From: George Spahl (g.spahl@xxxxxxxxxxxxx)
Date: Fri May 17 2002 - 21:32:35 GMT-3
Greetings,
It seems that if a route enters an AS with the community attribute
attached (set to "no-export" for example), then the EBGP peer that
receives the route will not advertise this route to any other EBGP peer.
However, he is not obliged to send the community attribute to his IBGP
peers along with the route. Instead the "neighbor send community" must
be configured for any IBGP peer of his that needs to see the community
attribute. Is that correct so far?
If so, then whenever I send a route to an AS with "no-export" set,
expecting that my route won't be advertised beyond that AS, I'm very
much relying on the assumption that the peers within the receiving AS
have been configured to send the community attributes on to their
internal peers, especially those which have EBGP connections to other
ASs. This way those peers would know that my route should not be
advertised to any other AS. Otherwise, I suppose, the first peer upon
receiving the route would send the route along to his IBGP peers without
the "no-export" attached and they would think it's OK to advertise to
other ASs. Is this also correct?
If this is actually how it works then is it common practice on the
Internet to configure the BGP peers within a transit AS so that the
community attributes are forwarded on to each other? Corrections,
clarifications, comments anyone?
Thanks,
George
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