Re: bgp router with multi asn's - neighbor config ?

4 Sep 2014

      On 2.9.2014 23:36, Kai wrote:
...
G'day!
Hi!
...
For the configuration we want to set up, I couldn't find any details in
the docs, the wiki or the list archive. So please allow me to ask my
questions here (questions see below).
desired setup:
We want to establish a router ('A') announcing two different ASNs
(as1,as2) to it's neighbours. In fact we want to setup three routers A,
B and C, all of them corporately announcing as1 and as2.
You cannot have two BGP relations to a single peer. I see two options:

1) You will announce two different AS paths with the same first AS:

 < as1 >
 < as2 as1 >

so you can see as2 is announced "behind" as1.

2) You can announce two same as paths:

 < as1 >
 < as2 >

But the peer must disable check on 1st AS in AS paths. Cisco command
"no bgp enforce-first-as"

In both case the configuration is:
 protocol bgp {
   local as <as1>;
   neighbor X as as9;
   (...)
 }

Different is synthesis of propagated prefixes.

		Ondrej
...
I'd guess the config on router A should include some lines like these:
 protocol bgp {
   local as <as1>;
   neighbor X as as9;
   (...)
 }
 protocol bgp {
   local as <as2>;
   neighbor X as as9;
   (...)
 }
X being one of the neighbours and announcing as9.
Question 1: Is this basically the correct approach?
Question 2: What would be the correct config on router X (A's neighbour)
in this setup? Would it look like:
 protocol bgp {
   local as <as9>;
   neighbor A as as1;
   (...)
 }
 protocol bgp {
   local as <as9>;
   neighbor A as as2;
   (...)
 }
Question 3: Does anyone have a pointer to a text/tutorial/whatever that
explains in detail what config is needed for this kind of setup?
Best regards, Kai

Re: bgp router with multi asn's - neighbor config ?

Ondrej Filip