuration on the router Troubleshoot from a routing perspective Check routing table entry for neighbor interface IP address Neighbor IP address with correct next hop address in routing table No Yes Repeat test from neighbor router Figure 7 4 Network Topology Vulnerable to an EIGRP Neighbor Problem Because of a Unidirectional Link WAN Cloud RTRA RTR B ED Ca In Figure 7 4 Routers RTR A and RTR B are connected by a WAN connection The circuit from RTR A to RTR B is fine but the circuit from RTR B to RTR A is broken The results from the show ip eigrp neighbor command on RTR A will not show anything because RTR B s EIGRP hello packet can t make it to RTR A Example 7 1 shows the output from show ip eigrp neighbor on RTR B 232 Chapter 7 Troublesh
53. hot of the router s routing table Troubleshooting EIGRP Route Summarization 277 Figure 7 30 Example 7 52 Example 7 53 Network Diagram for Case Study on EIGRP Summarization Route Problem Summary route 172 16 80 0 255 255 240 0 lt gt eS ip T Ren 192 168 3 2 24 Eo 192 168 3124 Eo 92 168 3 2 Configuration of Router A in the Example Shown in Figure 7 30 Router_A interface ethernet 0 ip address 192 168 3 1 255 255 255 0 ip summary address EIGRP 1 172 16 80 0 255 255 240 0 interface Serial 0 ip address 192 168 1 2 255 255 255 0 interface Serial 1 ip address 192 168 2 2 255 255 255 0 router EIGRP 1 network 192 168 1 1 0 network 192 168 2 0 network 192 168 3 0 Routing Table Snapshot Router A show ip route 192 168 1 0 24 is directly connected Serial 0 192 168 2 0 24 is directly connected Serial 1 192 168 3 0 24 is directly connected Ethernet 172 16 99 0 24 90 409600 via 192 168 1 1 Serial 172 16 97 0 24 90 409600 via 192 168 1 1 Serial 172 16 79 0 24 90 409600 via 192 168 1 1 Serial 172 16 70 0 24 90 409600 via 192 168 1 1 Serial 172 16 103 0 24 90 409600 via 192 168 1 1 Serial 0 172 16 76 0 24 90 409600 via 192 168 1 1 Serial 172 16 98 0 24 90 409600 via 192 168 1 1 Serial 25 O 0 gt 09 In the configuration shown in Example 7 52 the summary route is configured to be 172 16 80 0 255 255 240 0 by using the command
54. iability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 1 172 16 2 2 Seriali from 172 16 2 2 Send flag is 0x0 Composite metric is 2707456 2195456 Route is Internal Vector metric Minimum bandwidth is 1544 Kbit Total delay is 41000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 2 The output in Example 7 32 now shows 172 16 3 2 as the next hop to Router C which is the optimal path to the 172 16 5 0 24 network Also compare the topology table shown in Example 7 30 and Example 7 32 The EIGRP metric coming from the neighbor 172 16 3 2 has been reduced from the metric of 2 795 456 to 2 195 456 This reduction of metric of 600 000 is the result of removing the offset list As this case study demonstrates it is impor tant that you scrutinize the configuration when abnormal behavior occurs When opening a case with Cisco s TAC be sure to provide router configuration whenever possible 264 Chapter 7 Troubleshooting EIGRP Troubleshooting EIGRP Route Installation The previous section discusses the problems that EIGRP routers have when advertising routes to its neighbors This section discusses troubleshooting problems when EIGRP doesn t install the routes in the routing table The most common causes of this problem are as follows Auto or manual summarization configured Higher administrative distance Duplicate router IDs The following sections detail the causes of
55. ic share count is 1 Because the routing table in Router A shows the 150 150 0 0 16 route as a RIP route redistribution into EIGRP takes place and the EIGRP topology table in Router A now shows the results in Example 7 62 EIGRP Topology Table for 150 150 0 0 16 After Configuring the Distribute List in Example 7 60 Router A show ip eigrp topology 150 150 0 0 255 255 0 0 IP EIGRP topology entry for 150 150 0 0 16 State is Passive Query origin flag is 1 1 Successor s FD is 281600 Routing Descriptor Blocks 0 0 0 0 from RIP Send flag is 0x0 Composite metric is 281600 0 Route is External Vector metric Minimum bandwidth is 10000 Kbit Total delay is 1000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 0 External data Originating router is 172 16 3 1 this system AS number of routes is 0 External protocol is RIP external metric is 4 Administrator tag is 0 The topology table shows that route 150 150 0 0 16 is getting redistributed into EIGRP with the external routing protocol being RIP The originating router is 172 16 3 1 which is Router A Consider another case in which the network setup is shown in Figure 7 34 The routes in the OSPF domain fails to be redistributed into the EIGRP domain 284 Chapter 7 Troubleshooting EIGRP Figure 7 34 Network Setup of Case Study for OSPF to EIGRP Route Redistribution Problem EIGRP Domain 172 16 2 1 24 OSPF Domain Eo Gee
56. ip summary address eigrp 1 172 16 80 0 255 255 240 0 This summary route covers the network address range from 172 16 80 0 to 172 16 95 255 From the routing table shown in Example 7 53 notice that no routes fit between the range of 172 16 80 0 to 172 16 95 255 Therefore if no subnetworks of the configured summary route are present in the routing table the router doesn t generate the summary route The solution to this problem is to configure an interface that falls in the 172 16 80 0 255 255 240 0 range You can configure a loopback interface with address 172 16 81 1 255 255 255 0 to generate the summary route configured on Ethernet 0 Example 7 54 shows the changed configuration in Router A that will fix this manual summarization problem 278 Chapter 7 Troubleshooting EIGRP Example 7 54 Example 7 55 Changed Configuration of Router A to Fix the Manual Summarization Problem Router_A interface loopback 0 ip address 172 16 81 1 255 255 255 0 interface Ethernet 0 ip address 192 168 3 1 255 255 255 0 ip Summary address EIGRP 1 172 16 80 0 255 255 240 0 interface Serial 0 ip address 192 168 1 2 255 255 255 0 Interface Serial 1 ip address 192 168 2 2 255 255 255 0 router EIGRP 1 network 172 16 0 0 network 192 168 1 0 network 192 168 2 0 network 192 168 3 0 After the configuration change the routing table on Router A shows the manual summarization route of 172 16 80 0 255 255 240 0 as shown in Example 7 55
57. issues Yes Yes Yes Go to remote router Problem is not on the Probl ith ribute List Router won t send out local router See next section on 7 a pak li ute Gra ii specific route if manual Troubleshooting EIGRP Route Installation De CISUIPULEAISEDY COTTECUNG NS or auto summarization is configuration enabled EIGRP Is Not Advertising Routes to Its Neighbors Cause Distribute List Figure 7 19 shows a network in which EIGRP is not advertising routes to its neighbor because of a distribute list problem Example 7 14 shows the configurations for Routers A and B in this network Figure 7 19 EIGRP Network Not Advertising Routes to Its Neighbors Because of a Misconfigured Distribute List 10 1 1 2 24 EO Ba 80 10 1 1 1 24 so i A D ow 172 16 3 33 28 Update rejected Sending update by RouterA 192 168 3 0 24 192 168 3 21 28 252 Chapter 7 Troubleshooting EIGRP Example 7 14 Configurations for Routers A and B in Figure 7 19 Router A interface ethernet 0 ip address 172 16 3 1 255 255 255 0 interface serial 0 ip address 10 1 1 1 255 255 255 0 router eigrp 1 network 172 16 0 0 network 10 0 0 0 Router B interface ethernet 0 ip address 192 168 3 17 255 255 255 240 interface serial 0 ip address 10 1 1 2 255 255 255 0 router eigrp 1 network 192 168 3 0 network 10 0 0 0 distribute list 1 out access list 1 permit 192 168 3 160 0 0 0 15 The p
58. ive command This command shows what routes are currently active how long the routes have been active and which neighbors have and have not replied to the query From the output you can determine which neighbors have not replied to the query and you can track the query path and find out the status of the query by hopping to the neighbors that have not replied Example 7 9 shows sample output from the show ip eigrp topology active command Sample Output of show ip eigrp topology active Command Router show ip eigrp topology active IP EIGRP Topology Table for AS 1 1ID 10 1 4 2 A 20 2 1 0 24 1 successors FD is Inaccessible Q 1 replies active 00 01 43 query origin Successor Origin via 10 1 3 1 Infinity Infinity Serial1 0 via 10 1 4 1 Infinity Infinity Serial1 1 serno 146 Remaining replies Via 10 1 5 2 rf Serial1 2 As the output in Example 7 9 indicates the route for 20 2 1 0 is in active state and has been active for minute and 43 seconds query origin is Successor Origin which means that this route s successor sends the query to this router At this point it has gotten replies from 10 1 3 1 and 10 1 4 1 the reply is infinity which means that these two routers also don t know about the route 20 2 1 0 The most important output of the show ip eigrp topology Troubleshooting EIGRP Neighbor Relationships 243 active command is the Remaining replies section From the output of Example 7 9 this router shows
59. known to the neighbors The problem is that if there are no query boundaries EIGRP potentially can ask every router in the network for a lost route When EIGRP first queries its neighbor a stuck in active timer starts By default the timer is three minutes If in three minutes EIGRP doesn t receive the query response from all its neighbors EIGRP declares that the route is stuck in active state and resets the neighbor that has not responded to the query Figure 7 10 illustrates the query process of EIGRP when a route is lost Troubleshooting EIGRP Neighbor Relationships 241 Figure 7 10 Zllustration of EIGRP Query Process When a Route Is Lost In Figure 7 10 Router A lost its Ethernet interface Because it doesn t have a feasible successor the route becomes active and Router A queries its neighbors Router B and Router C Now Router B doesn t know how to reach the lost network so it asks its neighbors Router D and Router E Similarly Router C asks its neighbors Router F and Router G Because Routers D E F and G also don t know how to reach the lost network they query the downstream neighbors At this point the edge of the network is reached and the edge router doesn t have any more neighbors to query The edge router then replies back to Routers D E F and G Those routers reply back to Routers B and C and finally to Router A The query process then stops Figure 7 10 shows the cascade effect of the EIGRP query process
60. mary and Secondary IP Address Mismatch Routers outers Primary 10 1 1 1 24 Primary 10 1 1 2 24 Secondary 50 1 1 1 24 Secondary 50 1 1 2 24 Only Address 50 1 1 3 24 ou Routen Troubleshooting EIGRP Neighbor Relationships 235 In Figure 7 6 Router A and Router B have a primary address in the 10 1 1 0 24 network range while Router C has an address range of 50 1 1 0 24 configured When Router A or Router B sends out the EIGRP hello packet the source of the hello packet will be either 10 1 1 1 or 10 1 1 2 depending on which router sends out the hello When Router C receives the hello packet from Router A or Router B it notices that the source is from the 10 1 1 0 network Because Router C has an IP address of 50 1 1 3 configured on the interface Router C will not process the hello packet from Router A or Router B because they are from a different network Therefore no neighbor relationship is formed from Router C to either Router A or Router B The solution for this example is to match all the IP addresses on the segment to the primary address space For the network in Figure 7 6 you need to configure Router C to be in the primary address space of 10 1 1 0 24 Switch or Hub Between EIGRP Neighbor Connection Is Misconfigured or Is Leaking Multicast Packets to Other Ports If the IP address configuration is correct on the interface between EIGRP neighbors you might want to check the configuration on the switch or the hub tha
61. matically increase the likelihood of an EIGRP stuck in active problem The best practice is to readdress the IP address scheme One region should take only a block of IP addresses this way the core routers would be capable of summarizing the routes into the core resulting in a reduced routing table in the core The routers and the query would be contained only in one region Figure 7 17 shows an improved and more scalable EIGRP network design 250 Chapter 7 Troubleshooting EIGRP Figure 7 17 Scalable EIGRP Network Design Improvement on Network in Figure 7 16 eS _ lt r ee ZA 7 0 0 0 UT gt Core lt gt Core A 2 0 0 0 3 0 0 0 Core gj ae my bas 1 1 1 0 2 7 vA 1 1 4 0 U E EI Fa ace 2S ow as t y l H 2 2 1 0 2 2 3 0 UD Z so i C3 oT 2 2 2 0 Comparing Figures 7 16 and 7 17 you can see that the network presented in Figure 7 17 is more structured The Core router region takes only the 1 0 0 0 block of IP addresses the Core region 4 takes only the 2 0 0 0 block and Core 3 region takes only the 3 0 0 0 block of IP addresses This enables the three core routers to summarize their routes into the core If the Ethernet network of 3 3 3 0 flaps in the Core 3 region the query would be bounded only in the Core 3 region and would not travel the entire network to affect all the routers in the network Summarization and hierarchy are the best design practices for a large scale EIGRP network Troubleshooti
62. mmand under router EIGRP is changed and to resynchronize the EIGRP topology table between neighbors INTERFACE Indicates that the EIGRP neighbor is No action is needed This is normal DELAY resetting because there is a manual behavior in EIGRP which needs to CHANGED configuration change in the delay reset the neighbor when the delay parameter on the interface parameter is changed INTERFACE Indicates that the EIGRP neighbor is No action is needed This is normal BANDWIDTH resetting because there is a manual behavior in EIGRP which needs to CHANGED configuration change in the interface reset the neighbor when the band bandwidth on the interface width parameter is changed STUCK IN Indicates that the EIGRP neighbor is Troubleshoot from the stuck in active ACTIVE resetting because EIGRP is stuck in point of view Refer to the section active state The neighbor getting reset is the result of stuck in active EIGRP Neighbor Problem Cause Stuck in Active 230 Chapter 7 Troubleshooting EIGRP Figure 7 2 Flowchart for Troubleshooting EIGRP Neighbor Relationship When Getting Neighbor Log Message HOLD TIME EXPIRED Getting EIGRP neighbor log Hold Time Expired T Yes Perform Debug EIGRP Packet Hello Is the router sending or receiving hello packet Ygs Ping interface with small 100 byte packets and then with large 1400 1500 byte packet Success Check EIGRP configuration Mak
63. mple 7 3 Router A B and C Configurations for the Network in Figure 7 7 Router A interface serial 0 ip address 10 1 1 2 255 255 255 128 interface serial 1 ip address 10 1 3 1 255 255 255 0 Router B interface serial 0 ip address 10 1 1 1 255 255 255 0 interface ethernet 0 ip address 10 1 2 1 255 255 255 0 Router C interface ethernet 0 ip address 10 1 2 2 255 255 255 0 interface serial 0 ip address 10 1 3 2 255 255 255 0 Notice the mismatched mask on the serial interface of Router A and Router B Router A has a mask of 255 255 255 128 while Router B has a mask of 255 255 255 0 on Serial 0 Initially EIGRP has no problem forming the neighbor between Router A and Router B because 10 1 1 1 and 10 1 1 2 are in the same subnet The problem occurs when a neighbor relationship is established and Router A and Router B begin to exchange EIGRP topology tables and install routes based on the EIGRP topology table as demonstrated in Example 7 4 Troubleshooting EIGRP Neighbor Relationships 237 Example 7 4 Routing Tables from Router B and Router C Router B show ip route Codes C connected S static I IGRP R RIP M mobile B BGP D EIGRP EX EIGRP external O OSPF IA OSPF inter area N1 OSPF NSSA external type 1 N2 OSPF NSSA external type 2 E1 OSPF external type 1 E2 OSPF external type 2 E EGP i IS IS L1 IS IS level 1 L2 IS IS level 2 ia IS IS inter area candidate defaul
64. must change the administrative distance of the routing proto cols so that external EIGRP routes are preferred To do so use the distance command to manipulate the administrative distance of a routing protocol The configuration of Router B to fix this problem is shown in Example 7 39 Example 7 39 Configuration Change on Router B to Fix the Route Installation Problem Because of Higher Administrative Distance Router B interface ethernet 0 ip address 172 16 2 1 255 255 255 0 interface serial 0 192 168 1 1 255 255 255 0 interface serial 1 192 168 2 1 255 255 255 0 router eigrp 1 network 172 16 0 0 network 192 168 1 0 network 192 168 2 0 router rip network 172 16 0 0 network 192 168 2 0 distance 180 192 168 2 2 255 255 255 255 The distance command shown in Example 7 39 sets the RIP administrative distance to 180 for any updates coming from 192 168 2 2 This allows the external EIGRP routes administrative distance of 170 coming from Router C to be preferred over RIP routes Example 7 40 shows the result Example 7 40 Routing Table of Router B Now Showing Summary Route Coming from Router C Router_B show ip route 150 150 0 0 Routing entry for 150 150 0 0 16 Known via eigrp 1 distance 90 metric 2195456 type internal Redistributing via eigrp 1 Last update from 192 168 1 2 on Serial 00 26 14 ago Routing Descriptor Blocks 192 168 1 2 from 192 168 1 2 00 26 14 ago via Serial Route metric is 2195456 tr
65. ng EIGRP Route Advertisement Sometimes EIGRP has issues with route advertisement This section discusses methods for troubleshooting EIGRP route advertisement problems which can be categorized as follows EIGRP is not advertising routes to neighbors when the network administrators think that it should EIGRP is advertising routes to neighbors when the network administrators think that it shouldn t e EIGRP is advertising routes with a metric that is not understood by the network administrators Troubleshooting EIGRP Route Advertisement 251 EIGRP Is Not Advertising Routes to Neighbors When the Network Administrators Think That It Should This section discusses methods for troubleshooting issues related to EIGRP not advertising routes to the neighbors Figure 7 18 shows a flowchart documenting how to troubleshoot this issue Figure 7 18 Troubleshooting Flowchart for Problems Related to EIGRP Not Advertising Routes to Its Neighbors EIGRP not advertising routes to its neighbors Perform Show IP EIGRP Neighbor Has the neighbor relationship being established Neighbor Problem See section on No Troubleshooting EIGRP Neighbor Problem Issues with Auto or Manual Summarization Check Distribute List Misconfigured Distribute List Perform Debug IP EIGRP See EIGRP routes being advertised No Check for Split Horizon
66. oblems The flow charts presented for each category of problems give you good direction on the trouble shooting path When doing a debug on the router keep in mind that any debug has the potential to overwhelm the router and the debug must be done when the router has low CPU utilization and preferably during a maintenance window A great deal of the trouble shooting can be done by just doing the show commands as pointed out in this chapter Take the time to understand the details of the output of the various show commands introduced This way when the problem happens you can quickly and swiftly identify the problem and fix it
67. on The offset list command adds an offset value to the routing metrics It s a way to manipulate the routing metric for certain routes thereby altering the route selection for a particular routing protocol Figure 7 23 illustrates the network setup for the unexpected metric value problem Figure 7 23 EIGRP Network Susceptible to EIGRP Advertisement Problems Because of Unexpected Metric Values 172 16 6 1 24 E0 Pn SO j za S1 B 172 16 1 1 24 172 16 4 1 24 B 172 16 2 1 24 172 16 4 2 24 172 16 1 1 24 PA 172 16 2 2 24 oe SO ae A S1 Cc 172 16 3 1 24 6 9 1 172 16 3 2 24 EO E0 Troubleshooting EIGRP Route Advertisement 261 Example 7 29 shows the configurations for the routers in the EIGRP network shown in Figure 7 23 Example 7 29 Configurations for Routers A B and C in Figure 7 23 Example 7 30 Router A interface ethernet 0 ip address 172 16 1 1 255 255 255 0 interface serial 0 ip address 172 16 2 1 255 255 255 0 interface serial 1 ip address 172 16 3 1 255 255 255 0 router eigrp 1 network 172 16 0 0 Router B interface ethernet 0 ip address 172 16 6 1 255 255 255 0 interface serial 0 ip address 172 16 2 2 255 255 255 0 interface serial 1 ip address 172 16 4 1 255 255 255 0 router eigrp 1 network 172 16 0 0 Router C interface ethernet 0 ip address 172 16 5 1 255 255 255 0 interface serial 0 ip address 172 16 4 2 255 255 255 0 interface serial 1 ip address 172 16 3 2 255 255 255
68. ooting EIGRP Example 7 1 Example 7 2 show ip eigrp neighbors Command Output on RTR B RtrB show ip eigrp neighbors IP EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq sec ms Cnt Num 1 10 88 18 2 SO 14 00 00 15 0 5000 4 RTR B shows RTR A as a neighbor because RTR A s EIGRP hello packet has no problem reaching RTR B From the output of the show command the SRTT is at 0 ms the retransmission timeout RTO timer is at 5000 ms and the Q count is at 4 and is not decrementing These three numbers give the biggest clue that this is a unidirectional link problem The following is the meaning of SRTT RTO and Q count Smooth round trip time SRTT The number of milliseconds it takes for an EIGRP packet to be sent to this neighbor and for the local router to receive an acknowledgment of that packet Retransmission timeout RTO in milliseconds The amount of time that the software waits before retransmitting a packet from the retransmission queue to a neighbor Qcount The number of EIGRP packets Update Query and Reply that the software is waiting to send Referring to Example 7 1 the fact that the SRTT timer is 0 indicates that no acknowledge ment packets are being received The Q count is not decrementing which indicates that the router is trying to send EIGRP packets but no acknowledgement is being received RTR B will retry 16 times to resend the packet eventually
69. ork 172 16 0 0 network 10 0 0 0 Router B interface ethernet 0 ip address 192 168 130 1 255 255 255 0 continues 258 Chapter 7 Troubleshooting EIGRP Example 7 25 Example 7 26 Configuration of Router A and Router B for the Example Shown in Figure 7 19 Continued interface serial 0 ip address 10 1 1 2 255 255 255 0 router eigrp 1 network 192 168 130 0 network 10 0 0 0 ip route 192 168 1 0 255 255 255 0 ethernet 0 ip route 192 168 2 0 255 255 255 0 ethernet 0 ip route 192 168 3 0 255 255 255 0 ethernet 0 ip route 192 168 4 0 255 255 255 0 ethernet 0 ip route 192 168 127 0 255 255 255 0 ethernet 0 The problem is that without inserting the redistribute static command under the router eigrp command in Router B Router B automatically redistributes all the 127 static routes configured to Router A This can cause unnecessary routes being advertised inadvertently throughout the entire network The cause of the problem is that the static routes are configured with the outbound interface In this case the router thinks that all the static routes are directly connected to the Ethernet 0 interface These Ethernet interfaces also are covered under the router EIGRP process by the network 192 168 130 0 command Because Ethernet 0 is con sidered to run EIGRP all the networks connected to it by a static route also are considered to belong to the EIGRP process The router then advertises all these static routes even tho
70. ow ip eigrp topology active com mand the router can use any combination of these methods to represent neighbors that have not yet replied to the queries as demonstrated in Example 7 11 Output of show ip eigrp topology active That Shows a Combination Representation of Neighbors That Have Not Replied to the Queries Router show ip eigrp topology active IP EIGRP Topology Table for AS 110 1D 175 62 8 1 A 11 11 11 0 24 1 successors FD is Inaccessible 1 replies active 00 02 06 query origin Successor Origin via 1 1 1 2 Infinity Infinity r Serial1 serno 171 via 10 1 1 2 Infinity Infinity Serial1 1 serno 173 Remaining replies via 10 1 5 2 l Serial1 2 In Example 7 11 the neighbors that have not replied to the queries are 1 1 1 2 and 10 1 5 2 Only one of the nonreplying neighbors 10 1 5 2 is listed under the Remaining replies section the other neighbor 1 1 1 2 that has not replied is listed with the other replying neighbor To summarize when issuing the show ip eigrp topology active com mand the most important part to look for is the neighbors that have not replied to the query To look for such a neighbor look for neighbors that have the r next to their interface IP addresses 244 Chapter 7 Troubleshooting EIGRP Methodology for Troubleshooting the Stuck in Active Problem The methods for troubleshooting an EIGRP stuck in active problem and the show ip eigrp topology active command are useful only when th
71. ppear in the routing table Router A will not install any external routes that originate from Router X because external routes carry the router ID in their EIGRP update packet Router A will install internal EIGRP routes from Router X without any problem The duplicate router ID problem happens only for external routes The solution to the duplicate router ID problem is to change the IP address of the loopback interface of Router X or to change the IP address of Ethernet 0 in Router A The rule of thumb Never configure the same IP address on two places in the network Change the loopback IP address of Router X to 192 168 9 1 32 to fix this problem see Example 7 44 Troubleshooting EIGRP Route Flapping 271 The result of the IP address change in Router X is the installment of the 150 150 0 0 16 route in Router A as shown in Example 7 45 Example 7 44 Loopback IP Address Change in Router X to Avoid Duplicate Router ID Problem Router X interface Loopback 0 IP address 192 168 9 1 255 255 255 255 Example 7 45 Routing Table and EIGRP Topology Table for 150 150 0 0 16 on Router A to Verify the Fix Router_A show ip route 150 150 0 0 Routing entry for 150 150 0 0 16 Known via eigrp 1 distance 170 metric 4269056 type external Redistributing via eigrp 1 Last update from 10 1 1 2 on Serial 00 06 14 ago Routing Descriptor Blocks 10 1 1 2 from 10 1 1 2 00 06 14 ago via Seriald Route metric is 4269056 traffic share count is
72. provides you with a glimpse of EIGRP events that includes the neighbors that are updating the router with the route identified and the metric with which the neighbor updates the router Consider the network shown in Figure 7 28 Figure 7 28 EIGRP Network Susceptible to EIGRP Route Flap an Q 10 1 2 2 24 10 1 3 1 24 10 1 2 1 24 Network Cloud X 150 150 0 0 16 route originates 192 168 1 1 24 from Network Cloud X 10 1 5 1 24 10 1 1 3 24 274 Chapter 7 Troubleshooting EIGRP In Figure 7 28 a route of 150 150 0 0 16 in network cloud X gets passed to Router A from Routers B C and D Router A chooses Router C as the next hop to network 150 150 0 0 16 and puts Routers B and D as the feasible successors to the network 150 150 0 0 16 Example 7 49 shows the pertinent configuration for all four routers Example 7 49 Configurations for Routers A B C and D in Figure 7 28 Example 7 50 Router A interface ethernet 0 ip address 10 1 1 1 255 255 255 0 interface serial 0 ip address 10 1 2 1 255 255 255 0 Router B interface serial 0 ip address 10 1 2 2 255 255 255 0 interface serial 1 ip address 10 1 3 1 255 255 255 0 Router C interface ethernet 0 ip address 10 1 1 2 255 255 255 0 interface serial 0 ip address 10 1 4 1 255 255 255 0 Router D interface ethernet 0 ip address 10 1 1 3 255 255 255 0 interface serial 0 ip address 10 1 5 1 255 255 255 0 The problem happens in Rou
73. roblem is that Router A is not receiving the routes from Router B about network 192 168 3 16 Example 7 15 shows the debug output on Router B Example 7 15 debug ip eigrp Command Output on Router B Router_B debug ip eigrp IP EIGRP 192 168 3 16 28 denied by distribute list As the output in Example 7 15 reveals Router B won t advertise the 192 168 3 16 because of the distribute list configuration Looking again at the configuration in Example 7 14 you can see that the distribute list is tied to access list 1 and access list 1 has the network number misconfigured access list 1 should permit 192 168 3 16 instead of 192 168 3 160 Because 192 168 3 16 is not included in the permit statement there is an implicit deny in the access list that prevents network 192 168 3 16 being advertised The solution to this problem is to change access list 1 to permit 192 168 3 16 instead of 192 168 3 160 Changing the access list to permit 192 168 3 16 fixes the problem EIGRP Is Not Advertising Routes to Its Neighbors Cause Discontiguous Networks Using the network diagram in Figure 7 19 another issue with EIGRP not advertising the network could be manual summarization configured on the interface or autosummarization across a major network boundary as shown in Example 7 16 Example 7 16 Configurations for Routers A and B in Figure 7 19 Router A interface ethernet 0 ip address 192 168 3 33 255 255 255 240 interface serial 0 ip addre
74. s 1544 Kbit Total delay is 41000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 3 External data Originating router is 155 155 155 1 AS number of routes is 0 External protocol is OSPF external metric is 64 Administrator tag is 0 The EIGRP topology table shows that the feasible distance FD is inaccessible 4294967295 the route is an external route that has been redistributed from OSPF This means that Router B is receiving the 150 150 0 0 16 routes from Router C but is setting the FD as inaccessible because Router B is not using the EIGRP route in the routing table As a matter of fact the routing table entry in Router B is a RIP route for 150 150 0 0 16 as shown in Example 7 38 In other words when the FD is inaccessible in the EIGRP topology table the router is not using that EIGRP route in its routing table Usually the route is overridden by another routing protocol that has lower administrative distance Example 7 38 Routing Table of Router B Showing 150 150 0 0 16 Route as a RIP Route Router_B show ip route 150 150 0 0 Routing entry for 150 150 0 0 16 Known via rip distance 120 metric 5 Redistributing via rip Last update from 192 168 2 2 on Serial1 00 00 24 ago Routing Descriptor Blocks 192 168 2 2 from 192 168 2 2 00 00 24 ago via Seriali Route metric is 5 traffic share count is 1 268 Chapter 7 Troubleshooting EIGRP To fix this problem you
75. shows that EIGRP summarizes the 172 16 0 0 16 route because of autosummarization Every time autosummarization or manual summarization takes place EIGRP installs the summary route with the next hop to Null 0 This is a loop prevention mechanism for EIGRP s summary routes In this case study this is exactly what happens EIGRP does not install a route from its neighbor that falls within its summary range The solution to this problem based on this cause is more of a design issue Two places in the network must not send the same summary routes to one another In this example you configure the no auto summary command on Router B to allow Router B to accept the summary routes coming from Router C Example 7 35 shows the configuration in Router B to fix the problem Example 7 35 Configuration Change on Router B to Fix the Problem Shown in Figure 7 25 Router B interface ethernet 0 ip address 172 16 2 1 255 255 255 0 interface serial 0 192 168 1 1 255 255 255 0 interface serial 1 192 168 2 1 255 255 255 0 router eigrp 1 network 172 16 0 0 network 192 168 1 0 network 192 168 2 0 no auto summary With the configuration change in Router B the routing table shown in Example 7 36 for Router B now shows the summary route of 172 16 0 0 16 coming from Router C Example 7 36 Routing Table of Router B Now Showing Summary Route Coming from Router C Router_B show ip route 172 16 0 255 255 0 0 Routing entry for 172 16 0 0 16 Known via
76. ss 10 1 1 1 255 255 255 0 router eigrp 1 network 192 168 3 0 network 10 0 0 0 Troubleshooting EIGRP Route Advertisement 253 Example 7 16 Configurations for Routers A and B in Figure 7 19 Continued Router B interface ethernet 0 ip address 192 168 3 21 255 255 255 240 interface serial 0 ip address 10 1 1 2 255 255 255 0 router eigrp 1 network 192 168 3 0 network 10 0 0 0 The problem is that Router A is not receiving routes for the 192 168 3 16 network from Router B Example 7 17 shows the debug output on Router B Example 7 17 debug ip eigrp Command Output on Router B Router B debug ip eigrp IP EIGRP 192 168 3 16 28 don t advertise out Seriald IP EIGRP 192 168 3 0 24 do advertise out Seriald From the debug Router B shows that it is not advertising the 192 168 3 16 28 network however it is advertising only the major network of 192 168 3 0 24 to Router A Looking at the configuration of Routers A and B in Example 7 16 shows that the two routers have a discontiguous network Router A has the network of 192 168 3 32 28 in its Ethernet while Router B has another network of 192 168 3 16 28 in its Ethernet separated by a network of 10 1 1 0 24 Therefore when Router B advertises the network of 192 168 3 16 28 across a major network boundary of 10 1 1 0 it advertises only the major network of 192 168 3 0 24 to Router A instead of advertising the network of 192 168 3 16 28 When Router A receives th
77. ssage means that the primary route is gone and no feasible successor is available The router has sent out the queries to its neighbor and has not heard the reply from a particular neighbor for more than three minutes The route state is now stuck in active state A more detailed discussion about this error is in the Troubleshooting EIGRP Neighbor Relationships section Neighbor not on common subnet This message means that the router has heard a hello packet from a neighbor that is not on the same subnet as the router A more detailed discussion about this error also can be found in the Troubleshooting EIGRP Neighbor Relationships section DUAL 3 BADCOUNT Badcount means that EIGRP believes that it knows of more routes for a given network than actually exist It s typically not always seen in conjunction with DUAL 3 SIAs but it is not believed to cause any problems by itself Unequal lt route gt dndb lt metric gt query lt metric gt This message is informa tional only It says that the metric the router had at the time of the query does not match the metric that it had when it received the reply DUAL 3 INTERNAL IP EIGRP Internal Error This message indicates that there is an EIGRP internal error However the router is coded to fully recover from this internal error The EIGRP internal error is caused by software problem and should not affect the operation of the router The plan of action is to report this error to
78. st configure Router C as in Example 7 31 Removing the Offset List from Router C s Configuration Router C config term Router_C config router eigrp 1 Router_C config router no offset list 1 out 600000 serial 1 Troubleshooting EIGRP Route Advertisement 263 Example 7 32 shows the routing table and the topology table in Router A after removing the offset list configured on Router C Example 7 32 show ip route and show ip eigrp topology Command Output Verifies That Router A Is Now Taking the Optimal Routes to Reach Router C s 172 16 5 0 24 Ethernet Network Router_A show ip route 172 16 5 0 Routing entry for 172 16 5 0 24 Known via eigrp 1 distance 90 metric 2195456 type internal Redistributing via eigrp 1 Last update from 172 16 3 2 on Seriali 00 08 23 ago Routing Descriptor Blocks 172 16 3 2 from 172 16 3 2 00 08 23 ago via Seriali Route metric is 2195456 traffic share count is 1 Total delay is 21000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 Router A show ip eigrp topology 172 16 5 0 255 255 255 0 IP EIGRP topology entry for 172 16 5 0 24 State is Passive Query origin flag is 1 1 Successor s FD is 2195456 Routing Descriptor Blocks 172 16 3 2 Seriali from 172 16 3 2 Send flag is 0x0 Composite metric is 2195456 281600 Route is Internal Vector metric Minimum bandwidth is 1544 Kbit Total delay is 21000 microseconds Rel
79. successfully being redistributed from OSPF into EIGRP Troubleshooting EIGRP Dial Backup Problem Dial backup is acommon setup on the remote access routers When the primary link fails dial backup provides another means of network connection This section discusses EIGRP dial backup issues in which the router doesn t disconnect the dialer interface when the primary link comes back See the flowchart in Figure 7 35 for troubleshooting EIGRP dial backup problems Figure 7 36 shows the network setup for the case study on the EIGRP dial backup problem Troubleshooting EIGRP Dial Backup Problem 287 Figure 7 35 Flowchart for Troubleshooting EIGRP Dial Backup Problems Router won t hang up backup dialer interface when the primary link is available Check EIGRP neighbor status Is EIGRP neighbor up across primary link If dialer map is used is the broadcast keyword Configure the broadcast keyword in the dialer map statement Router won t pass EIGRP hello packet configured without it Yes Yes See section on Check the routing table for the Troubleshooting route that initiates the dial Is the EIGRP Neighbor route from the primary link No Problem is that interesting traffic is still going through the wes gt backup link Check routing through the backup link Do debug dialer and see what is the inter
80. t U per user static route o ODR P periodic downloaded static route Gateway of last resort is not set C 10 1 1 0 24 Serial 0 D 10 1 1 0 25 10 1 2 2 Router c show ip route eigrp Codes C connected S static I IGRP R RIP M mobile B BGP D EIGRP EX EIGRP external O OSPF IA OSPF inter area N1 OSPF NSSA external type 1 N2 OSPF NSSA external type 2 E1 OSPF external type 1 E2 OSPF external type 2 E EGP i IS IS L1 IS IS level 1 L2 IS IS level 2 ia IS IS inter area candidate default U per user static route o ODR P periodic downloaded static route Gateway of last resort is not set D 10 1 1 0 24 10 1 2 1 D10 1 1 0 25 10 1 3 1 When Router B sends Router A an EIGRP update Router A responds to the update with an EIGRP acknowledgement packet with a destination address of 10 1 1 1 to Router B When Router B receives the packet it forwards the ACK packet to Router C instead of processing it because Router B has a more specific route from Router C Router B has a more specific route of 10 1 1 0 25 with the next hop to 10 1 2 2 This 25 route overrides the 24 route because 25 is more specific than 24 When Router C receives the ACK packet from Router B it looks at its routing table for the 10 1 1 1 entry and the routing table points to Router A Router C then forwards the ACK packet back to Router A This creates a routing loop The packet to 10 1 1 1 loops from Router A
81. t connects the EIGRP neighbors If a single LAN hub connects the EIGRP neighbors for different LAN segment the hub passes broadcast and multicast packets to other ports between two logical LAN seg ments So the multicast EIGRP hello from LAN segment 1 will be seen on the neighbor located in LAN segment 2 if a single hub connects all the LAN devices on different LAN segments The solution is to break up the broadcast domain by using a separate hub for each LAN segment or simply configuring no eigrp log neighbor warnings under EIGRP con figuration to stop seeing the error message If a LAN switch connects the LAN devices you might want to check the configuration of the switch Make sure that the switch is not configured so that different LAN segments reside within the same VLAN Make sure that the switch is configured so that each LAN segment has its own broadcast domain and does not share its broadcast domain with other LAN segments EIGRP Neighbor Problem Cause Mismatched Masks Sometimes a simple misconfiguration on the interface subnet mask causes an EIGRP neighbor problem Figure 7 7 illustrates a network diagram for such a scenario 236 Chapter 7 Troubleshooting EIGRP Figure 7 7 Network Topology Vulnerable to EIGRP Neighbor Problems Because of Mismatched Masks gt Z Route 10 1 1 2 25 10 1 3 1 24 10 1 1 1 24 10 1 3 2 24 Routers koae 10 1 2 1 24 10 1 2 2 24 Example 7 3 shows the configuration for Routers A B and C Exa
82. ted static routes in the example The debug output on Router B shown in Example 7 27 shows that the router does not send the static routes to other EIGRP neighbors because the distribute list is configured Verification on Router B Not Sending Out Static Routes Because a Distribute List Is Configured Router B debug ip eigrp IP EIGRP 192 168 1 0 24 denied by distribute list IP EIGRP 192 168 2 0 24 denied by distribute list IP EIGRP 192 168 3 0 24 denied by distribute list IP EIGRP 192 168 4 0 24 denied by distribute list IP EIGRP 192 168 5 0 24 denied by distribute list IP EIGRP 192 168 6 0 24 denied by distribute list IP EIGRP 192 168 127 0 24 denied by distribute list The other solution to this problem is to redefine the static routes so that the next hop of the static route is an IP address instead of an interface Example 7 28 shows the change of static route configuration in Router B to fix the problem Configuration on Router B to Stop Sending Unwanted Static Routes by Reconfiguring Static Routes with the Next Hop an IP Address Instead of an Interface Router B interface ethernet 0 ip address 192 168 130 1 255 255 255 0 iinterface serial 0 ip address 10 1 1 2 255 255 255 0 router eigrp 1 network 192 168 130 0 network 10 0 0 0 distribute list 1 out ip route 192 168 1 0 255 255 255 0 192 168 130 2 ip route 192 168 2 0 255 255 255 0 192 168 130 2 ip route 192 168 3 0 255 255 255 0 192 168
83. ter A where the route timer for the route 150 150 0 0 16 in the routing table is constantly at 00 00 00 By looking at Router C the next hop to the route you can see that the route is stable and is not flapping The neighbor relationship in Router Ais also stable and the interfaces on Router A are stable with no signs of interface flapping The next step is to look at the event log in EIGRP and see which neighbor is updating Router A constantly about the route 150 150 0 0 16 Example 7 50 shows the relevant information in the EIGRP event log on Router A show ip eigrp event Command Output on Router A Router A show ip eigrp event 20 47 13 2 Rcv update dest nh 150 150 0 0 16 10 1 1 3 20 47 13 2 Metric set 150 150 0 0 16 4872198 20 47 13 2 Rcv update dest nh 150 150 0 0 16 10 1 1 3 20 47 13 2 Metric set 150 150 0 0 16 4872198 Other output in the event log exists but only the important lines are shown here To make sure that the router is constantly getting updates the show ip eigrp event command has to be done several times in succession Check whether the timer on the left side of the output is constantly changing If the timer is constantly changing this indicates that the EIGRP process is constantly calculating The EIGRP event log is read upside down with the most recent event at the top of the list and the oldest event at the bottom of the list The event log Troubleshooting EIGRP Route Flapping 275 Example 7 51
84. the TAC and have the experts decode the traceback message Have them identify the bug number and upgrade Cisco IOS Software accordingly IP EIGRP Callback callbackup_routes At some point EIGRP attempted to install routes to the destinations and failed most commonly because of the existence of a route with a better administrative distance When this occurs EIGRP registers its route as a backup route When the better route disappears from the routing table EIGRP is called back through callbackup_routes so that it can attempt to reinstall the routes that it is holding in the topology table Error EIGRP DDB not configured on interface This means that when the router s interface receives an EIGRP hello packet and the router goes to associate the packet with a DDB DUAL descriptor block for that interface it does not find one that matches This means that the router is receiving a hello packet on the interface in which doesn t have EIGRP configured Poison squashed The router threads a topology table entry as a poison in reply to an update the router set up for poison reverse While the router is building the packet that contains the poison reverse the router realizes that it doesn t need to send it For example if the router receives a query for that route from the neighbor it is currently threaded to poison 292 Chapter 7 Troubleshooting EIGRP Summary This chapter discusses methods for troubleshooting various EIGRP pr
85. the hub router Router A Example 7 20 debug ip eigrp Command Output on Router A Example 7 21 Example 7 22 Router A debug ip eigrp IP EIGRP 172 16 1 0 24 do advertise out Seriald IP EIGRP Processing incoming UPDATE packet IP EIGRP Int 172 16 3 0 24 IP EIGRP Int 172 16 4 0 24 From the debug you can see that the hub router advertises only the 172 16 1 0 24 route on Serial0 The hub router receives routes for the 172 16 3 0 24 and 172 16 4 0 24 interfaces from Router B and Router C The problem is that the hub router is not sending all the routes on Serial0 Referring to the configurations of Routers A B and C in Example 7 19 you can see that their serial interfaces are all in the same subnet but they are not physically connected Therefore the hub router receives the routes from Serial0 from Router B and Router C but won t readvertise those routes on Serial0 This follows the split horizon rule route information must not exit the router interface through which that information was received To solve the split horizon problem for EIGRP the easiest fix is to turn off split horizon for EIGRP Example 7 21 shows the correct configuration change to disable split horizon Disabling Split Horizon on the Hub Router Router A interface ethernet 0 ip address 172 16 1 1 255 255 255 0 interface serial 0 ip address 172 16 2 1 255 255 255 0 no IP split horizon EIGRP 1 router EIGRP 1 network 172 16 0 0 Example
86. to Router B from Router B to Router C and back from Router C to Router A As a result Router B won t process the ACK packet from Router A Router B will think that Router A never ACK ed the update packet and Router B will reset the neighbor after 16 retries The solution for this problem Configure the right subnet mask on Router A s Serial 0 interface to 255 255 255 0 EIGRP Neighbor Problem Cause Mismatched K Values For EIGRP to establish its neighbors the K constant value to manipulate the EIGRP metric must be the same Refer to Chapter 6 for an explanation of the K values In EIGRP s 238 Chapter 7 Troubleshooting EIGRP metric calculation the default for the K value is set so that only the bandwidth and the delay of the interface are used to calculate the EIGRP metric Many times the network administrator might want other interface factors such as load and reliability to determine the EIGRP metric Therefore the K values are changed Because only bandwidth and delay are used in calculations the remaining K values are set to a value of 0 by default However the K values must be the same for all the routers or EIGRP won t establish a neighbor relationship Figure 7 8 shows an example of this case Figure 7 8 Network Vulnerable to EIGRP Neighbor Problems Because of Mismatched K Values RTRA RTRB k z K1 1 ST Geo K2 1 K3 1 mn r K3 1 K4 1 For the network in Figure 7 8 K1 is bandwidth and K3 is delay
87. tween Router D and Router E More investigation is needed between these routers A look at Router D and Router E s router CPU utilization and memory usage doesn t show a problem Both routers CPU utilization and available memory are normal You need to look at Router D s neighbor list to see if there is a problem with the neighbors Example 7 12 shows Router D s EIGRP neighbor list 248 Chapter 7 Troubleshooting EIGRP Example 7 12 Router D s EIGRP Neighbor List RTRD show ip eigrp neighbors IP EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq sec ms Cnt Num 2 10 1 5 2 Se1 2 13 00 00 14 0 5000 1 1 10 1 3 1 Se1 0 13 01 22 54 227 1362 0 385 10 1 4 1 Se1 1 10 01 24 08 182 1140 171 From Example 7 12 notice that there is a problem in Router D with EIGRP sending a reliable packet to the neighbor with IP address of 10 1 5 2 Router E The Q count is 1 and performing the show ip eigrp neighbors command a few times in succession shows that the Q count is not decrementing The RTO counter is at its maximum value of 5000 ms This indicates that Router D is trying to send a reliable packet to Router E but Router E never acknowledges the reliable packet back to Router D Because Router E doesn t appear to have a high CPU or memory prob lem you should test the link reliability between Router D and Router E Now send five ping packets from Router D to IP address 10 1 5 2 Router
88. ty is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 7 External data Originating router is 192 168 1 1 AS number of routes is 0 External protocol is OSPF external metric is 64 Administrator tag is 0 Router B shows that it is getting the routes from Router C By looking at the external data section notice that the originating router is 192 168 1 1 which is seven hops away The original protocol that originated the route 150 150 0 0 16 is OSPF with the metric of 64 Notice that the originating router is 192 168 1 1 Looking back at the configuration of Router A in Example 7 41 notice that Router A also has an IP address of 192 168 1 1 configured on Ethernet 0 and it is the highest IP address on the router All this evidence points to a duplicate router ID problem in EIGRP that causes Router A not to install routes Because Router X and Router A have the same router ID 192 168 1 1 when Router A receives the route from Router B it looks at the external data section of the route to see who is the originating router In this case Router A sees the originating router as 192 168 1 1 which is its own router ID Router A does not put the route in its topology table because it thinks that it is the originator of the route and that by receiving the route back from other neighbors it must be a loop So to prevent a routing loop Router A does not put the route of 150 150 0 0 16 in the topology table Consequently the route does not a
89. uery origin flag is 1 1 Successor s FD is 2707456 Routing Descriptor Blocks 172 16 2 2 Serial from 172 16 2 2 Send flag is 0x0 Composite metric is 2707456 2195456 Route is Internal Vector metric Minimum bandwidth is 1544 Kbit Total delay is 41000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 2 172 16 3 2 Seriali from 172 16 3 2 Send flag is 0x0 Composite metric is 2795456 281600 Route is Internal Vector metric Minimum bandwidth is 1544 Kbit Total delay is 44437 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 1 Example 7 30 shows that Router A chooses Router B as the next hop to Router C because Router B has a better metric than Router C Looking in detail at the topology table shows that the path to Router C has more delay than the path to Router B but all the links are T1 links The interface configuration in Router C didn t show any manually configured delay value Looking at the configuration in Router C more in detail reveals the offset list configuration under router eigrp in Router C The offset list in Router C adds a metric of 600 000 to outgoing routes in Seriall This is the cause of the problem The offset values added increase the delay value when Router C sends the routes to Router A causing Router A to prefer routes from Router B The solution is to remove the offset list configured on Router C To remove the offset li
90. ugh redistribute static is not configured The solution to this problem is either to configure a distribute list that prevents the router from advertising all those static routes or to change the static routes to reference the next hop IP addresses instead of an interface This way the router will not advertise all these static routes and flood the entire network with unnecessary routes Example 7 26 shows the distribute list configured on Router B to stop sending the unwanted redistributed static routes Configuration on Router B to Stop Sending Unwanted Static Routes by Configuring Distribute List Router B interface ethernet 0 ip address 192 168 130 1 255 255 255 0 iinterface serial 0 ip address 10 1 1 2 255 255 255 0 router eigrp 1 network 192 168 130 0 network 10 0 0 0 distribute list 1 out ip route 192 168 1 0 255 255 255 0 ethernet 0 ip route 192 168 2 0 255 255 255 0 ethernet 0 ip route 192 168 3 0 255 255 255 0 ethernet 0 ip route 192 168 4 0 255 255 255 0 ethernet 0 ip route 192 168 127 0 255 255 255 0 ethernet 0 access list 1 deny 192 168 0 0 0 0 127 255 access list 1 permit any Troubleshooting EIGRP Route Advertisement 259 Example 7 27 Example 7 28 The distribute list is tied to access list 1 and access list 1 denies sending out any routes that ranges from 192 168 0 0 24 through 192 168 127 0 24 and permits sending any other routes Such a distribute list stops sending out the unwanted redistribu
91. ws the routing table in Router A for the 10 0 0 0 8 route Example 7 66 Routing Table on Router A and EIGRP Topology Table in Router B for the 10 0 0 0 8 Route to Verify the Fix Router_A show ip route 10 0 0 0 Routing entry for 10 0 0 0 8 Known via eigrp 1 distance 170 metric 2195456 type external Redistributing via eigrp 1 Last update from 172 16 1 2 on Serial 00 16 37 ago Routing Descriptor Blocks 172 16 1 2 from 172 16 1 2 00 16 37 ago via Serial Route metric is 2195456 traffic share count is 1 Total delay is 21000 microseconds minimum bandwidth is 1544 Kbit Reliability 255 255 minimum MTU 1500 bytes Loading 1 255 Hops 1 Router B show ip eigrp topology 10 0 0 0 255 0 0 0 IP EIGRP topology entry for 10 0 0 0 8 State is Passive Query origin flag is 1 1 Successor s FD is 281600 Routing Descriptor Blocks 0 0 0 0 from Redistributed Send flag is 0x0 Composite metric is 281600 0 Route is External Vector metric Minimum bandwidth is 10000 Kbit Total delay is 1000 microseconds Reliability is 255 255 Load is 1 255 Minimum MTU is 1500 Hop count is 0 External data Originating router is 172 16 2 1 this system AS number of routes is 1 External protocol is OSPF external metric is 206 Administrator tag is 0 From Example 7 66 you can see that Router A has the 10 0 0 0 8 route as EIGRP external route whereas Router B has the EIGRP topology entry for the 10 0 0 0 8 route The 10 0 0 0 8 route now has been

Troubleshooting EIGRP Neighbor Relationships

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