Re: [Idr] RFC 4360 clarification (BGP Extended CommunitiesAttribute)

["Dhananjaya Rao (dhrao)" <dhrao at cisco.com>]

>-----Original Message-----
>From: idr-bounces at ietf.org [mailto:idr-bounces at ietf.org] On 
>Behalf Of Pradosh Mohapatra (pmohapat)
>Sent: Monday, August 03, 2009 1:53 PM
>To: bruno.decraene at orange-ftgroup.com; idr at ietf.org
>Subject: Re: [Idr] RFC 4360 clarification (BGP Extended 
>CommunitiesAttribute)
>
>Hi Bruno,
>
>
>| We have a clarification question regarding RFC 4360. Section "6.
>| Operations" states that "If a route has a non-transitivity extended
>| community, then before advertising the route across the Autonomous
>| System boundary the community SHOULD be removed from the route."
>| 
>| Is it compliant with the specification to:
>| -a- set / add, on the outbound policy of an eBGP session, a non
>| transitive extended community?
>| -b- expect that the eBGP peer will not remove it to enforce the
>| non-transitivity?
>| 
>| It seems to us that this is compliant:
>| -a- seems to be inlined with the operation of well know communities
>| defined in RFC 1997 where the advertisement restrictions applies when
>| BGP receive a route with this community, not when it advertise it.
>| -b- RFC 4360 does not ask the eBGP to enforce the non-transitivity
>(and
>| besides, non-transivity is a SHOULD, not a MUST)
>| 
>| - Could you please correct or confirm this?
>| - If your BGP implementation removes a non-transitive community
>| received
>| over an eBGP session, could you please tell us? (either privately or
>on
>| the mailing list).
>
>
>The implementations I know of will strip out the 
>non-transitive extcomms
>even if they get attached through the outbound policy before 
>advertising
>them to EBGP peers. And yes, it would also remove all non-transitive
>extcomms received over an EBGP session.
>

Although this does seem to be different from the behavior for other
non-transitive attributes, for example MED. Any good reason for it to
be different ? Seems like this behavior would in fact prevent a
non-transitive extended community from being used between 2 ASes.

Thanks,
-Dhananjaya

>- Pradosh
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