Chapter 8 Network Troubleshooting Part II
Contents
1. ISDN Distance time 64 or 128 kb s up to 2 Dialed slow connection Mb s PRI X 25 Volume up to 48 kb s Switched fixed capacity ATM Capacity up to 155 Mb s Permanent variable Frame Relay Capacity up to 45 Mbis Permanent variable capacity DSL Monthly subscription up to 3 Mb s Always on shared Internet Metro Ethernet Monthly subscription up to 500 Mb s Limited geographical scope Form the backbone CCNA4 13 Chapter 8 2 WAN Connection Technologies O o o e Frame Relay and ATM are examples of shared networks Because several customers are sharing the link the cost to each is generally less than the cost of a direct link of the same capacity Frame Relay may also be used for delay sensitive traffic often using QoS mechanisms to give priority to the more sensitive data ATM has been designed to produce minimal latency and jitter through high speed internal links sending easily manageable units of data called cells cells have a fixed length of 53 bytes 48 bytes for data 5 bytes for the header is widely used for carrying delay sensitive traffic CCNA4 14 Chapter 8 2 WAN Bandwidth Considerations O e Many companies rely on the high speed transfer of data between remote locations Consequently higher bandwidth is crucial because it allows more data to be transmitted in a given time When bandwidth is inadequate competition between various types of traffic ow Band2. and decreases reliability CCNA4 7 Chapter 8 2 WAN Topology Considerations 2 e Many WANs use a Star Topology e As the enterprise grows and new branches are added the branches are connected back to the head office producing traditional star topology Star Topology CCNA4 8 Chapter 8 2 WAN Topology Considerations e When many locations must be joined a hierarchical solution is recommended A mesh network is clearly not feasible because there would be hundreds of thousands of links A three layer hierarchy is often useful when the gt network traffic mirrors the enterprise branch structure and is divided into regions areas and HOAN branches gt CCNA4 9 WAN Topology Considerations e Many enterprise WANs have connections to the Internet e Although the Internet may pose a security problem it does provides an alternative for inter branch traffic Part of the traffic that must be considered 4 during design is going to or li B ia coming from the Internet CCNA4 10 unapter 5 2 WAN Connection I echnologies MEN c gt typical private WAN uses a combination of technologies that are usually chosen based on traffic type and volume Distance capacity up to 45 Mb s E3 T3 Permanent fixed capacity Basic Telephone Distance time 33 56 kb s Dialed slow connection Distance time 64 or 128 k
3. conditions and timing of a WAN link you need to analyze the traffic characteristics specific to each LAN that is connected to the WAN Traffic Characteristics Characteristic Description Connectivity and volume flows Where does this traffic flow and how much traffic flows there Client server data What kind of traffic flows between the client and server Latency tolerance including length and the users tolerate delays variability How much and how often Network availability tolerance How critical is network availability to the users of this LAN Can they tolerate WAN outages or would their work grind to a halt Error rate tolerance Is this noisy traffic Priority Does this traffic have priority over other traffic For example network management messages should have a higher priority than e mail Protocol type What types of protocol operate within the network Average packet length What is the average size of packets being transmitted CCNA4 6 Chapter 8 2 WAN Topology Considerations O E e Designing a WAN topology consists of the following e Selecting an interconnection pattern or layout for the links between the various locations Selecting the technologies for those links to meet the enterprise requirements at an acceptable cost More links increase the cost of the network services but having multiple paths between destinations increases reliability Adding more network devices to the data path increases latency
4. Academy Chapter 8 Network Troubleshooting Part Il CCNA4 1 Chapter 8 2 Network Troubleshooting Review of WAN Communications Router Sages Router CCNA4 2 Chapter 8 2 WAN Communications EE ooa UDO Function at the lower three layers of the OSI model A communications provider normally owns the data links Made available to subscribers for a fee Used to interconnect LANs or connect to remote networks Bandwidth is considerably slower than the LAN The charges are the major cost element Implementation must aim to provide maximum bandwidth at acceptable cost GSU DSU Router Chapter 8 2 Steps in WAN Design End Point Connections 97 LANs Traffic source and destination Review le Availability alternate paths load balancing ee Bandwidth 2 Traffic susceptible to latency and jitter Choose Suitable Technology and Evaluate Installation and operational costs 8 2 Wide variety of traffic types and their varying requirements of bandwidth latency and jitter that WAN links are required to Carry Traffic Types IHNEN NEM Mum Voice Low Low Medium Transaction data for example SNA Medium Medium Medium Messaging e mail High High High File transfer High High High Batch data High High High Network management High High Low Videoconferencing Low Low High CCNA4 5 Chapter 8 2 determine traffic flow
5. Incorrect Control Element Order lt Implicit deny any any Addresses amp Wildcard Masks TCP UDP O Use of established Keyword c 1 Uncommon Protocols mm i 2 Data Link j 1 Physical Useful command The log keyword on ACL entries CCNA4 39 Transport Layer Troubleshooting e Common Network Address Translation NAT Issues nboundand C e Interoperability Issues 2 Incorrect Static NAT MF n Tiere D A transport Timers A 4 Transport 3 Netwo BOOTP DHCP DNS SNMP Tunneling MEM 2 Data Link CCNA4 40 Chapter 8 2 Application Layer Iroubleshooting Application Layer Overview OSI Reference Model TCP IP Reference Model 7 Application TFTP SMTP POP 4 Transport Transport J o CCNA4 41 Chapter 8 2 Application Layer Iroubleshooting O Application Protocols Ports WWW Browser HTP ___ Tep fe _ Electronic Mail Distributed File Service 4 42 Chapter 8 2 e LISSE S UNS PP kN Application Layer Iroubleshooting EE ooo LL A m L Symptoms of Application Layer Problems 54 Symptoms User complaints about slow SS application performance Sener Tere Application error messages Console err
6. ansport 3 Network Power related problems Hardware faults 2 Data Link Cabling faults gt 4 Attenuation i 1 Physical Noise EMI J Interface configuration errors Exceeding design limits CPU Overload CCNA4 21 Chapter 8 2 Physical Layer Troubleshooting e isolating Problems at the Physical Layer Check for bad cables or PELIS works standard has been used Check if devices have been cabled incorrectly Verify proper interface configurations Check operating statistics and data error rates CCNA4 22 Chapter 8 2 D ata SO nooting er Problems 4 Transport ENICTONEN 1 Physical 4 23 CCNA4 24 Symptoms No connectivity at the network layer or above No functionality at the network layer or above Network performance below baseline Excessive Broadcasts Console error messages Chapter 8 2 Problems 1 Physical Chapter 8 2 D Troubleshooting Layer 2 PPP Most problems involve link negotiation R2 show interfaces serial 0 0 0 3 Serial0 0 0 is up line protocol is up Hardware is GT96K Serial ternet address is 10 1 1 2 30 0 bytes BW 128 Kbit DLY 20000 usec 5 txload 1 255 rxload 1 255 pback not set Step 1 Check that the appropriste encapsulation is in use s at it both ends 4 25 Chapter 8 2 Troubleshooting Layer 2 PPP Mos
7. b s up to 2 Dialed slow connection Mb s PRI Volume up to 48 kb s Switched fixed capacity Capacity up to 155 Mb s Permanent variable capacity Capacity up to 45 Mbis Permanent variable capacity Monthly subscription up to 3 Mb s Always on shared Internet Metro Ethernet Monthly subscription up to 500 Mb s Limited geographical scope CCNA4 11 Chapter 8 2 WAN Connection technologies O gt A typical private WAN uses a combination of technologies that are usually chosen based on traffic type and volume Technology Typical Bt Rate Distance capacity up to 45 Mb s E3 T3 Permanent fixed capacity Basic Telephone Distance time 33 56 kb s Dialed slow connection ISDN Distance time 64 or 128 kb s up to 2 Dialed slow connection Mb s PRI Volume up to 48 kb s Switched fixed capacity Capacity up to 155 Mb s Permanent variable capacity Capacity up to 45 Mbis Permanent variable capacity DSL Monthly subscription up to 3 Mb s Always on shared Internet Metro Ethernet Monthly subscription up to 500 Mb s Limited geographical scope CCNA4 12 Chapter 8 2 WAN Connection Technologies e A typical private WAN uses a combination of technologies that are usually chosen based on traffic type and volume Typical Bit Rate Distance capacity up to 45 Mb s E3 T3 Permanent fixed capacity Basic Telephone Distance time 33 56 kb s Dialed slow connection
8. mo PC Chapter 8 2 Network Troubleshooting EE Interpreting Network Diagrams Physical Topology shows the physical layout of the devices connected to the network Device Type Model manufacturer OS Version Cable type and Wiring Closet A Rack 1 identifier Hw eap Ethernet S1 PC1 Cable Spec Cabling Endpoints CCNA4 18 Building B Engineering Building A Main Office T1 R2 SRV2 Leased ISP Facility Frame Relay Cloud WEB Server co4ocated at ISP Rack 1 Shelf 2 Ethernet S2 PC2 Ethernet S3 PC3 Conference Room Sales Office Remote Branch Rm 705 Chapter 8 2 X Network roubleshooting interpreting Network Diagrams gt Logical Topology shows how data is transferred on the network Sey panne Device IDs IP Address and IEEE 41 2 rae _ oil subnet mask G TE Interface IDs oa E DLCI for PVCs VPNs 1oz1ee30 1024 Routing Protocols otatic Routes Data Link protocols and WAN Technologies CCNA4 19 Chapter 8 2 ayer Problems Symptoms Performance lower than baseline Loss of connectivity High collision Network bottlenecks or congestion High CPU utilization rates Console error messages CCNA4 20 Chapter 8 2 Physical Layer Troubleshooting EE e Causes of Physical Layer Problems 7 Application a 6 Presentation 5 Session 4 Tr
9. og messages indicate packet looping Syslog messages that indicate constant address relearning or MAC address flapping messages CCNA4 29 Chapter 8 2 Data Link Layer Troubleshooting e Troubleshooting Layer 2 STP Loops ew Step 2 Discover the topology IMS RA scope of the loop a id The highest priority is to stop g the loop and restore network operation To stop the loop you must know which ports are involved Look at the ports with the highest link utilization packets per second Use the show interface command to display the utilization for each interface and record this information before proceeding to the next step CCNA4 30 Chapter 8 2 172 17 10 21 172 17 20 22 172 17 30 23 Data Link Layer Troubleshooting e Troubleshooting Layer 2 STP Loops Step 3 Break the loop Shut down or disconnect RS the involved ports one at a time eret 72 17 2022 After you disable or disconnect each port check whether the switch backplane utilization is back to a normal level Document your findings ACU PGZ CCNA4 31 Chapter 8 2 Data Link Layer Troubleshooting e Troubleshooting Layer 2 STP Loops ew Step 4 Find and fix the cause of e n the loop ic 2d Investigate the topology Ga g diagram to find Ner c 2 path For every switch on the redundant path Does the switch know the correct STP root s the root port identified correctly e BPDUs received regularly on the ro
10. or messages 5 fi T System loo file messages Siem 7 55 s Dod tonacemen alae A 4 Transport 3 Network 2 Data Link 1 Physical ___ CCNA4 43 Chapter 8 2 Application Layer Problems Verify End to End Layer Protocol Connectivity CCNA4 44 Chapter 8 2 Application Layer Iroublesnooting gt Correc Undo changes not resulting in success Re evaluate plan or seek a second opinion CCNA4 45 In Make NO one I B change at a time J Evaluate and document the results im of the change hapter 8 2
11. ot port and on ports that are supposed to be blocking Are BPDUs sent regularly on non root designated po rts 1 Chapter 8 2 CCNA4 32 Data Link Layer Troubleshooting Ct Troubleshooting Layer 2 STP Loops om E Step Restore the redundancy 2 FUIS X After the device or link that is causing the loop has been found and the problem has been resolved restore the redundant links that were disconnected We have only touched lightly on the subject of troubleshooting STP loops For More Information http cisco com en US tech tk389 tk621 technologies_tech_note09186a0080136673 shiml 5 172 17 10 21 172 17 20 22 CCNA4 33 Chapter 8 2 Network Layer Troubleshooting e Symptoms of Network Layer Problems 7 Application o ML 1 Symptoms Network failure 3 Metwork Network performance below i E baseline 2 Data Link 1 Physical CCNA4 34 Chapter 8 2 Network Layer Troubleshooting oIouuluA A X e Symptoms of Network Layer Problems Network layer problems include any problem that involves a Layer 3 protocol Both routed and routing protocols Network Failure The network is nearly or completely nonfunctional These failures are usually noticed quickly by users and network administrators Yah Think Obviously critical to the productivity of a company CCNA4 35 Chapter 8 2 Network Laye
12. r Troubleshooting cuA e Symptoms of Network Layer Problems Network layer problems include any problem that involves a Layer 3 protocol Both routed and routing protocols Network optimization problems Usually involve a subset of users applications destinations or a particular type of traffic Optimization issues in general can be more difficult to detect and even harder to isolate and diagnose They usually involve multiple layers or the host computer itself Determining that the problem is a Network layer problem can take time CCNA4 36 Chapter 8 2 Network Layer Troubleshooting Check for Network roubleshooting Topology Changes Network Layer Check for Equipment and Connectivity Problems Problems Check Routing Neighbor Relationships Check for Topology Database Issues Check for Routing Table Issues C C N 4 3 7 si in ats i cane ne ins ne ne 202222 222222222222 222 22222222222222 h apte r 8 2 ransport Layer Iroublesnooting O SS Symptoms of Transport Layer Problems We will discuss ACLs and NAT the most commonly implemented Layer 4 security technologies symptoms Intermittent network problems security problems Address translation problems Problems with specific traffic types CCNA4 38 Chapter 8 2 Transport Layer Troubleshooting EE e Common Access Control List ACL Issues Common ACL Issues gt Applied to Incorrect Traffic
13. t PPP problems involve link negotiation f 50 0 0 4 PPP S0 0 0 DSU CSU DSU CSU R2 show interface serial 0 0 0 dem Serial0 0 0 is up line protocol is up Hardware is GT96K Serial Internet address is 10 1 1 2 30 MTU 1500 bytes BW 128 Kbit DLY 20000 usec reliability 255422 mad 1 255 rxload 1 255 Encapsulation PPP tep 2 Confirm that the Link Control Protocol LCP negotiations have succeeded CCNA4 26 Chapter 8 2 EE Troubleshooting Layer 2 PPP Most problems involve link negotiation 50 0 0 50 0 0 DSU CSU 3 DSU CSU Unable to authent 2 2 No name Unable to validate CHAP respon JSERNAME R2 CCNA4 27 Chapter 8 2 DD gt Troubleshooting Layer 2 Frame Relay Can be broken into 4 steps 50 0 1 Frame Relay S0 0 1 Provider CSU DSU CSU DSU Verify that all status LEDs on the 1 Use cable tester to check physical CSU DSU unit are green connection between router and gt a CSU DSU Step 1 Verify the physical connection between the CSU DSU and the router Data Link Layer Troubleshooting O e Troubleshooting Layer 2 STP Loops Step 1 Identify that an STP loop is occurring Symptoms T Loss of connectivity A High CPU utilization on routers High link utilization often 100 percent High switch backplane utilization Hot Standby Router Protocol Duplicate Address Sysl
14. width WAN Link Causes response Bandwidth Available bit transfer rate times to increase i which reduces employee productivity and slows down critical web based business processes High Bandwidth WAN Link CCNA4 15 Chapter 8 2 Gommon WAN Implementation Issues Confidentiality We need to send Our branch depends on I sensitive company the WAN Reliability is Implementation information to our essential Issues branches across the WAN Qos Security End to end Quality of How do we protect Service QoS may be ourselves from security hard to obtain across the threats over the WAN Internet CCNA4 16 Chapter 8 2 N Network Iroubleshooting Network Troubleshooting Wiring Closet A Building A Main Office T1 R2 SRV2 Rack 1 Leased ee Ethernet R2 SVR1 3s T1 R2 R1 Leased Rack 2 WEB TFTP Server Wiring Closet B WEB TFTP Server 192 168 20 254 24 Ethemet R1 S1 Ethemet R1 S2 Rack 4 LIED Rack 1 Building B Shelf 2 Shelf 3 Ethernet S1 PC1 pa Ethernet 192 168 10 0 24 Faoi PeZ Rm 701 Rm 705 Building B Engineering 192 168 10 2 24 192 168 10 10 24 192 168 11 10 24 Admin Admin CCNA4 17 10 1 1 1 30 S0 0 0 192 168 10 1 24 ISP Facility 209 165 200 224 27 209 165 200 225 27 50 1 0 Spip 209 165 200 226 27 10 2 2 1 30 192 168 11 0 24 Fad 192 168 11 1 24 192 168 30 10 24 De
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