Re: [Idr] Question about BGP Large Communities

"Sriram, Kotikalapudi (Fed)" <> Wed, 05 February 2020 01:28 UTC

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From: "Sriram, Kotikalapudi (Fed)" <>
To: John Heasly <>, "Jakob Heitz (jheitz)" <>
CC: "" <>, "" <>
Thread-Topic: Question about BGP Large Communities
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Date: Wed, 05 Feb 2020 01:28:41 +0000
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Subject: Re: [Idr] Question about BGP Large Communities
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> > Does anyone want to co-author and suggest changes?
I would also be glad to participate in that effort.

I have looked at the proposals in the two drafts (Jacob and John H).  
There are a few observations I would like to share.

As Alvaro pointed out, RFC 8092 says:
   This document defines the BGP Large Communities attribute as an
   optional transitive path attribute of variable length.

That means *all* BGP Large Communities are transitive. Do you agree?
RFC 8195 seems to be written in that spirit as well. 

The first 32 bits together are a Global Administrator (GA) ID.
So, it seems it would not be possible to use any part of it as data.
Otherwise, collisions (ambiguity) could happen when 
other LCs use 4-octet ASNs in the Global Administrator field. Agree?
I see Jacob's draft proposes using some portion of the first 32 bits as data.
The draft that John Heasly shared sets the first 32-bits to ASN value 0
to designate WK-LC;  so no part of the first 32-bits is data.

Another idea to consider: 
Why not request IANA to assign a range of 256 or 1024 or some number (?) 
of 4-byte ASN values to be allocated and used as GA ID for transitive WK-LCs?
A function (e.g., route-leak protection) that requires transitive WK-LC 
will be allocated one these ASN values.
Then we don't waste any part of the first 32-bits to designate "type" of LC.
That cleanly leaves 64 bits for local data (as RFC 8092 specifies)
which can accommodate two 4-byte ASNs if needed.


> -----Original Message-----
> From: John Heasly <>
> Sent: Tuesday, February 4, 2020 5:55 PM
> To: Jakob Heitz (jheitz) <>
> Cc: Sriram, Kotikalapudi (Fed) <>; Job Snijders
> <>; Nick Hilliard <>; John Heasly
> <>;;;;
>;; Brian Dickson
> <>
> Subject: Re: Question about BGP Large Communities
> Tue, Feb 04, 2020 at 08:45:40PM +0000, Jakob Heitz (jheitz):
> > A set of well known large communities could be useful.
> > I have a draft that I never submitted attached to this email.
> > Does anyone want to co-author and suggest changes?
> Hey Jacob,
> I'd work on that with you.  Job, Morrow and I also started a draft for
> Large WKCs, but we have not submitted anything - nor made any recent
> progress.
> IIRC, the direction we were intending to use 0 (zero) as the ASN, then
> define local data part 1 as WKC itself, and local data part 2 to be a
> value associated.
> I've attached that I have written so far.  Job and Morrow may or may not
> endorse this approach at this point.
> -heas