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) ? 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 ? 3. Is COMMUNITY a CISCO only or is it part of RFC ? Has any other router vendor implemented this parameter ? 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
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 practice, many providers are configured to not send communities to other providers
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
John W. Stewart II writes:
rfc1997. i think there's a GateD with communities
Yup.
Bay Networks supports them as well, though I'm not sure if it's in the mainstream code...it might only be in 11.01 (ANS code). Dave -- Dave Siegel Sr. Network Engineer (520)388-9000 x130 President dave@rtd.net, dave@page.rtd.com(pager) RTD Systems & Networking, Inc. http://www.rtd.com/~dsiegel/ "Experience the Power of Connectivity"
Walter Towbin wrote:
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) ?
It is propagated further into the Internet. Note that only BGP routers which are configured with specific policies will pay any attention to any communities you set, other than the well-known communities. Unless an ISP decides to set up its policies to handle communities, you can't use communities to influence how it sees your routes.
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 ?
MCI will receive and act on 3561:80
3. Is COMMUNITY a CISCO only or is it part of RFC ? Has any other router vendor implemented this parameter ?
Bay Networks also supports Communities, including the well-known communities: NO_EXPORT (0xFFFFFF01) All routes received carrying a communities attribute containing this value MUST NOT be advertised outside a BGP confederation boundary (a stand-alone autonomous system that is not part of a confederation should be considered a confederation itself). NO_ADVERTISE (0xFFFFFF02) All routes received carrying a communities attribute containing this value MUST NOT be advertised to other BGP peers. NO_EXPORT_SUBCONFED (0xFFFFFF03) All routes received carrying a communities attribute containing this value MUST NOT be advertised to external BGP peers (this
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
-- Paul Knight mailto:pknight@BayNetworks.com IP Engineering, Systems Test Office: (508) 916-7087 Bay Networks, Inc. M/S BL2-02 Lab: (508) 670-8888, x-65404 2 Federal St., Billerica, MA 01821 Fax: (508) 670-4004
Regardless of the COMMUNITY attribute being pushed further or not, one must keep in mind that an AS will only advertise to other AS's the route it has selected itself as "best route". It means that one's ability to influence routing decisions of ASes "far away" is minimal, not to say =zero. Alexandre.
participants (6)
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algold＠lambda.lncc.br -
Dave Siegel -
John Scudder -
John W. Stewart III -
Paul Knight -
Walter Towbin