Re: [Idr] [Technical Errata Reported] RFC4271 (5001)

<> Wed, 19 April 2017 18:45 UTC

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To: "Alvaro Retana (aretana)" <>, "John G. Scudder" <>
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Thread-Topic: [Technical Errata Reported] RFC4271 (5001)
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Date: Wed, 19 Apr 2017 18:45:34 +0000
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Subject: Re: [Idr] [Technical Errata Reported] RFC4271 (5001)
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Alvaro, John, all

I may have one comment. Please see inline. 

> From Alvaro Retana (aretana)  > Sent: Wednesday, April 19, 2017 8:01 PM
 > [Cut the distribution.]
 > idr WG:
 > I think this report is a lot clearer than the other one John filed (#5000), so I am going to
 > mark this one as “Hold for Document Update” [1].
 > Just because this report is related to the use of “MAY NOT” I will wait until we resolve the
 > other one just in case.
 > Thanks!
 > Alvaro.
 > [1]
 > On 4/19/17, 1:40 PM, "RFC Errata System" <> wrote:
 > The following errata report has been submitted for RFC4271,
 > "A Border Gateway Protocol 4 (BGP-4)".
 > --------------------------------------
 > You may review the report below and at:
 > --------------------------------------
 > Type: Technical
 > Reported by: John Scudder <>
 > Section: 5
 > Original Text
 > -------------
 >    BGP implementations MUST recognize all well-known attributes.  Some
 >    of these attributes are mandatory and MUST be included in every
 >    UPDATE message that contains NLRI.  Others are discretionary and MAY
 >    or MAY NOT be sent in a particular UPDATE message.
 > Corrected Text
 > --------------
 >    BGP implementations MUST recognize all well-known attributes.  Some
 >    of these attributes are mandatory and MUST be included in every
 >    UPDATE message that contains NLRI.  Others are discretionary and
 >    sending them in a particular UPDATE message is OPTIONAL.

IMHO, OPTIONAL may not be what was intended.
As per RFC 2119 " the adjective "OPTIONAL", mean that an item is
   truly optional.  One vendor may choose to include the item because a
   particular marketplace requires it or because the vendor feels that
   it enhances the product while another vendor may omit the same item."
Here, I think that the original intention was to say that the attribute MAY be sent if appropriate and MAY be omitted if appropriate. IOW, it is _not_ REQUIRED to always send it.

As an example, quickly parsing RFC 4171, it does not seem to indicate whether the LOCAL_PREF attribute is mandatory or discretionary. But given that it is well-known, as per §5, it can only be mandatory or discretionary. Given that it usually does not appear in EBGP session, I would argue that it is not mandatory, hence discretionary. But I don't think that we could say that sending the attribute LOCAL_PREF is OPTIONAL given that RFC 4271 mandates its use in IBGP (plus not sending it on some IBGP sessions would create forwarding loops).

I may propose the follow text: Others are discretionary and may or may not be sent in a particular UPDATE message
Or: Others are discretionary and are not required to be sent in all UPDATE message


 > Notes
 > -----
 > The original text uses "MAY NOT" capitalized as if it were an RFC 2119 keyword. However,
 > RFC 2119 does not have any defined meaning for "MAY NOT". In context, it is unlikely the
 > reader would be at risk of misinterpreting the text, but nonetheless it's a misuse of RFC
 > 2119 terminology and difficult to parse if reading closely.
 > (The replacement text was suggested by Eric Rosen; thanks.)
 > Instructions:
 > -------------
 > This erratum is currently posted as "Reported". If necessary, please
 > use "Reply All" to discuss whether it should be verified or
 > rejected. When a decision is reached, the verifying party
 > can log in to change the status and edit the report, if necessary.
 > --------------------------------------
 > RFC4271 (draft-ietf-idr-bgp4-26)
 > --------------------------------------
 > Title               : A Border Gateway Protocol 4 (BGP-4)
 > Publication Date    : January 2006
 > Author(s)           : Y. Rekhter, Ed., T. Li, Ed., S. Hares, Ed.
 > Category            : DRAFT STANDARD
 > Source              : Inter-Domain Routing
 > Area                : Routing
 > Stream              : IETF
 > Verifying Party     : IESG
 > _______________________________________________
 > Idr mailing list


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