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Krishna_251070's avatar
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Aug 07, 2018

OSPF stuck in Exstart


I am facing an issue with enabling OSPF between a Cisco Router and F5 LTM. The OSPF adjacency process is getting stuck at exstart phase.

This is how my toplogy looks like:

Cisco Router<-------Cisco L2 Switch------->F5 LTM

LTM-01[2]>show ip os neighbor

OSPF process 26:
Neighbor ID     Pri   State           Dead Time   Address         Interface        1   ExStart/Backup  00:00:37    /Inbound       1   ExStart/DROther 00:00:34    /Inbound

From debug in Cisco Router:

863027: Aug  7 11:37:12.920 PDT: OSPF-26 ADJ   Gi0/1: Send DBD to seq 0x238E opt 0x52 flag 0x7 len 32
863028: Aug  7 11:37:12.920 PDT: OSPF-26 ADJ   Gi0/1: Retransmitting DBD to [8]

Here I can see that the router is actively sending DBD packets to F5, but no reply back.

All the device are running interface MTU of 1500 bytes. I am not sure how to debug OSPF in F5 device.

Any help would be appreciated!

3 Replies

  • This issue was caused by ACL blocking unicast traffic between OSPF peers. The multicast address was permitted in the ACL. That is reason why the adjacency state moved till EXSTART.


    DBD packet exchange happens using the unicast addresses.