Re: BFD stability follow-up from IETF-91

[Marc Binderberger <[e-mail]>]

Hello Manav,

> I believe the work is important and addresses something thats really
> required (spent too much time debugging why BFD flapped!).

agree :-) we should keep the discussion alive.


> side Time stamping would have helped in debugging whether the BFD
> packet was sent late, or whether the packet was sent on time and also
> arrived on time but was delayed when passing it up the BFD
> stack/processor (lay in the RX buffer for tad too long)

well, I can see a point in having the Tx timestamps in the packet mainly for 
the purpose of knowing "this" packet was okay/not okay on the Tx side and to 
correlate it with your local Rx measurement.

And even this point is less relevant with sequence numbers as this number 
allows the identification of packets and thus the correlation of information 
from the Tx and Rx system.


Regards, Marc






On Wed, 26 Nov 2014 12:26:41 +0530, Manav Bhatia wrote:
> Hi Jeff,
> 
> I vividly remember the original intent of the stability draft was to
> help debug BFD failures -- to isolate the issue at the RX or the TX
> side Time stamping would have helped in debugging whether the BFD
> packet was sent late, or whether the packet was sent on time and also
> arrived on time but was delayed when passing it up the BFD
> stack/processor (lay in the RX buffer for tad too long), etc. But then
> time stamping came with its own set of issues, and was hence dropped
> from the original draft.
> 
> Can the authors send a summary on the list on why time stamping was
> dropped so that we're all clear on that one.
> 
> The current proposal does help but is not complete.
> 
> Assume that the RX end loses a BFD session and learns later that it
> did eventually receive the missing BFD packets (based on the seq #).
> How would it know which end was misbehaving? Was it a delay at the TX
> side, or was it the RX that delayed passing the packets to the BFD
> process(or). This is usually what we want to debug and i want to
> understand how this draft with sequence numbers can unequivocally tell
> me that.
> 
> I believe the work is important and addresses something thats really
> required (spent too much time debugging why BFD flapped!). Clearly
> what would help is putting a small section that describes how we can
> use the sequence numbers to debug what and where things went wrong.
> 
> Cheers, Manav
> 
> 
> On Wed, Nov 26, 2014 at 5:49 AM, Jeffrey Haas <[e-mail]> wrote:
>> draft-ashesh-bfd-stability-01 was presented again during IETF-91 in
>> Honolulu.  The slides can be viewed here:
>> 
>> http://www.ietf.org/proceedings/91/slides/slides-91-bfd-4.pptx
>> 
>> To attempt to simplify the presentation, the contentious portion of the
>> timers were removed from the proposal, leaving only the sequence numbering
>> for detecting loss of BFD async packets.
>> 
>> When the room was polled to see whether the draft should be adopted as a WG
>> item, the sense of the room was very quiet.  As promised, this is to 
>> inquire
>> for support for this draft on the WG mailing list to make sure the whole
>> group has a voice.
>> 
>> It should be noted that post-meeting discussion on the fate of this draft
>> noted that BFD authentication code points are plentiful and are available
>> with expert review.  Should the draft authors wish to continue this work as
>> Experimental, that is an option.
>> 
>> -- Jeff
>> 
>