BIRD is not prepending ASN on EBGP export.

[Ochalski, Radoslaw]

Thanks Ondrej,

So for the routes originating in AS20940, downstream will not be aware of AS20940 in the as-path it will only know private AS4290006033.

Kind Regards, 

Radek 


On 10/8/24, 5:18 PM, "Ondrej Zajicek" <santiago at crfreenet.org <mailto:santiago at crfreenet.org>> wrote:


!-------------------------------------------------------------------|
This Message Is From an External Sender
This message came from outside your organization.
|-------------------------------------------------------------------!


On Tue, Oct 08, 2024 at 04:46:07PM +0200, Alexander Zubkov via Bird-users wrote:
> Hi Radoslaw,
> 
> Do I get it right, that you have 2 bgp peerings here. First your route
> passes this peering:
> AS8075 <-> AS20940
> then it passes other peering:
> AS4290006033 <-> AS4290006002
> 
> Then it is an expected behaviour. Because the ASN is prepended when
> route is exported over eBGP session. And the local ASN is prepended.
> So you see that when you receive the route over the first peering, it
> is prepended with AS8075. Then it goes over the second peering, where
> it is prepended with AS4290006033.


Yes, that is true. I would add that one is not supposed to have different
local ASNs for different BGP instances that form coherent BGP router,
unless it is configured as BGP confederation or manually patched by
filters.


-- 
Elen sila lumenn' omentielvo


Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org <mailto:santiago at crfreenet.org>)
"To err is human -- to blame it on a computer is even more so."