Question about OSPF LSA 5 and 7
Hi guys! one short question.. just a little doubt that's spinning in my head:
Why LSA 5 does not follow LSA 7 rules regarding the Forwarding Address? I mean, in LSA 7, there's always an IP Address in the Forwarding Address field, and it's the highest IP among the OSPF enabled loopbacks, and if none, highest OSPF enabled Interface.
But, LSA 5 gets an Forwarding Address of 0.0.0.0 if the External route resolves to a non-OSPF interface, so then it needs an LSA 4 so ABRs can show the world how to get to this route. How come it cant get a Forward address just like a LSA 7 (and translated LSA5)?
What am I missing :S?
Comments
With a single NSSA translator for 7-to-5 you are most likely to need
additional "hint" for optimal routing toward the original ASBR. Type-5
LSAs in contrary are originated by ASBR itself, and FA "hint" may only be
needed in a few certain cases to help selecting optimal path. In general,
routing toward ASBR for external routes is optimal and safest path.
HTH,
Petr
----- Original Message -----
From: "omarmontes"
Sent: Fri, September 11, 2009 9:27
Subject:[CCIE R&S] Question about OSPF LSA 5 and 7
Hi guys! one short question.. just a little doubt that's spinning in my head:
Why LSA 5 does not follow LSA 7 rules regarding the Forwarding Address? I
mean, in
LSA 7, there's always an IP Address in the Forwarding Address field, and
it's the
highest IP among the OSPF enabled loopbacks, and if none, highest OSPF
enabled
Interface.
But, LSA 5 gets an Forwarding Address of 0.0.0.0 if the External route
resolves to a
non-OSPF interface, so then it needs an LSA 4 so ABRs can show the world
how to get
to this route. How come it cant get a Forward address just like a LSA 7 (and
translated LSA5)?
What am I missing :S?
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