Re: [Idr] [Technical Errata Reported] RFC4271 (5000)

"Alvaro Retana (aretana)" <aretana@cisco.com> Wed, 19 April 2017 17:56 UTC

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From: "Alvaro Retana (aretana)" <aretana@cisco.com>
To: "idr@ietf.org" <idr@ietf.org>
Thread-Topic: [Technical Errata Reported] RFC4271 (5000)
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Date: Wed, 19 Apr 2017 17:56:12 +0000
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Subject: Re: [Idr] [Technical Errata Reported] RFC4271 (5000)
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[Cutting the distribution a little.]

[John: thanks for filing this report.]

idr WG:

As you know, changes to rfc4271 should be handled with care.  And this case is no exception.

Even if “MAY NOT” is not an rfc2119 keyword as “MAY”, “MUST NOT”, and others are, it doesn’t give me a great feeling to change it for one that is – among other things because the meaning of “MAY” and “MUST” is so different.  Of course, making me feel good is not the purpose of rfc2119… ;-)

Having said that, it is important that rfc4271 faithfully represent what the WG intended.  In this case, even though John didn’t say it explicitly, I would agree with him in considering that implementers may have already interpreted the text with the intent to not use the routes further.

I would like to get input from the WG as to the best way to handle this report.  I would specially like to hear from implementers, but all input is welcome.

The options are:

a. s/MAY NOT/may not
b. s/MAY NOT/MUST NOT
c. Rejecting the report.
d. Something else…

I will wait at least a week before proceeding.

Thanks!

Alvaro.



On 4/19/17, 1:37 PM, "RFC Errata System" <rfc-editor@rfc-editor.org> 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:
http://www.rfc-editor.org/errata_search.php?rfc=4271&eid=5000

--------------------------------------
Type: Technical
Reported by: John Scudder <jgs@juniper.net>

Section: 9.1.1

Original Text
-------------
      If the route is learned from an external peer, then the local BGP
      speaker computes the degree of preference based on preconfigured
      policy information.  If the return value indicates the route is
      ineligible, the route MAY NOT serve as an input to the next phase
      of route selection; otherwise, the return value MUST be used as
      the LOCAL_PREF value in any IBGP readvertisement.


Corrected Text
--------------
      If the route is learned from an external peer, then the local BGP
      speaker computes the degree of preference based on preconfigured
      policy information.  If the return value indicates the route is
      ineligible, the route MUST NOT serve as an input to the next phase
      of route selection; otherwise, the return value MUST be used as
      the LOCAL_PREF value in any IBGP readvertisement.


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". If a reader were to interpret this text as suggesting it is optional -- meaning, in effect, "the route MAY serve as an input to the next phase of route selection" -- that would be wrong and potentially problematic.

The minimal correction would be to use lower-case "may not", which makes the proper meaning reasonably clear. However, the English construct "may not" is notoriously ambiguous, therefore the proposed correction is "MUST NOT".

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  
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--------------------------------------
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