looking for some help with bgp extended communities

[Ondrej Zajicek]

On Tue, Dec 01, 2015 at 02:53:05PM -0800, Warren Turkal wrote:
> Hi networkers,
> 
> I'd like to use bgp extended communities instead of communities for my
> routing policy so that I can use the 4-octet ASN. However, I am a bit
> confused by the route target vs route origin (and not having other kinds).
> Would it be appropriate to use the route origin (as opposed to the route
> target) kind of ECs to hold the community data that I will use for routing
> policies? Or maybe is there a way to use the generic 0x04 sub type instead
> of ro and rt kinds?

Hi

Unfortunately, BGP extended communities are unncecessary complex. But you
can use any community in any way you want as long as you are using your
4-octet ASN. Currently, route-target and route-origin are just labels
with no internal meaning in BIRD. Generic extended community based on
draft-ietf-idr-as4octet-extcomm-generic-subtype is not yet implemented in
syntax, but you can probably use 'unknown 4' for that or use 'generic'
keyword for any ext. comm. with some low-level hacking. These are not explicitly
documented, but are used in filter test config:

https://gitlab.labs.nic.cz/labs/bird/blob/master/filter/test.conf

Unfortunately, authors of ext.comm. specification do not foresee that
with 4-octet ASNs and typed communities people would need both 4-octet
global part and 4-octet local part, therefore (with type header) 10
octets instead of 8 octets per ext.comm. And they did not include
equivalent of basic community in the main ext.comm. specification.


> Also, is it legitimate to use some private ASN for global communities that
> can be set by any of my routers when talking to one another?

Probably yes as long as you filter out them on AS borders.

-- 
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."
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