[c-nsp] Source address on BGP peering set up

[Piltrafilla]

Hi people,

First of all, thank you for all your replies, I'm sorry for the delay
in my answer.

With your feedback I have tried a BGP peering on my home lab between a
Cisco and OpenBSD bgpd:

Cisco
  primary 10.0.0.1
  secondary 192.168.0.1
OpenBSD
 primary 10.0.0.2
 secondary 192.168.0.2

On OpenBSD bgpd configuration I have set up local-address for peer 10.0.0.1:

   neighbor 10.0.0.1
   {
       local-address           10.0.0.2
       remote-as                65500
   }

After configuration on both sides, I did a clear ip bgp 192.168.0.2 on
the Cisco side to force reestablishing the peering as a client
(ephemeral to 179). That's the tcpdump on the OpenBSD side:

10.0.0.1.15357 > 192.168.0.2.179: S 2018010072:2018010072(0) win 16384 
10.0.0.1.15357 > 192.168.0.2.179: S 2018010072:2018010072(0) win 16384

Although Cisco router has a connected secondary IP to peer
192.168.0.2, Cisco tries to set up the peering with the primary
address.

A few seconds later, OpenBSD successfully establishes peering with the
Cisco box as a client (ephemeral to 179) because of the possibility of
configuring local-address:

192.168.0.2.46380 > 192.168.0.1.179: S 957503115:957503115(0) win 65535
192.168.0.1.179 > 192.168.0.2.46380: S 949964186:949964186(0) ack
957503116 win 16384
192.168.0.2.46380 > 192.168.0.1.179: . ack 1 win 65535 
192.168.0.2.46380 > 192.168.0.1.179: P 1:40(39) ack 1 win 65535 : BGP
[|BGP OPEN] (DF) [tos 0xc0]

I know that for many of you, this config could seem in someway really
stupid. That config was thought for a temporary peer migration not for
a definitive config.

Any comments on the results? 

Take Care,

-- Carlos

On Fri, 14 Jan 2005 15:34:32 +0000 (GMT), Stephen J. Wilcox
<steve at telecomplete.co.uk> wrote:
> I thought I'd chip in as everyone else has had a go at this..
> 
> On Fri, 14 Jan 2005, Piltrafilla wrote:
> 
> > Anyone knows how BGP on a Cisco router choose source IP address for peering
> > establishment if no "update-source" command is applied to neighbor? Is it only
> > the primary IP address on the closest interface to neighbor?
> 
> update-source will use the primary address, if no update source is applied it
> will use the ip on the outgoing interface
> 
> > For instance, let's say that you would like to set up a peering using a
> > secondary IP address to between two directly-connected neighbors. Is it
> > setting up loopbacks, static /32 routes and update-source on the neighbors'
> > config the only way to do it?
> 
> no you can just config it like any other ebgp directly connected peer
> 
> > On bgpd of OpenBSD you could set up a "local-address" parameter per
> > neighbor or group that sets up source IP address used for that
> > peering. I haven't found any similar parameter on cisco bgp neighbors'
> > config.
> 
> it doesnt have it
> 
> Steve
> 
>