Subject: Re: Correcting BFD Echo model

From: Jeffrey Haas <[email-masked]>
Date: Fri, 24 Mar 2017 11:46:40 -0400

[continuing the top-posting heresy to preserve context]

Greg,

Our schedule is relatively open right now, and this matter is esoteric
enough that it probably warrants a slide for the majority of the Working
Group to follow this issue.  Would you prepare a slide or two to use as a
discussion point?

I'll also use this opportunity to point out that in S-BFD scenarios, we have
somewhat similar ambiguities since it's an on-demand service.

-- Jeff

On Mon, Feb 27, 2017 at 07:31:01AM -0800, Greg Mirsky wrote:
> Hi Reshad,
> thank you for providing the context to BFD Echo TX. Indeed, I'm familiar
> with implementations that use BFD Echo as Echo request/reply and thus Tx
> would be in RPC, not in configuration. I think that it would be good to
> discuss this in Chicago unless we hear comments from others on the list.
> 
> Regards,
> Greg
> 
> On Mon, Feb 27, 2017 at 5:56 AM, Reshad Rahman (rrahman) <[email-masked]>
> wrote:
> 
> > Hi Greg,
> >
> > draft-zheng-mpls-ls-ping-yang-cfg defines transmit interval in RPC
> > because all ping operations are done via RPC.  I do not consider BFD echo
> > to be “on demand” like LSP Ping (caveat: this is possibly due to the BFD
> > configuration/implementation I am most familiar with).

---

From: Greg Mirsky <[email-masked]>
Date: Fri, 24 Mar 2017 13:50:04 -0500

Hi Jeff,
I'll be glad to put couple slides to help jumstart the discussion on BFD
Echo.

Regards,
Greg

---

From: "Carlos Pignataro (cpignata)" <[email-masked]>
Date: Fri, 24 Mar 2017 18:59:21 +0000

Hi, Greg,

It would be useful to understand uses of BFD Echo for on-demand scenarios.

It’s not clear how that would be:

   When a system is using the Echo function, it is advantageous to
   choose a sedate reception rate for Control packets, since liveness
   detection is being handled by the Echo packets.  This can be

Thanks,

— Carlos.

On Mar 24, 2017, at 2:50 PM, Greg Mirsky <[email-masked]<mailto:[email-masked]>> wrote:

Hi Jeff,
I'll be glad to put couple slides to help jumstart the discussion on BFD Echo.

Regards,
Greg

On Fri, Mar 24, 2017 at 10:46 AM, Jeffrey Haas <[email-masked]<mailto:[email-masked]>> wrote:
[continuing the top-posting heresy to preserve context]

Greg,

-- Jeff

On Mon, Feb 27, 2017 at 07:31:01AM -0800, Greg Mirsky wrote:
> On Mon, Feb 27, 2017 at 5:56 AM, Reshad Rahman (rrahman) <[email-masked]<mailto:[email-masked]>>
> wrote:
>
> > Hi Greg,
> >

---

From: Greg Mirsky <[email-masked]>
Date: Fri, 24 Mar 2017 14:09:17 -0500

Hi Carlos,
indeed, the RFC 5880 does explain that the rate of BFD control packets
transmitted in Async mode may be reduced when Echo is activated. If anyone
is familiar with such implementation, I'd be glad to learn and discuss how
this mechanism affects the data model. Regrettably, I don't have personal
experience with using or implementing such mechanism.

Greg

On Fri, Mar 24, 2017 at 1:59 PM, Carlos Pignataro (cpignata) <
[email-masked]> wrote:

> On Mar 24, 2017, at 2:50 PM, Greg Mirsky <[email-masked]> wrote:
>
> Hi Jeff,

---

From: Jeffrey Haas <[email-masked]>
Date: Fri, 24 Mar 2017 15:28:58 -0400

> On Mar 24, 2017, at 3:09 PM, Greg Mirsky <[email-masked]> wrote:
> 
> Hi Carlos,
> indeed, the RFC 5880 does explain that the rate of BFD control packets transmitted in Async mode may be reduced when Echo is activated. If anyone is familiar with such implementation, I'd be glad to learn and discuss how this mechanism affects the data model. Regrettably, I don't have personal experience with using or implementing such mechanism.

My *suspicion* is that the configuration would represent a set of parameters for both async mode and echo mode.  These will not alter themselves automatically.

The operational mode might reflect timers that have backed off.  However, this is also true if an implementation does various forms of session auto-tuning.  An example I'm aware of is a decrease in timer aggressiveness as part of a high availability switchover event.

-- Jeff

---

From: "Reshad Rahman (rrahman)" <[email-masked]>
Date: Fri, 24 Mar 2017 22:35:42 +0000

I am familiar with an implementation which supports echo and reduces rate
of control packets when echo is enabled. In that implementation, the
configuration has desired interval and multiplier, there isn¹t different
timer configurations for async and echo. Echo is enabled by default but
there is config knob to disable echo. The operational model does show the
rates at which control and echo packets are being transmitted.

But back to Greg¹s original question, I¹d like to hear from other BFD
implementations which support echo. Is echo enabled "on demand² e.g. For a
small duration like ping, or is it continuous?

Regards,
Reshad.

On 2017-03-24, 3:28 PM, "Jeffrey Haas" <[email-masked]> wrote:

>>transmitted in Async mode may be reduced when Echo is activated. If
>>anyone is familiar with such implementation, I'd be glad to learn and
>>discuss how this mechanism affects the data model. Regrettably, I don't
>>have personal experience with using or implementing such mechanism.
>
>My *suspicion* is that the configuration would represent a set of
>parameters for both async mode and echo mode.  These will not alter
>themselves automatically.
>
>The operational mode might reflect timers that have backed off.  However,
>this is also true if an implementation does various forms of session
>auto-tuning.  An example I'm aware of is a decrease in timer
>aggressiveness as part of a high availability switchover event.
>
>-- Jeff
>

---

From: Greg Mirsky <[email-masked]>
Date: Sun, 26 Mar 2017 12:47:27 -0500

Hi Jeff, et. al,
attached are two slides to remind how RFC 5880 describes BFD Echo and its
use, per my understanding. As well as outline of two models to present Echo
BFD in data model. Appreciate your comments, suggestions. Will be glad to
update the slides or feel free to hop on and edit them directly.

Regards,
Greg