Re: BGP4 COMMUNITY attribute
Actually, along this vein (granted, this may not be the place but since the subject came up).. What is the general concensus about passing communities in the "community"? See in-line below... At 01:32 PM 3/27/97 EST, John W. Stewart III wrote:
many of your questions are for MCI and not nanog
In the preparation for upcoming 2nd (multihomed) connection to Internet I am looking into COMMUNITY attribute of BGP4 as a way (in conjunction with my own LOCAL_PREF) of load balancing traffic between my two internet links (both T3). After reading CISCO documentation I am still not clear on some issues:
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.
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"? Donner
2. If COMMUNITY propagates into big I, and I set COMMUNITY to 3561:70 (for MCI to set LOCAL_PREF on my routes to 70) and my next hop supplier sets COMMUNITY of my routes to 3561:80, what happens ? what MCI is going to do ?
is one of your immediate upstream provider's MCI? if so, then you would tag routes with 3561:70 and MCI would immediately see and react to that. however, you imply that your "next hop supplier" isn't MCI, which makes it a bit odd for you to be sending communities for MCI, but is doable if your "next hop supplier" agrees to carry your communities all the way to MCI
3. Is COMMUNITY a CISCO only or is it part of RFC ? Has any other router vendor implemented this parameter ?
rfc1997. i think there's a GateD with communities
/jws
4. Which major Internet providers have COMMUNITY/LOCAL_PREF implemented (I am aware of MCI and Sprint) ?
5. Your experiences, comments, suggestions .....
Thanks in advance, Walter
Walter Towbin Telus Advanced Communications phone: 403-543-2032, fax: 403-543-2030, cell: 403-620-0019 walter.towbin@telus.com
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...
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
participants (3)
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John W. Stewart III -
Paul G. Donner -
randy＠psg.com