Subject: [Errata Held for Document Update] RFC5880 (4410)

From: RFC Errata System <[email-masked]>
Date: Tue, 16 Feb 2016 12:26:08 -0800 (PST)

The following errata report has been held for document update 
for RFC5880, "Bidirectional Forwarding Detection (BFD)". 

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=5880&eid=4410

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Status: Held for Document Update
Type: Editorial

Reported by: Liu Lin <[email-masked]>
Date Reported: 2015-07-07
Held by: Alvaro Retana (IESG)

Section: 6.8.4

Original Text
-------------
If Demand mode is active, and a period of time equal to the Detection
Time passes after the initiation of a Poll Sequence (the transmission
of the first BFD Control packet with the Poll bit set), the session
has gone down

Corrected Text
--------------
If Demand mode is active, and a period of time equal to the Detection
Time passes after the initiation of a Poll Sequence (the transmission
of the first BFD Control packet with the Poll bit set),and without 
receiving a BFD Control packet with the Final (F) bit set from the
remote system, the session has gone down

Notes
-----
If has received BFD Control packet with the Final (F) bit set from the
remote system, the session will not gone down

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RFC5880 (draft-ietf-bfd-base-11)
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Title               : Bidirectional Forwarding Detection (BFD)
Publication Date    : June 2010
Author(s)           : D. Katz, D. Ward
Category            : PROPOSED STANDARD
Source              : Bidirectional Forwarding Detection
Area                : Routing
Stream              : IETF
Verifying Party     : IESG

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From: Jeffrey Haas <[email-masked]>
Date: Tue, 16 Feb 2016 15:59:25 -0500

I do not believe the errata in question is necessary.

Section 6.8.4 covers the calculation of the detection interval.
After the start of a poll, the remote system may take some time to respond
to the poll and set the Final bit.  During that time, it is permissable to
send Async packets following the packet reception rules - including
authentication - without setting the Final bit.  

The text recommended by this proposed errata constrains this time to the
completion of a Poll within the originally negotiated detection interval.
While this may happen, it is not required.

-- Jeff (speaking as an individual contributor)

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From: Marc Binderberger <[email-masked]>
Date: Sun, 28 Feb 2016 17:56:23 -0800

Hello Jeff and BFD experts,

> authentication - without setting the Final bit.  

really?

the "demand mode" part of 6.8.4 talks about the local system being in demand 
mode, if I understand it correctly. This means the remote system MUST NOT 
send packets periodically, unless the remote system itself started a Poll 
sequence. See 6.8.7, paragraph 7.

So for 6.8.4 the local system would not expect any async packets from the 
remote side other than a packet with the "F" bit, as this exception is 
allowed for the remote system.

There is also section 6.6, saying:

   When a system in Demand mode wishes to verify bidirectional
   connectivity, it initiates a Poll Sequence (see section 6.5).  If no
   response is received to a Poll, the Poll is repeated until the
   Detection Time expires, at which point the session is declared to be
   Down.  Note that if Demand mode is operating only on the local
   system, the Poll Sequence is performed by simply setting the Poll (P)
   bit in regular periodic BFD Control packets, as required by section
   6.5.

One could argue what "no response" means but as it says "the Poll is 
repeated" and knowing how the Poll sequence works (6.5) it seems to be the 
"F" bit packet that the local system needs to receive.

Saying all this I still agree with you that the errata is not necessary. What 
the errata wants to say is already said in RFC5880. We probably could pick 
many paragraphs in RFC5880 and point out sentences that by themselves are not 
sufficient - ubt are okay in the context of the overall document.

Regards, Marc