Re: Seeming contradiction on forwarding addresses?

[Acee Lindem <[e-mail]>]

Hi Mike,

Mike Fox wrote:

>RFC 2328 says, in section 12.4.4.1 regarding forwarding addresses in
>external LSAs:
>
>
>
>>Note that when the forwarding address field is non-
>>zero, it should point to a router belonging to
>>another Autonomous System.
>>
>>
>
>But then when discussing calculation of external routes in section  16.4 it
>says:
>
>
>
>>If the forwarding address is non-zero, look up the
>>forwarding address in the routing table.[24] The matching
>>routing table entry must specify an intra-area or inter-area
>>path; if no such path exists, do nothing with the LSA and
>>consider the next in the list.
>>
>>
>
>So the RFC says that a forwarding address should be to an AS external
>address, but no one can use an external LSA if the only way to reach the
>forwarding address is via an AS External route?  Footnote 24 re-emphasizes
>that point also.  Is there something I am missing here?
>
The  thing here is that the forwarding address is for a router that
provides a path to IPv4 prefixes
outside the OSPF routing domain. However, the forwarding address itself
must be reachable
by an OSPF intra-area or inter-area route (which is by definition part
of the OSPF routing
domain).  In this context, I prefer to use the term OSPF routing domain
rather than AS since
there will often be non-OSPF routes in use within an AS running OSPF as
the IGP.

I hope I've made sense.

Acee



>
>Mike
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