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Chapter 6

Troubleshooting TCP/IP Connectivity

Router_C>

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,

* - candidate

default U - per-user static route, o - ODR

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 2 subnets

C 172.16.50.0 is directly connected, Ethernet0/0

C 172.16.60.0 is directly connected, Ethernet0/1

Router_C>

As suspected, Router C does not know a route to Router A, and it has no

gateway of last resort. This explains why the ICMP request was not sent
back to Router A.

These examples show how useful the ping and traceroute commands

are when troubleshooting TCP/IP router and network problems. Be sure to
use them in conjunction for the best results.

show Commands

The show commands provide router- and interface-specific information. Sev-
eral show commands were discussed in previous chapters. Due to the number
of show commands available on the router, they must be discussed within the
context they are used.

Each troubleshooting session requires the use of different show com-

mands. The common show commands used to troubleshoot TCP/IP com-
mands are listed as follows:

show ip interface

This command provides information specific to

the TCP/IP configuration of the specified interface. Information regarding

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