Most vendors do not allow multiple local AS numbers, I think. The fact you receive the route over iBGP tells nothing about its origin, because external routes are passed over iBGP as well. Could you imagine a straightforward universal algorithm for guessing that the route is originated by your iBGP AS number?
On Wed, Oct 9, 2024 at 4:13 PM Ochalski, Radoslaw <rocha...@akamai.com> wrote: > We receive this route via IBGP on IBPG session and then exporting it to > EBGP, I am pretty sure most vendor implementations will automatically > prepend IBGP ASN. Otherwise, we are missing one ASN in ASPATH and > attracting more traffic. > > Yes, I am aware we can prepend it, though it seems strange this is not > default behavior. > > > > *Kind Regards,* > > > > Radek > > > > > > *From: *Alexander Zubkov <gr...@qrator.net> > *Date: *Wednesday, October 9, 2024 at 3:30 PM > *To: *"Ochalski, Radoslaw" <rocha...@akamai.com> > *Cc: *Ondrej Zajicek <santi...@crfreenet.org>, Bird-users < > bird-users@network.cz> > *Subject: *Re: BIRD is not prepending ASN on EBGP export. > > > > Hi Radoslaw, In your case, how should BIRD know in what ASN the routes are > originating? The AS number appears when you do export via eBGP session. And > it uses local ASN for that. If you need your routes to pretend to be > originated in AS20940, > > ZjQcmQRYFpfptBannerStart > > *This Message Is From an External Sender * > > This message came from outside your organization. > > ZjQcmQRYFpfptBannerEnd > > Hi Radoslaw, > > > > In your case, how should BIRD know in what ASN the routes are originating? > The AS number appears when you do export via eBGP session. And it uses > local ASN for that. If you need your routes to pretend to be originated in > AS20940, you need to prepend AS20940 in some filter to your routes. > > > > On Wed, Oct 9, 2024 at 11:09 AM Ochalski, Radoslaw <rocha...@akamai.com> > wrote: > > 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" <santi...@crfreenet.org <mailto: > santi...@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: santi...@crfreenet.org <mailto: > santi...@crfreenet.org>) > "To err is human -- to blame it on a computer is even more so." > > >
