Best practices for BGP Communities

Wed Mar 6 01:16:02 UTC 2019

On Wed, Mar 6, 2019 at 8:32 Smith, Courtney <Courtney_Smith at comcast.com>
wrote:

> On 3/5/19, 6:04 PM, "NANOG on behalf of Job Snijders"
> <nanog-bounces+courtney_smith=comcast.com at nanog.org on behalf of
> job at instituut.net> wrote:
>
>     On Sun, Mar 03, 2019 at 08:42:02PM -0500, Joshua Miller wrote:
>     > A while back I read somewhere that transit providers shouldn't delete
>     > communities unless the communities have a specific impact to their
>     > network, but my google-fu is failing me and I can't find any sources.
>     >
>     > Is this still the case? Does anyone have a source for the practice of
>     > leaving unknown communities alone or deleting them?
>
>     https://tools.ietf.org/html/rfc7454#section-11
>
>
> Remember policies between two peers may not be same as customer policies.
>
> Example:  Customers_of_transit_X >>> Transit X >>> Peer_A >>
> Customers_of_Peer_A
>
> Customers_of_Peer_A may use community A:50 to set local pref to 50 in
> Peer_A network.  But that doesn’t not mean Customers_of_transit_X can send
> A:50 to set lpref on their routes in Peer_A's network.  Peer_A's policy
> with Transit X likely does not take action on customer communities since
> they are 'peers' not customers.  Transit X can send A:50 to Peer_A but
> nothing would happen.  What's the benefit of Transit X preserving A:50 from
> its customers if it means nothing in Transit X?

OP didn’t specify what kind of BGP communities they were referring to. In
general we can separate communities into two categories: “Informational”
and “Action”. You are right that preserving/propagating “action”
communities (such as in your example) probably isn’t that interesting.
“informational” communities on the other hand can be very valuable.

See https://tools.ietf.org/html/rfc8195 for more information on how the two
types differ.

Kind regards,

Job
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