From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Sun May 11 2003 - 15:07:31 GMT-3
The BGP path selection process does not use admin distance as a criteria. If
you have two paths, go through the path selection process and see where one
is selected over the other. With IGP to BGP redistributeion, item# 4 can
cause problems.
Before anything -- if a route is not synchronized it is thrown out!!
1) Next Hop address/network given for the reaching the network is available
in the IP routing
2) The route with the highest Weight attribute is chosen (the Weight
attribute is Cisco proprietary)
3) The route with the highest Local_Preference attribute is chosen
4) Any routes that were learned Locally (next-hop = 0.0.0.0) have a
preference
5) The route with the shortest AS_Path attribute is chosen. (confed learned
paths are not included.)
6) The route with the lowest Origin is chosen [internal (0), external (1),
incomplete (2)]
7) The route with the lowest Multi-Exit Discriminator (MED) is chosen
8) The route learned via EBGP is chosen (iBGP routes are discarded at this
point)
9) The route with the nearest IGP neighbor is chosen
10) The oldest learned route is preferred.
11) The route with the lowest BGP router-id is chosen
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Richard Davidson
Sent: Friday, May 09, 2003 4:30 PM
To: groupstudy
Subject: confederation path selection and Admin distance?
confederation path selection and Admin distance?
I have a confederation issue. I can't figure out why
my router is selecting the iBGP confederation peer as
apposed to my eBGP peer.
My router has to paths. I think, before the path
selection algorithm the router looks at admin
distance. Well the route that is being injected has a
distance of 200 and the route that is not has a
distance of 20. I brought down the link to the iBGP
confederation peer and the eBGP neighbor with a
distance of 20 came up.
See attached:
router bgp 65001
no synchronization
bgp log-neighbor-changes
bgp confederation identifier 100
bgp confederation peers 65000
neighbor 172.16.101.1 remote-as 65001
neighbor 172.16.101.1 update-source Loopback0
neighbor 172.16.103.1 remote-as 65000
neighbor 172.16.103.1 ebgp-multihop 255
neighbor 172.16.103.1 update-source Loopback0
neighbor 172.30.4.10 remote-as 1771
r4#sib 140.10.1.0
BGP routing table entry for 140.10.1.0/24, version 99
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to non peer-group peers:
172.16.101.1 172.30.4.10
(65000) 1581 1776
172.40.10.10 (metric 200) from 172.16.103.1 (172.16.103.1)
Origin IGP, localpref 100, valid, confed-external, best
1771 1581 1776
172.30.4.10 from 172.30.4.10 (192.88.1.1)
Origin IGP, localpref 100, valid, external
r4#i | i 140.10.1.0
B 140.10.1.0 [200/0] via 172.40.10.10, 00:27:50
This archive was generated by hypermail 2.1.4 : Mon Jun 02 2003 - 15:13:40 GMT-3