Upstream BGP community support

Richard A Steenbergen ras at
Fri Nov 6 20:34:45 UTC 2009

On Fri, Nov 06, 2009 at 04:50:10PM +0100, Daniel Roesen wrote:
> On Thu, Nov 05, 2009 at 11:06:56PM -0600, Richard A Steenbergen wrote:
> > Definitely a problem. The point of using 65123:45678 in the first place
> > (with a private ASN field in the "AS part") is to avoid stepping on
> > anyone else's ASN with your internal use community.
> Actually, as far as I have seen yet, it's more like being able to
> derrive/describe community from ASN-to-act-on, e.g.
> 61234 meaning "prepend 3 times"
> 45678 meaning "this is the neighbor AS I want this to be applied to"

No I'm not saying otherwise. My point was that the reason it is
"65123:45678" instead of "45678:65123" is that they're using a value
from the private ASN range for the "action" tag, thus eliminating the
potential for collisions with anyone else's real ASNs. As you pointed
out, the ASN and Data fields are no longer going to be the same bit
size, so the "flipping the fields" trick will no longer work. The only
solution will be to add a non-transitive target type and do

Richard A Steenbergen <ras at>
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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