Re: [Idr] Bug in draft-ietf-idr-rfc5575bis, worth fixing?

Susan Hares <> Thu, 24 September 2020 19:11 UTC

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From: Susan Hares <>
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Date: Thu, 24 Sep 2020 15:10:56 -0400
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Subject: Re: [Idr] Bug in draft-ietf-idr-rfc5575bis, worth fixing?
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John, Alvaro, Christoph,  and Danny: 


I agree with Alvaro that the document covers the unknown case.   

However,  it is fine to add the text to tie the information down. 


I do not think we need to take this back to the WG – as I believe the text covers this point already. 


Sue Hares


From: Idr [] On Behalf Of Alvaro Retana
Sent: Wednesday, September 23, 2020 5:37 PM
To: John Scudder; idr@ietf. org
Cc:; Hares Susan
Subject: Re: [Idr] Bug in draft-ietf-idr-rfc5575bis, worth fixing?






Personal opinion:  I believe that the “specified here” part (meaning this document) is already covering the unknown case.  However, I have no objections to adding the phrase in.







On September 23, 2020 at 5:14:50 PM, John Scudder ( wrote:

Hi All, 


I’m a little concerned about a change I failed to notice earlier in 5575bis. Version 17 had this paragraph in Section 4.2:


   All combinations of component types within a single NLRI are allowed,
   even if the combination makes no sense from a semantical perspective.
   If a given component type within a prefix in unknown, the prefix in
   question cannot be used for traffic filtering purposes by the
   receiver.  Since a Flow Specification has the semantics of a logical
   AND of all components, if a component is FALSE, by definition it
   cannot be applied.  However, for the purposes of BGP route
   propagation, this prefix should still be transmitted since BGP route
   distribution is independent on NLRI semantics.


Version 18 removed the paragraph. I believe it was removed because of good and reasonable concerns about the “prefix should still be transmitted” part. But, it appears we threw out the baby with the bathwater: the final version of the draft has nothing that corresponds to the underlined part. It is underspecified with respect to what should be done with unknown component types. The closest it comes is this paragraph in Section 4.2 of version 26:


   A NLRI value not encoded as specified specified here is considered
   malformed and error handling according to Section 10 <>  is performed.


But I think this falls well short of being either clear or unambiguous, because what does “as specified here” mean exactly? 


I’d like to open a discussion of whether the WG agrees that this is a bug and if so, whether it’s concerning enough to request a last-minute patch to the document, which is currently with the RFC Editor, so it’s almost an RFC. I think the least intrusive fix would be to insert the clause “including an NLRI that contains an unknown component type”, as in:


   A NLRI value not encoded as specified here,
   including an NLRI that contains an unknown component type,
   is considered
   malformed and error handling according to Section 10 <>  is performed.


Just as a side note, “error handling according to Section 10” points us to RFCs 7606 and 4760, which end up telling us to reset the session if the NLRI is malformed.


Until we get a chance to discuss this, I’ve sent a note to the RFC Editor asking them to hold publication.






P.S.: The version 26 text also has a proofreading error, “specified specified”. But I assume the RFC Editor would fix that anyway.