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
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