From: gscisco@xs4all.nl Cisco (gscisco@xs4all.nl)
Date: Sun Apr 23 2006 - 18:00:03 GMT-3
Hi,
I hope you guys can help me understand this as IBGP and EBGP routes behave
different than I have always understood them.
From what I read in cisco's "BGP Best Path Selection Algorithm" -
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.
shtml#background
7 - Prefer eBGP over iBGP paths.
However it is not the behavior I'm seeing myself
I have the following setup
CE1 === default route -> / <- static redistributed in BGP === PE 1
CE2 ====== running BGP ====================================== PE 2
PE1 and PE2 are within the same AS and run iBGP between them.
I have a network 157.161.77.0/24 which PE1 has a static route for which it
redistributes into BGP. PE2 gets this same network
from CE2 via (e)BGP. It however does not take this as the best BGP path as
keeps prefering the internally learned one via iBGP
PE3#sh ip b 157.161.77.0
BGP routing table entry for 157.161.77.0/24, version 5
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
161.239.99.2
Local
172.16.1.3 (metric 11) from 172.16.1.3 (213.239.99.3)
Origin incomplete, metric 10, localpref 100, valid, internal, best
<<<<< iBGP learned path
65000
161.239.99.2 from 161.239.99.2 (161.239.99.2)
Origin IGP, localpref 100, valid, external <<<<<<<<<< eBGP learned
path
Am I misinterpreting cisco's path algorithm ? Furthermore I also see that it
should have taken the the latter path as it's Origin is better as well
(IGP goes before "incomplete") ?
Can anyone shine a light on this for me as I'm quite confused.
Thanks in advance,
Vincent
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