[OSPF] I have a question regarding forwarding address

Abhinay R <abhinay.is2006@gmail.com> Wed, 13 July 2016 12:11 UTC

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From: Abhinay R <abhinay.is2006@gmail.com>
Date: Wed, 13 Jul 2016 17:41:05 +0530
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Subject: [OSPF] I have a question regarding forwarding address
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Hi All,
        I have a question on when forwarding address is set in external
LSA?

Suppose I have a route from RIP say 100.1.1.0/24 with nexthop 10.1.1.1 in
routing table and I want to redistribute that route into OSPF, then I feel
below conditions must be vaild to set 10.1.1.1 as forwarding address in the
external LSA that OSPF originates for 100.1.1.0/24 network.

These conditions set the forwarding address field to a non-zero address:

    OSPF is enabled on the ASBR's next hop interface AND

    ASBR's next hop interface is non-passive under OSPF AND

    ASBR's next hop interface is not point-to-point AND

    ASBR's next hop interface is not point-to-multipoint AND

    ASBR's next hop interface address falls under the network range
specified in the router ospf command.

Any other conditions besides these set the forwarding address to 0.0.0.0.


If I have 10.1.1.0/24 network as intra or inter route in OSPF routing table
at the router that imported RIP route, do I originate External LSA with
10.1.1.1 set as forwarding address ?


There is a confusion that if the redistributed network nexthop is present
in routing table as intra inter or connected route, we need to set it as
forwarding address. Please clarify.


While we receive a External LSA with forwarding address set, then we see if
there is a connected, intra or inter route to that nexthop and then use it
to compute the route nexthop. This is clear.

Thanks & Regards,
Abhinay R