From: Alexei Monastyrnyi (alexeim@orcsoftware.com)
Date: Tue Nov 14 2006 - 12:32:11 ART
Hi Group!
I remember reading that BGP advertises only the best route out.
I came across a scenario where one RR talks to two clients peering the
same remote AS and getting the same route sets from outside. Simple
enough - like a multi-homing with one ISP.
RR (R5) learns both sets of routes from the clients and advertises one
best set, so that one RR client R6 has a redundant path in its BGP table
but another one (R1) doesn't. I understand that as soon as that R1
looses its EBGP connectivity, it will get routes from RR. But at that
stable point BGP routing tables no R1 and R6 are different.
RR has multipath enabled.
R5#sh ip bgp 199.172.4.0
BGP routing table entry for 199.172.4.0/24, version 50
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Multipath: eBGP iBGP
Advertised to peer-groups:
RRC
254, (Received from a RR-client)
150.100.5.254 (metric 100) from 5.5.1.1 (5.5.1.1)
Origin IGP, metric 0, localpref 100, valid, internal, multipath, best
254, (Received from a RR-client)
150.102.5.254 (metric 100) from 5.5.6.6 (5.5.6.6)
Origin IGP, metric 0, localpref 100, valid, internal, multipath
Is is possible to advertise a valid non-best route? I came to conclusion
that it is not, but I might miss some fine point.
TIA,
A.
This archive was generated by hypermail 2.1.4 : Fri Dec 01 2006 - 08:05:46 ART