System information

Troubleshooting TCP/IP 7-117
RIP/IGRP: Routes Missing from Routing Table
Misconfigured route filtering Step 3 If distribute-list commands are configured on the router, disable them
using the no version of the command.
For example, to disable an incoming filter that references access list 10,
enter the following command:
C7500(config)#no distribute-list 10 in
Step 4
After disabling all distribution lists on the router, use the clear ip route
privileged exec command to clear the routing table.
Step 5 Determine whether the routes appear in the routing table by using the
show ip route privileged exec command.
Step 6 If routes appear properly in the routing table, the access list referenced by
the distribute-list command is probably configured to deny certain
updates.
Step 7 To isolate the problem list, enable distribution lists until routes stop
appearing in the routing table. (You might have to use the clear ip route
command after enabling each list.)
Step 8 Use the show running-config command and make sure that the problem
list does not deny updates inappropriately. If the access list denies updates
from specific addresses, make sure that it does not deny the address of a
router from which routing updates should be received.
Change the access list to allow the router to receive updates from the
proper addresses. At the end of every access list is an implied “deny all
traffic” criteria statement. Therefore, if a packet does not match any of
your criteria statements, the packet will be blocked. Configure explicit
permit statements for those addresses from which the router should
receive updates.
Step 9 If you altered an access list, enable the distribution list using the
distribute-list command. Use the clear ip route command and check
whether the missing routing information appears in the routing table.
Misconfigured route filtering In the following example, the Enhanced IGRP routing process accepts
only two networks—network 0.0.0.0 and network 131.108.0.0:
access-list 1 permit 0.0.0.0
access-list 1 permit 131.108.0.0
access-list 1 deny 0.0.0.0 255.255.255.255
router eigrp
network 131.108.0.0
distribute-list 1 in
Step 10
If the routes appear, perform the preceding steps on all routers in the path
until the routing information appears properly, with all distribution lists
enabled.
For more information on configuring access lists, see the Cisco IOS configuration
guides and command references.
Possible Problem Solution