IBGP cannot import prefixs with its as_path

[Ondrej Zajicek]

On Mon, Sep 20, 2021 at 11:18:04PM +0800, 智慧雨泽 wrote:
> Hi,
>          I use ibgp to transport full tables in my network. iBGP delete my
> ASN but I use my ASN to identify my prefixes.
>         So I added this code to my ibgp import filter
> if bgp_path ~ [= =] then {
> #bgp_path.prepend(LOCAL_ASN);
> if my_opt_prefix() then bgp_path.prepend(LOCAL_ASN);
> }
> It works when 2 servers connect, but when I have 3 servers, the third
> server can not import my first server's prefixed with my ASN.
> ...
> I know that maybe no one will use ibgp like this, but why it won't work?


Hi

That is expected behavior. IBGP does not attach local ASN number
to AS path in order to have consistent route selection in AS.

Also, if you attach your ASN manually, you trigger loop-prevention
in the next receiver and received routes are ignored.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."