From: ccie19226 (ccie19226@googlemail.com)
Date: Sun Feb 24 2008 - 17:12:49 ARST
From what I can tell...
Before you issue the update-source command - the neighbor relationship will
come up as the two routers are on the same subnet (1.1.1.0/x) - thus the
ebgp-multihop configuration is redundant. This is a stock standard eBGP
configuration.
Once you add in the update-source command you then have the following
situation:
R1 is configured to open a BGP session using its lo0 interface (11.11.11.11)
however R2 is configured to expect it from 1.1.1.1.
In reverse R2 is configured to open a BGP session using it's lo0 interface
(12.12.12.12) however R1 is configured to expect it from 1.1.1.2.
If you fix up the neighbor statements on each side to reflect the lo0
addresses and not the directly connected interfaces - issuing the
update-source command should see your neighbor relationships work all the
time assuming the underlying IGP is working correctly. In this case you need
to ebgp-multihop configuration to manipulate the ttl of the BGP messages to
allow you more that 1 hop (the default).
** side note - your config below has R2 pointing to itself for the
ebgp-multihop as opposed to R1 which is the correct neighbor to configure.
Hope that makes some sense. Gl with it!
Con.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Matt
Bentley
Sent: Saturday, 23 February 2008 15:55
To: Cisco certification
Subject: BGP Update-Source Question
I thought I had a really good understanding of this, but it seems I am
wrong.
I have a BGP neighbor relationship between two devices
R1 (1.1.1.1) -------------> R2 (1.1.1.2)
R1 Fa0/1 connects to R2 Fa0/1
Underlying protocol for BGP transport is EIGRP
R1 Config:
router bgp 1
bgp router-id 1.1.1.1
neighbor 1.1.1.2 remote-as 2
neighbor 1.1.1.2 update-source l0
neighbor 1.1.1.2 ebgp-multihop
!
int l0
ip add 11.11.11.11 255.255.255.0
R2:
router bgp 2
bgp router-id 2.2.2.2
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 update-source l0
neighbor 1.1.1.2 ebgp-multihop
!
ip add 12.12.12.12 255.255.255.0
!
I can ping both the IP addresses as well as the loopback addresses. If I
bring the neighbor relationship up first, and then issue the update-source
option, it doesn't kill the neighbor relatinoship, however, if I bounce the
interfaces, it gives the following debug. What am I missing?
*Mar 1 00:03:43.819: BGP: 1.1.1.1 open active, local address 12.12.12.12
*Mar 1 00:03:43.819: BGP: 1.1.1.1 read request no-op
*Mar 1 00:03:43.819: BGP: 1.1.1.1 open failed: Connection refused by remote
host, open active delayed 14770ms (35000ms max, 60% jitter)
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