RE: Adam Roach's No Objection on draft-ietf-rtgwg-uloop-delay-07: (with COMMENT)

[<[e-mail]>]

Hi Adam,

Thanks for your review.
Some comments inline

-----Original Message-----
From: Adam Roach [mailto:[e-mail]] 
Sent: Wednesday, October 11, 2017 00:44
To: The IESG
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Adam Roach's No Objection on draft-ietf-rtgwg-uloop-delay-07: (with COMMENT)

Adam Roach has entered the following ballot position for
draft-ietf-rtgwg-uloop-delay-07: No Objection

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COMMENT:
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This document doesn't really define any new on-the-wire protocol. Was publication as a BCP rather than a standards track document considered?

The Introduction contains the following text:

   That means that all non-D
   neighbors of S on the topology will send to S any traffic destined to
   D if a neighbor did not, then that neighbor would be loop-free.

I can't parse this sentence. Is there supposed to be a sentence break somewhere in there?

[SLI] Good catch, Alvaro saw it also. A break is necessary between "D" and "if a neighbor".

The introduction starts talking about post-failure events (e.g., "when S converges to the new topology") before mentioning a failure of the S-D link.
This makes it very hard to follow. Would suggest mentioning the failure being considered before talking about the ensuing events.

[SLI] Right, I propose:
" Consider the case in Figure 1 where S does not have an LFA (Loop Free Alternate) to protect its traffic to D when the S-D link fails.  "


Section 4 begins:

   This document defines a two-step convergence initiated by the router
   detecting a failure and advertising the topological changes in the
   IGP.  This introduces a delay between the convergence of the local
   router and the network wide convergence.

This reads backwards to me. With this technique, the network converges first, followed by an introduced delay, followed by router convergence. Right?
[SLI] The network converges first, then the local router thanks to the introduced local delay.

Further on in that section:

   This benefit comes at the
   expense of eliminating transient forwarding loops involving the local
   router.

I can't make sense of this. Eliminating transient forwarding loops is a good thing, right? Not an expense?

[SLI] I think there is a missing word as we mean :" at the expense of eliminating the transient forwarding loops involving the local router ONLY".
I also agree that it's not really an expense , but more a limitation.
Here is a proposed rewording:
" This benefit comes with the limitation of eliminating transient forwarding loops involving the local router only"


I agree with Alvaro that the lack of a recommended default for ULOOP_DELAY_DOWN_TIMER is an issue, especially as the values configured in the examples seem to change arbitrarily from 1 second to 2 seconds.
[SLI] We cannot propose a default value that would fit all the situations. I agree that a statement is required in the Deployment Section to drive how the timer should be configured.

" The ULOOP_DELAY_DOWN_TIMER value should be set according to the maximum IGP convergence time observed in the network (usually observed in the slowest node)."


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