Troubleshooting Tools - the Netgroup at Politecnico di Torino
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1.2. ping Output Example PING www xenia it 209 238 252 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 64 bytes from 209 238 252 252 252 252 252 252 252 252 252 252 133 133 133 133 133 133 133 133 133 133 133 56 data bytes icmp_seq 0 tt1 113 fime 1318 icmp_seq 1 tt1 113 time 1738 icmp_seq 2 tt1 113 time 1756 icmp_seq 3 ttl 11 icmp_seq 4 ttl 11 icmp_seq 5 ttl 11 icmp_seq 6 tt1 113 icmp_seq 7 ttl 113 icmp_seq 8 ttl icmp_seq 9 tt1 113 www xenia it PING Statistics gt 10 packets transmitted 10 pai round trip ms min ay S received 0 packet loss x 902 1562 1808 ms Round trip time RTT time elapsed from the transmission of an ICMP Echo Request to the reception of the corresponding ICMP Echo Reply it is a measure of the distance between local and target host troubleshooting_tools odp 5 ping Working Principle Testing host sends an ICMP Echo Request message to target host Target host replies with ICMP Echo Reply message 0 Echo Request 8 Echo Reply troubleshooting_tools odp 6 Interpreting ping Outcome Data Identifier Sequence Number If replies are received connectivity to target host exists When replie
3. 130 192 3 17 Gateway 130 192 3 17 127 0 0 1 130 192 28 127 0 0 130 192 28 130 192 28 130 192 28 0 0 0 0 0 0 255 255 0 0 255 Interface 130 192 28 127 0 0 130 192 28 127 0 0 130 192 130 192 130 192 Persistent Routes None troubleshooting_tools odp 16 netstat Output Example T continue IPv4 Statistics Packets Received 1762191 Received Header Errors 12 Received Address Errors 655093 Datagrams Forwarded ICMPv4 Statistics Received Messages 1246 Errors Destination Unreachable 371 Time Exceeded Parameter Problems Source Quenches Unknown Protocols Received Received Packets Discarded Received Packets Delivered 1127699 Output Requests 951452 Routing Discards o Discarded Output Packets Output Packet No Route Reassembly Required Reassembly Successful Reassembly Failures Datagrams Successfully Fragmented Datagrams Failing Fragmentation Fragments Created Redirects Echos Echo Replies Timestamps Timestamp Replies Address Masks Address Mask Replies TCP Statistics for IPv4 Active Opens Passive Opens Failed Connection Attempts Reset Connections Current Connections Segments Received TE 167 a iat 7 L neers 4 1003 L L REE A HH Segments Sent Segments Retransmitted troubleshooting_tools odp 17 l R U ZL IS netstat Output Exa
4. 9 0 0 GW1 DFW1 ALTER NET 146 188 240 45 47 886 ms 47 380 ms 50 690 ms iad w3 gw customer ALTER NET 137 39 138 74 69 827 ms 68 112 ms 66 859 ms library airnews net 206 66 12 202 174 853 ms 16 945 ms 147 501 ms 8 721 ms 6 123 ms 15 400 ms 49 921 ms 16 476 ms 7 011 ms 6 684 ms 47 371 ms Round trip time RTT time elapsed from the transmission of an ICMP Echo Request to the reception of the corresponding ICMP Time Exceedded message it provides a very loose measure of the travel time between local host and each router Sometimes travel time changes significantly in the course of a few seconds due to temporary congestion of routers troubleshooting_tools odp 10 Traceroute Working Principle 1 Local host sends an ICMP Echo Request message in IP packet with TTL 1 2 First router default gateway decrements TTL and discards IP packet and reacts sending ICMP TTL Exceeded in Transit 3 Local host receives ICMP TTL Exceeded in Transit and from source address of encapsulating IP packet learns one IP address of first router gt Specific interface depends on router implementation gt Might be interface through which IP packet was sent 4 Local host sends another ICMP Echo Request message in IP packet with incremented TTL TTL 2 5 Default gateway forwards IP packet decrementing TTL 1 6 Second router on the path decrements TTL and discards IP packet and reacts sending ICMP TTL Exceeded in Transi
5. mple Interface Statistics Received Sent Bytes 458905257 313090297 Unicast packets 786574 805622 Non unicast packets 1565173 34366 Discards 0 Errors 0 Unknown protocols 232253 troubleshooting_tools odp 18 LEERE PE t a route Displays and modifies IP routing table m Syntax B route options command parameters Option Description Displays routing table equivalent to netstat r add NetAddr mask Adds route for network NetAddr NetMask e g NetMask Gateway 10 0 0 0 255 255 255 0 through next hop Gateway delete NetAddr Removes route for network NetAddr NetMask e g mask NetMask 10 0 0 0 255 255 255 0 through next hop Gateway Gateway troubleshooting_tools odp 19 TETEPI CEEE EEL ipconfig parameters Syntax ipconfig options Displays and modifies some of the IP stack oo E no param Displays main TCP IP configuration data addresses netmask default gateway DNS server all Displays all TCP IP configuration data addresses netmask default gateway DNS server lease time for DHCP assigned addresses displaydns Displays local host DNS cache Flushes local host DNS cache troubleshooting_tools odp 20 troubleshooting_tools odp 21 troubleshooting_tools odp 22 ipconfig Output Example C gt ipconfig Windows IP Configuration Ethernet adapter Local Area Con
6. nection Connection specific DNS Suffix IP Address Subnet Mask IP Address IP Address IP Address fe80 20b dbff fe14 50bb 8 Default Gateway 130 192 16 17 e80 207 ebf fe7e c60 8 130 192 16 81 255 255 255 0 ipconfig Output Example Windows IP Configuration truciolo Primary Dns Suffix Node Type Hybrid IP Routing Enabled No WINS Proxy Enabled Ethernet adapter Local Area Connection Connection specific DNS Suffix Description Physical Address 00 0B DB 14 50 BB Dhcp Enabled No IP Address Subnet Mask IP Address IP Address IP Address fe80 20b dbff fe14 50bb 8 Default Gateway 130 192 16 17 fe80 207 ebff fe7e c60 8 130 192 3 21 130 192 3 24 fec0 0 0 ffff 1 1 130 192 16 81 255 255 255 0 DNS Servers fec0 0 0 ffff 3 1 2001 760 400 1 3c71 db18 e713 fd56 2001 760 400 1 20b dbff fe14 50bb 3Com 3C920 Fast Ethernet 3C905C TX 2001 760 400 1 3c71 db18 e713 456 2001 760 400 1 20b dbff fe14 50bb ipconfig Output Example C gt ipconfig displaydns Windows IP Configuration www polito it Record Name www polito it Record Type 5 Time To Live 86398 Data Length 4 Section CNAME Record web01 polito it localhost Record Name Record Type Time To Live Data Length Section Answer L a L L A Host Record 127 0 0 1 a L L a troubleshooting_tools odp 23 BUBUBUE
7. ng_tools odp 13 TETEE netstat 4 L L L L k Syntax a Shows main network parameters netstat options no param Lists active layer 4 connections and sessions a Lists active layer 4 connections and sessions as well as TCP or UDP servers on the loacl host s Shows per protocol layer 3 and 4 statistics S C troubleshooting_tools odp 14 T E E E Rh Active Connections Local Address http epmap https 2747 2747 2748 Proto TCP TCP TCP TCP truciolo truciolo truciolo truciolo truciolo truciolo truciolo truciolo isakmp 1030 1078 2040 2359 3456 4500 ntp truciolo truciolo truciolo truciolo truciolo truciolo truciolo troubleshooting_tools odp 15 microsoft ds netstat Output Example Foreign Address truciolo 0 truciolo 0 truciol truciolo localhost 2748 localhost 2747 netstat Output Example State LISTENING LISTENING LISTENING LISTENING ESTABLISHED ESTABLISHED 00 10 4b 35 MS TCP Loopback interface 3Com EtherLink PCI Active Routes Network Destination 0 0 0 0 127 0 0 0 130 192 0 0 130 192 28 4 130 192 255 255 224 0 0 0 255 255 255 255 Default Gateway 0 0 255 0 255 255 255 255 255 255 224 0 255 Netmask 255 255 255 255
8. s are not received Arouting problem might exist on the path from local host to target A routing problem might exist on path from target to local host The two paths might not be the same Routers might be configured not to forward IP packets containing ICMP messages A firewall on the path might filter out ICMP messages A Personal Firewall on the local host or target host might filter out ICMP messages troubleshooting_tools odp 7 troubleshooting_tools odp 8 Traceroute Shows the likely path or route to the target host Shows routers traversed by packets traveling from local host to target host IP address or domain name of one interface of each router is shown Not necessary the interface having received or forwarded the packet Syntax traceroute options target UNIX tracert options target Windows traceroute to library airnews net 206 66 12 202 30 hops max 1 e JW K wn troubleshooting_tools odp 9 Traceroute Output Example Byte pa rbrt3 208 225 64 50 4 867 ms 4 893 ms 3 449 ms 519 Hssi2 0 0 GW1 EWR1 ALTER NET 157 130 0 17 6 418 ms 113 ATM3 0 XR2 EWR1 ALTER NET 146 188 176 38 6 323 ms 192 ATM2 0 TR2 EWR1 ALTER NET 146 188 176 82 6 955 ms 105 ATM6 0 TR2 DFW4 ALTER NET 146 188 136 245 49 105 ms 298 ATM7 0 XR2 DFW4 ALTER NET 146 188 240 77 48 162 ms 48 052 ms 47 565 ms 194 ATM
9. t Some Unix implementations send a UDP message rathern than an ICMP Echo Request message Traceroute Options Description TTL used as initial value for Time To Live field in first IP packet rather than the default 1 Uses ICMP Echo Request messages rather than UDP messaged UNIX only Generates UDP messages to port destination port rather than default 33434 UNIX only Uses count as the maximum value for the Time To Live field rather than the default 30 L timeout Areply is waited for at most timeout milliseconds if a later reply is ignored a count test messages are generated for each value of the Time To a Live field default is three a a a troubleshooting_tools odp 11 E E E h REE LEU ETE LL a a m arp S Shows and modifies ARP cache content a Syntax z arp options IPAddr EthAddr Options Description a Shows the current ARP cache content highlighting static and dynamic entries a d IPAddr Eliminates from ARP cache MAC address mapping L corresponding to host IPAddr s IPAddr EthAddr Adds stating mapping between network address IPAddr L and data link address EthAddr L a a troubleshooting_tools odp 12 BOSBUBUESE Interface 130 192 16 81 0x30004 Internet Address Physical Address 130 192 16 17 00 e0 63 13 7e 01 130 192 16 36 00 10 4b 35 f 2 fa a u L a L L troubleshooti
10. troubleshooting_tools odp 3 Troubleshooting Tools An overview of the main tools for verifying network operation from a host Fulvio Risso Mario Baldi Politecnico di Torino Technical University of Turin see page 2 B 98 49 J 9 Notes The commands programs described in this presentation are commonly available both on UNIX and Windows workstations Nevertheless Options and parameters might be different Output might be different Hence Content of this presentation should not be taken literally It should be used as a starting point Command syntax and output should be double checked Moreover only options and parameters considered relevant to our purposes are listed here For some commands an equivalent program with graphic interface might exist ping Checks network reachability of a host Syntax Ping options target ICMP Echo Request messages sent continually until Ctrl C is pressed in UNIX this is default behaviour Sends count ICMP Echo Request messages in Windows default count is 4 Live field containing TTL only Windows ICMP Echo Request messages are sent into IP packet with Time To troubleshooting_tools odp 4 timeout A reply is waited for at most timeout milliseconds if a later reply is ignored Possibly records path taken by packets by activating Record Route option in the ICMP Echo Request message
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