System information

Troubleshooting TCP/IP 7-119
RIP/IGRP: Routes Missing from Routing Table
Host and Router Subnet Mask Mismatch Example
In classful IP networks, every router and host in the same major network should share a common
subnet mask. If there are disagreements on the length of the subnet mask, packets are not routed
correctly.
Table 7-10 shows how a UNIX host and a router will interpret an IP address differently if they have
different subnet masks specified for the same major network.
Routes are not being
redistributed properly
between autonomous
systems or between
routing protocols
This problem is restricted to environments in which route redistribution is being
performed between autonomous systems or between multiple routing protocols.
Step 1 Use the show running-config privileged exec command on routers that
border multiple networks running different routing protocols.
Step 2 Examine the router global configuration command entries for the
enabled routing protocols.
Step 3 If the router is running IGRP only, check whether the autonomous system
designated for all connected networks is the same.
Routes are not automatically redistributed between different autonomous
systems. If the router igrp commands indicate different autonomous
systems, route redistribution must be manually configured using the
redistribute router configuration command.
For example, to redistribute routes between IGRP autonomous system 71
(network 15.0.0.0) and IGRP autonomous system 109 (network
192.31.7.0), enter the following commands:
C7010(config)#router igrp 71
C7010(config-router)#redistribute igrp 109
C7010(config-router)#distribute-list 3 out igrp 109
C7010(config-router)#access-list 3 permit 192.31.7.0
C7010(config)#router igrp 109
C7010(config-router)#redistribute igrp 71
C7010(config-router)#distribute-list 5 out igrp 71
C7010(config-router)#access-list 5 permit 15.0.0.0
Step 4
If the router is running multiple routing protocols, look for a redistribute
router configuration command entry. Make sure that routing information
is being properly exchanged between protocols.
For example, to redistribute routes between RIP (running in network
15.0.0.0) and IGRP autonomous system 109 (network 128.1.0.0), enter
the following commands:
C7010(config)#router igrp 109
C7010(config-router)#network 128.1.0.0
C7010(config-router)#redistribute rip
C7010(config-router)#default-metric 10000 100 255 1
1500
C7010(config-router)#distribute-list 10 out rip
C7010(config-router)#access-list 10 permit 15.0.0.0
Routes are not being
redistributed properly
between autonomous
systems or between
routing protocols
Step 5 If you want static routes to be redistributed between autonomous systems
or between two different routing protocols, use the redistribute static
router configuration command.
For example, to redistribute static routes in IGRP autonomous systems,
add the following command to the configuration:
C7010(config-router)#redistribute static
For more information on using the redistribute router configuration command, see
the Cisco IOS configuration guides and command references.
Possible Problem Solution