Subject: [Idr] Clarification for section 9.1.2 of rfc4271

From: "Ilya Varlashkin" <[email-masked]>
Date: Tue, 23 Oct 2007 12:46:02 +0200

Hi,

in the section 9.1.2 of RFC4271 third paragraph has phrase:

"..., or if it would become unresolvable if the route was installed in
the routing table, the BGP route MUST be excluded from the Phase 2
decision function."

Consider a BGP router (say, router C) that received prefix 192.2.1.1/32
from two different iBGP neighbours as follow:

1) neighbour A set NEXT_HOP to itself and local-pref for this prefix is
100; this update was received first (in time)
2) neighbour B preserved original next-hop, which happened to be
192.2.1.1 and local-pref for this prefix is 150 (this update was
received later)

There are no any other routing information (whether via BGP or any other
protocol) known to router C.

Router C at the moment has 192.2.1.1/32 prefix in it's RIB pointing to
router A's address. In this condition, does update from router B falls
under cited requirement "would become unresolvable" and should it be
excluded from further consideration or is it permissible (per RFC) to
select such update as best and install it to the RIB?

Kind regards,
iLya

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From: Tony Li <[email-masked]>
Date: Tue, 23 Oct 2007 08:18:02 -0700

> Consider a BGP router (say, router C) that received prefix  

Yes, that would result in recursive resolution and as such would not  
be resolvable.

Tony