System information

Troubleshooting TCP/IP 7-105
TCP/IP: Local Host Cannot Access Remote Host
Routing is not enabled on
one or more routers
Step 1 Use the trace exec command to isolate the problem router (or routers).
Syntax:
trace [protocol] [destination]
Syntax Description:
• protocol—(Optional) Protocols that can be used are AppleTalk,
CLNS
2
, IP, and VINES.
• destination —(Optional) Destination address or host name on the
command line. The default parameters for the appropriate protocol are
assumed and the tracing action begins.
The following are the characters that can appear in trace output:
• nn/msec—For each node, the round-trip time in milliseconds for the
specified number of probes.
• *—The probe timed out
• ?—Unknown packet type
• Q—Source quench
• P—Protocol unreachable
• N—Network unreachable
• U—Port unreachable
• H—Host unreachable
Step 2 When you find a suspect router, determine whether routing is enabled on
the router. Enter the show ip route privileged exec command to view the
routing table. Examine the output to see whether the routing table is
populated with routing information.
Step 3 If routing information is not being exchanged (that is, if the output of the
show ip route command shows no entries that were learned from a
routing protocol), use the show running-config privileged exec
command on the router.
Routing is not enabled on
one or more routers
Step 4 Look for a router global configuration command for the routing protocol
that should be enabled.
For example, if the router should be running IGRP, look for an entry such
as the following:
router igrp 109
network 192.168.52.0
network 192.168.48.0
Step 5
If routing is not enabled on the router (or routers), enable the proper
routing protocol using the router global configuration command.
Step 6 In router configuration mode, enter the appropriate network commands
to associate networks with the routing process, as applicable.
For example, to enable IGRP routing for networks 193.166.66.0 and
193.168.25.0, enter the following configuration commands:
Router(config)# router igrp 109
Router(config-router)# network 193.166.66.0
Router(config-router)# network 193.168.25.0
For complete information on configuring specific IP routing protocols, see the
Cisco IOS Network Protocols Configuration Guide, Part 1 and Network Protocols
Command Reference, Part 1.
Possible Problem Solution