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Troubleshooting TCP/IP 7-127
IP Enhanced IGRP: Routers Not Establishing Neighbors
Figure 7-13 An OSPF Virtual Link Example
IP Enhanced IGRP: Routers Not Establishing Neighbors
Symptom: Enhanced IGRP routers are not establishing neighbor relationships properly. Routing
information is not distributed to routers.
Table 7-13 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 7-13 IP Enhanced IGRP: Routers Not Establishing Neighbors
Virtual link is
misconfigured
Step 1 Check the configuration of the routers at each end of the virtual link using
the show running-config privileged exec command.
Look for area area-id virtual-link router-id router configuration
command entries. These commands are used to configure the virtual link.
Step 2 Use the show ip ospf exec command to find the router ID (IP address) of
the routers.
Step 3 Add the area area-id virtual-link router-id command if it is missing, or
modify it if it is incorrect. Make sure that the proper area ID and router ID
(IP address) are specified. The routers at each end of the virtual link must
point to one another across the transit area.
For example, in the network shown in Figure 7-13, a virtual link from
Router B to Router A is created across the transit area, Area 1.
The following commands are entered on Router A:
C4500(config)#router ospf 250
C4500(config-router)#network 121.10.0.0 0.0.255.255
area 0
C4500(config-router)#network 169.192.56.0 0.0.0.255
area 0
C4500(config-router)#area 1 virtual-link 121.10.100.46
On Router B, the following commands are used:
C4000(config)#router ospf 250
C4000(config-router)#network 121.10.0.0 0.0.255.255
area 0
C4000(config-router)#network 108.31.0.0 0.0.255.255
area 2
C4000(config-router)#area 1 virtual-link 121.10.1.1
1 LSA = link state advertisement
2 ASBR = autonomous system border router
Possible Problem Solution
Interface E0
121.10.1.1
Interface E1
169.192.56.10
Interface E1
108.31.1.1
Interface E0
121.10.100.46
Area 2
Area 1
(transit area)
Area 0
(backbone)
Router BRouter A