Troubleshooting Redistribution Problems in OSPF

This section describes problems related to redistribution in OSPF. When a router in OSPF does the redistribution, it becomes an ASBR. The routes that are redistributed into OSPF could be directly connected routes, static routes, or dynamically learned routes from another routing protocol or another OSPF process.

The following are problems that can happen during redistribution:

• ASBR is not advertising redistributed routes.

• OSPF is not installing external routes in the routing table.

The second problem already was discussed in the earlier section on OSPF routes installation problems. The first problem is discussed in the section that follows.

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Whenever a route is known to be connected or static, or when any other routing protocol is redistributed into OSPF, an external LSA is generated for that route. If an OSPF router is not advertising the external route even after the redistribution, this indicates a problem on a router that is doing the redistribution. Mostly, the problem stems from configuration mistakes.

The most common causes of this problem are as follows:

• The subnets keyword is missing from the ASBR configuration.

• distribute-list out is blocking the routes.

Figure 9-80 shows a network experiencing this problem. In this figure, R1 is running RIP on Ethernet and redistributing RIP routes into OSPF.

Figure 9-80. Network Setup Shows Redistribution in OSPF

Figure 9-80. Network Setup Shows Redistribution in OSPF

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