When the forwarding address is set to 0.0.0.0, then the exit point for this
destination is the ASBR which originated the LSA. Then look up the RT, for
an entry to reach the ASBR. If the forwarding address is non-zero, then the
exit point for this destination is different from the one that originated
the LSA. In this case you need to look up your RT for an entry to reach the
forwarding address.

consider,

        asbr----|
        | |------fwd
        |
        |
      DUT

when asbr imports an external route into your AS, it can set the next_hop
(forwarding address) to either itself or a third party gateway (a
forwarder). So depending upon what forwarder address being set in the LSA
and the type of the external LSA, DUT can calculate the cost to reach
external network and select the least one.

Thanks
Ilan

> -----Original Message-----
> From: Mailing List [mailto:OSPFDISCUSS.MICROSOFT.COM]On Behalf Of
> Umesh_MS
> Sent: Friday, July 20, 2001 2:15 PM
> To: OSPFDISCUSS.MICROSOFT.COM
> Subject: [OSPF] Doubt aboutType 5 route calculation
>
>
>
>
>
> Hi,
> In section 16.4 of ASExternal route calculation in RFC 2328,I am not
> very clear with what to be done when forwarding address is zero and when
> it is non-zero.
> Should we only compare routes when the forwarding address is non zero or
> must be done for even when the forwarding address is zero.
> Point 3 and 4 are they related with forwarding address in this section.
>
> Thanx in advance
> Umesh
>

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