Does Bird supports AS_Trans 23456

[Ondrej Zajicek]

On Tue, Aug 28, 2018 at 11:48:31AM +0000, gerta toli wrote:
> HI Ondrej,
> 
> 
> This is my configuration
> 
> protocol bgp eBGP4byteASN {
> debug all;
>    import all;
>    export filter out;
>    local as "my-4byteASN";
>    neighbor 192.168.0.1 as 65535;
>    source address 192.168.0.2;
> }
> 
> 
> So my peer 192.168.0.1 understands only 2byte ASN , but I have 4byte
> ASN. ASN_Trans is used in case of such scenario by the 4byte ASN routers.
> So  supposedly, Bird should send open message using the ASN 23456, since
> it knows that it is peering with an old 2byteASN router. The error im
> showing is below:

That is how it works: OPEN message itself contains always 2byte ASN or
ASN 23456 in the main ASN field and 4B ASN is stored in optional field,
so it is ignored by the peer that does not understand the optional field.

If the peer reports Bad peer AS: my_4byteASN, then the peer most likely
understands 4byte ASNs, because it can read the optional field.
Therefore, it should be configured with your 4B ASN as peer ASN.

The fact that the peer itself uses 2B ASN is irrelevant. The important
distinction is whether the peer understands 4B ASN capability, which
likely is supported by most BGP software/firmware that is not older
than ~10 years.

-- 
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."