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Krishna_251070's avatar
Krishna_251070
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Aug 07, 2018

OSPF stuck in Exstart

Hello,

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
10.10.26.9        1   ExStart/Backup  00:00:37    172.16.207.2    /Inbound
10.10.26.10       1   ExStart/DROther 00:00:34    172.16.207.3    /Inbound
LTM-01[2]>

From debug in Cisco Router:

863027: Aug  7 11:37:12.920 PDT: OSPF-26 ADJ   Gi0/1: Send DBD to 172.16.207.254 seq 0x238E opt 0x52 flag 0x7 len 32
863028: Aug  7 11:37:12.920 PDT: OSPF-26 ADJ   Gi0/1: Retransmitting DBD to 172.16.207.254 [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!

  • This issue was caused by ACL blocking unicast traffic between OSPF peers. The multicast address 224.0.0.5 was permitted in the ACL. That is reason why the adjacency state moved till EXSTART.

     

    DBD packet exchange happens using the unicast addresses.