Re: [Idr] I-D Action: draft-ietf-idr-large-community-04.txt

"Jakob Heitz (jheitz)" <jheitz@cisco.com> Tue, 25 October 2016 19:48 UTC

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From: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
To: David Freedman <david.freedman@uk.clara.net>, "idr@ietf.org" <idr@ietf.org>, Jeff Haas <jhaas@juniper.net>
Thread-Topic: [Idr] I-D Action: draft-ietf-idr-large-community-04.txt
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Date: Tue, 25 Oct 2016 19:47:57 +0000
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Subject: Re: [Idr] I-D Action: draft-ietf-idr-large-community-04.txt
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We added that as a result of Jeff Haas's email attached.

It actually makes sense.
However, if we want to keep parity with https://tools.ietf.org/html/rfc7606#section-7.8
it's no big deal for me.

Jeff?

Thanks,
Jakob.


> -----Original Message-----
> From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of David Freedman
> Sent: Tuesday, October 25, 2016 9:54 AM
> To: idr@ietf.org
> Subject: Re: [Idr] I-D Action: draft-ietf-idr-large-community-04.txt
> 
> Apologies for the ultra-late-last-minute input, but I was discussing this with Job offlist and we felt it should be
> seen by list participants.
> 
> My point was about RFC1997 parity and the length validation.
> 
>  " A Large BGP Communities attribute with a length of zero MUST be ignored upon receipt and removed when sending."
> 
> Later wording here has been discussed to be amended (I understand) to:
> 
> " A Large BGP Communities attribute with a length of zero MUST NOT be sent and MUST be ignored upon receipt."
> 
> Well, I wanted to point out, that RFC1997 was of course updated by RFC7606.
> 
> In (7606), the following two comments are made:
> 
> " For all path attributes other than those specified as having an attribute length that may be zero, it SHALL be
> considered a syntax error for the attribute to have a length of zero."
> 
> And
> 
> " The error handling of [RFC1997] is revised as follows: The Community attribute SHALL be considered malformed if
> its length is not a non-zero multiple of 4"
> 
> So really, if you apply RFC7606 to RFC1997 you have lost parity if you accept a zero length community (even if you
> just ignore it).
> 
> My suggestion here is just to drop the passive receive tolerance of the zero length largecomm, since it seems out of
> place (even if it is harmless).
> and let it be considered malformed and handled by RFC7606.
> 
> Thoughts?
> 
> Dave.
> 
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--- Begin Message ---
   On Sep 21, 2016, at 4:31 PM, Randy Bush <randy@psg.com<mailto:randy@psg.com>> wrote:



            The attribute consists of a set of Large Communities.



         a bgp update may contain a large community attribute which is composed
         of zero or more large communities.  or one or more if you insist.



      ack.



   zero or one?


   1 or more.

   Implementations may prune empty path attributes (and probably should) when the contents are lists.  However, I don't believe we should standardize sending 0 of these communities as a form of signaling.

   That said, in the error handling section, it should note that a length of zero shall not be treated as a malformed route.

   -- Jeff

--- End Message ---