Tuesday, March 16, 2010

Non Zero Forwarding Address In LSA 5

Forwarding Address is used in OSPF to avoid extra hop count when traffic is routed to an external ASBR. The value of forwarding address in LSA 5 can either be zero or non zero. The forwarding address sets to when the ASBR redistributes the external routes and OSPF is not enabled on next hop interface. The forwarding address sets to non zero when any of the following condition occurs:-
1.OSPF is enabled on the ASBR’s next hop interface.
2.ASBRs next hop interface is not point to point and point to multipoint.
3.ASBRs next hop interface falls under the network range specified in the router OSPF.

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ippoint said...

Nice info. Would like to know what would be the forwarding address in case of non-zero. I believe it should be the next-hop local interface IP address if that interface is included in network statement.

shivlu jain said...

you are right.