Community for small IX - problem with 4B ASN

Ondrej Zajicek santiago at
Mon Jan 22 16:16:06 CET 2018

On Mon, Jan 22, 2018 at 02:00:27PM +0100, Piotr Marciniak wrote:
> Dear Advisors ;],
> Thank you for all posts. But still I do not know how to make Bird working
> with 4B communities and if I may do this - whether it will be accepted for
> our peers? In short - I do not know how to adapt to 4B communities following
> examples:
> Is there any way to enable 4B communities in bird.conf?
> I do not have any problem with 4B ASn. I set bgp peering sessions from Bird
> with 4B ASn. Even our IX has AS205082.
> This is why I put 2 questions:
> 1. Is it possible to enable 4B ASn for communities in Bird? Will it work
> with other rouers?
> 2. Can we use instead private ASn just for community filters? Are they
> processed corretly by other Internet routers of our peers?

Well, that depends on exact meaning of 'communities'. There are three
different independent community attributes:

 - 'traditional' communities (RFC 1997)
 - Extended communities (RFC 4360)
 - Large communities (RFC 8092)

Attribute bgp_community is for traditional communities, which are limited
to 16 bit components. So you cannot use 32bit ASNs with them. Also, even
if you used 16bit private ASN as myas, you cannot use them for 32bit

You can use Extended communities (and that is usual setting in IXes),
but they can have one component 32 bit, but not both. So if you have
16bit myas, you could have 32bit peeras.

Or you can use new Large communities, which are fully 32bit, and ditch
both traditional and Extended communities. But this is pretty new
standard and i am not sure how widely is supported by other systems.

Elen sila lumenn' omentielvo

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