RE: BFD stability follow-up from IETF-91

[Santosh P K <[e-mail]>]

Manav,
   Thanks. Please see inline comments.

> You could use the crypto sequence numbers carried in the meticulous
> cryptographic auth for detecting packet losses. However, this breaks when
> you use non-meticulous crypto authentication since the sequence number is
> only incremented occasionally there. This i believe is a deal breaker since i
> really envision non meticulous mode to be the one being widely deployed. In
> fact we were supposed to write a draft on that and i guess it just fell through
> the cracks (lemme ping my co-author on that !)
> 
> One way to solve this problem is by attaching a debug trailer that only carries
> the seq numbers at the *end* of the BFD packet. This would not be covered
> in the Length field carried in the BFD header but would be accounted for in
> the length carried in the IP header. The concept of attaching a trailer is
> documented well and is used in the IGPs. RFC 6506 describes one such trailer

You are suggesting to add the debug trailer with or without authentication right? 


> for OSPFv3. The catch however is that this debug trailer will NOT be covered
> by the BFD authentication. Is this acceptable to the WG?

I did not get this. Did you mean the length of the auth TVL will not include this length and will be only in IP header? 

> I think the problem of diagnosing a BFD flap becomes all the more important
> with BFD authentication turned on since then we have more points where a
> delay can be inserted.

I agree with this and as a developer have seen this happening. 

Thanks
Santosh P K 

> On Thu, Nov 27, 2014 at 8:32 PM, Santosh P K <[e-mail]>
> wrote:
> > Manav,
> >     This is good question.
> >
> >> Can the authors add some text on how this debugging mechanism would
> >> work if somebody employs BFD authentication?
> >
> > Right now we have considered without authentication (we are setting A
> bit). We should add some text on how we can use both Auth and de bug TLV.
> Is there any suggestion you have? I will get back to you on this.
> >
> >
> > Thanks
> > Santosh P K
> >
> >> > -----Original Message-----
> >> > From: Rtg-bfd [mailto:[e-mail]] On Behalf Of Mach
> >> > Chen
> >> > Sent: Thursday, November 27, 2014 2:13 PM
> >> > To: Marc Binderberger
> >> > Cc: [e-mail]
> >> > Subject: RE: BFD stability follow-up from IETF-91
> >> >
> >> > Hi Marc,
> >> >
> >> >> -----Original Message-----
> >> >> From: Marc Binderberger [mailto:[e-mail]]
> >> >> Sent: Thursday, November 27, 2014 1:43 AM
> >> >> To: Mach Chen
> >> >> Cc: Manav Bhatia; [e-mail]
> >> >> Subject: RE: BFD stability follow-up from IETF-91
> >> >>
> >> >> Hello Mach,
> >> >>
> >> >> > This triggers me think out there should be another solution for
> >> >> > getting the Tx and Rx timestamps without encoding the timestamps
> >> >> > in the BFD
> >> >> packets.
> >> >> > For example, the Tx and Rx systems could just save timestamps
> >> >> > locally or send them to a centralized entity and then use the
> >> >> > sequence numbers to correlate them for further analyzing.
> >> >>
> >> >> I remember some discussion on NVO3 about how many bits it takes
> >> >> ;-) - could you send the links/draft names you are working on to this
> list?
> >> >> May be useful for further discussions.
> >> >
> >> > Sure, here is the
> >> > link(http://tools.ietf.org/html/draft-chen-ippm-coloring-
> >> based-ipfpm-framework-02) for the reference.
> >> >
> >> > But here I want to say is that since we have sequence number, we
> >> > may not
> >> need the marking based solution. Suppose that someone want to monitor
> >> the delay of a BFD packet , just record and save the timestamp at the
> >> Tx side, which indexed by the sequence number. Similarly, do the same
> >> at the Rx side. Then based on the timestamps from both Tx and Rx, and
> >> using the sequence number to correlate the timestamps, it can also
> >> provide a way to monitor the delay of the BFD packet.
> >> >
> >> > That means, only if there is sequence number, even if without
> >> > carrying the
> >> timestamp in the BFD packet, BFD packet delay can be measured.
> >> >
> >> > Best regards,
> >> > Mach
> >> >
> >> >>
> >> >>
> >> >> Thanks & Regards,
> >> >> Marc
> >> >>
> >> >>
> >> >>
> >> >> On Wed, 26 Nov 2014 09:17:32 +0000, Mach Chen wrote:
> >> >> > Hi Marc and Manav,
> >> >> >
> >> >> >> -----Original Message-----
> >> >> >> From: Rtg-bfd [mailto:[e-mail]] On Behalf Of
> >> >> >> Marc Binderberger
> >> >> >> Sent: Wednesday, November 26, 2014 4:50 PM
> >> >> >> To: Manav Bhatia
> >> >> >> Cc: [e-mail]
> >> >> >> Subject: Re: BFD stability follow-up from IETF-91
> >> >> >>
> >> >> >> 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.
> >> >> >
> >> >> > Yes, this is one solution if people think BFD delay is needed.
> >> >> > If allow to have Tx timestamps to be carried in the packets,
> >> >> > seems it should be no problem to leave a seat for the Rx
> >> >> > timestamps as well :-). After all, with both Tx and Rx
> >> >> > timestamp, it may simplify the
> >> >> implementation.
> >> >> >
> >> >> >>
> >> >> >> 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.
> >> >> >
> >> >> > Indeed, the sequence number helps a lot for the correlation
> >> >> > between the Tx and Rx system.
> >> >> >
> >> >> > This triggers me think out there should be another solution for
> >> >> > getting the Tx and Rx timestamps without encoding the timestamps
> >> >> > in the BFD
> >> >> packets.
> >> >> > For example, the Tx and Rx systems could just save timestamps
> >> >> > locally or send them to a centralized entity and then use the
> >> >> > sequence numbers to correlate them for further analyzing.
> >> >> >
> >> >> > Best regards,
> >> >> > Mach
> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> 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.ppt
> >> >> >>>> x
> >> >> >>>>
> >> >> >>>> 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
> >> >> >>>>
> >> >> >>>
> >> >> >
> >> >
> >