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E2 routes flapping in ABR ?


Hi ,

   I have an ABR which receives routes from an ASBR as E2 routes.When I check the routes in the routing table of ABR, I find only the E2 routes flapping frequently.Can anyone let me know the reason for the same?


Giuseppe Larosa
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Hello Muthupriyanka,

you haven't provided enough information.

you should collect information about the OSPF activity on both the ABR and the ASBR nodes.

also be aware that you should check the OSPF database in order to see if the routes are actually flapping or not.

you can use

show ip ospf database external

on both ABR and ASBR nodes

In your network there might be competition between routes injected in the OSPF domain by two different ASBR nodes, or somewhere the routes are redistributed from OSPF into another protocol and then back in OSPF may be as O E1 routes.

But to say something meaningful we should see the OSPF database entries.

Check also reachability of the ASBR node itself as the routes may be not used if the ASBR node is considered not known.

you can use

show ip ospf border-routers

on the ABR node to check this

or you can look for LSA type 4 in the OSPF database

is the ASBR located in one of the areas to which the ABR is directly connected or in a remote area?

in first case ABR checks bits in ASBR node router LSA in second case it checks the OSPF LSA type 4 for the ASBR router-id

Hope to help


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