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Tuesday, December 8, 2009

OSPF not working on new link


Currently we have ospf running on our network between R1,R2+R3(linear - See diag), ospf is configured on each router to use loop address(/32) as it's router-id. We introduced a link between R1+R3, and ospf is not working - we see R1 + R3 sending hellos via the new link, but not receiving any reply over this new link(ping connectivity is working fine) - our guess is that the routes for the loop addresses that ospf is using as router-id, are currently learnt via ospf via R2, and this is causing ospf on the new link to fail? We have confirmed that ospf is definitely enabled on the new interfaces, and have disabled passive interface on them.

Debugging options
  1. If you issue 'show ip ospf interface', you should see the network OSPF type - if it set to NON-BROADCAST, you must configure a neighbor statement under the OSPF process or change the OSPF network to 'broadcast' or 'point-to-point'.
  2. If you have MD5 enabled, try disabling MD5 and see if the OSPF comes up, if it does make sure the same MD5 password is entered on both devices.
  3. MTU mismatch can affect adjacencies.
  4. You can try the 'ip opsf mtu-ignore' command or make sure the MTU matches on the neighbors.
  5. Both of your routers may think they are the DR and your are using a /30 address as IP address for both side. Confirm and check if anything is blocking the OSPF multicast address. You can try to change it to unicast. int xxxx ; ip ospf network non-broadcast ; router ospf xx ; neighbor x.x.x.x
  6. Try by setting priority in one interface. This will make one Router as DR , another with lowest priority as BDR. interface XXXX ; ip ospf priority X (range value 0-255)
  7. Try to configure both the interface as OSPF Point to Point. interface XXXX ; ip ospf network point-to-point
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