Re: BGP4 COMMUNITY attribute
At 02:34 PM 3/27/97 EST, John W. Stewart III wrote:
What is the general concensus about passing communities in the
"community"?
i could see a reason for a subscriber passing communities through a mid-level provider to a top-level provider. but i'm not sure if it makes sense [yet] for top-levels to pass communities between themselves
1. Is COMMUNITY a transitive attribute only between me and my
immediate
upstream supplier or is it being propagated further into Internet (so I can influence how somebody ,say, 5 AS hops away from me sees my routes) ?
the attribute is defined as transitive (i.e., once associated with a route it *stays* associated with the route). however, in
Unless an intermediate provider deliberately changes the value, as opposed to appending to it.
these values aren't an end-to-end thing .. it's simply a way for providers to more easily facilitate routing policies. your comment implies somebody being a bad guy...
Actually, I hadn't necessarily meant to imply "being a bad guy". The comment was meant to show that the "intermediate" ISP has this kind of control over the attribute. In any case, if the decision about whether or not to pass on an attribute (or to modify it) was part of the intermediate ISP's policy, whether or not he/she is a bad guy would depend on varying points of view. Donner
practice, many providers are configured to not send communities to other providers
Is this a conscious decision or just that they have not turned on "send-community"?
both. they don't turn on send-community so that others don't see their communities. maybe they have some whiz-bang features that make configing their neat really cool, and they don't want others to see their communities because it might imply a way for others to do the same thing without the same amount of work
/jws
the attribute is defined as transitive (i.e., once associated with a route it *stays* associated with the route). however, in
Unless an intermediate provider deliberately changes the value, as opposed to appending to it.
these values aren't an end-to-end thing .. it's simply a way for providers to more easily facilitate routing policies. your comment implies somebody being a bad guy...
Actually, I hadn't necessarily meant to imply "being a bad guy". The comment was meant to show that the "intermediate" ISP has this kind of control over the attribute. In any case, if the decision about whether or not to pass on an attribute (or to modify it) was part of the intermediate ISP's policy, whether or not he/she is a bad guy would depend on varying points of view.
to date communities haven't been an end-to-end thing. they have mostly had significance only to adjacent ASs. i do know of a small number of exceptions where a subscriber sets the communities, they're carried through a mid-level provider to a top-level provider, at which point the top-leve. provider reacts in some way (e.g., setting local-pref to a certain value) to me the practical bottom line seems to be that communities are being used to ease the configuration work to achieve certain routing policies, and since an AS has complete autonomy over its routing policies, that AS should have the freedom to keep, add to, or stomp on communities that it hears from others. it's possible that in the future we might have an end-to-end application of communities, but i don't know of one yet, so i'm loathe to mandate anything about how far communities are carried and how much they're kept intact /jws
participants (2)
-
John W. Stewart III -
Paul G. Donner