RE: Mail regarding draft-litkowski-rtgwg-spf-uloop-pb-statement

[<[e-mail]>]

Hi Mike,

Thanks for this first review. I will for sure address your comments.
Some inline answers.

From: rtgwg [mailto:[e-mail]] On Behalf Of Mike Shand
Sent: Thursday, May 07, 2015 12:15
To: [e-mail]
Cc: [e-mail]
Subject: Re: Mail regarding draft-litkowski-rtgwg-spf-uloop-pb-statement

I have been assigned as Routing Directorate QA reviewer for this document.
The following web page contains a briefing on the QA process.
​https://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDirDocQa


The document provides a useful summary of the issues leading to micro-loop formation, especially in mixed vendor networks and provides examples of the possibilities to adversely affect the the micro-loop behaviour by inconsistent choices of parameters and algorithms among the routers in the network.
I confess that I find the timing diagrams quite hard to follow. One of the penalties of being constrained by the need to use ASCII art. But I wonder if something could be done to make them a little easier to follow without losing the essential information?
There are some very simple mitigation techniques, such as delaying the locally triggered  SPF/FIB installation more than a remotely triggered one, which it may be helpful to mention.

The document goes on to propose future work to standardise some behaviours.

Clearly this work is at an early stage and the trade-offs between standardisation and allowing vendors freedom to innovate for the benefit of their customers must be carefully considered.

The document seems like a good starting point for this work.


In reading the document I spotted a few items which it would be as well to address.

General:

1. micro-loop or microloop. The terminology is used inconsistently. RFC 5715 uses micro-loop
[SLI] Will be fixed

2. There are numerous instances of awkward usage of english. It would be helpful to address these at some stage.

Nits:

3. "   We will call SPF delay, the delay timer that exists in most
   implementations that makes codes to wait before running SPF
   computation after a SPF trigger is received."

The phrase "makes codes to wait" is somewhat contrived. How about "that specifies the required delay"?
[SLI] your proposal is fine, will be fixed


4. "   Routers have more and more powerful controlplane and dataplane that
   reduce the Control plane to Forwarding plane overhead during the
   convergence process.  Even if FIB update is still reasonably the
   highest contributor in the convergence time for large network, its
   duration is reducing more and more and may become comparable to
   protocol timers.  This is particular true in small and medium
   networks."

I don't understand what is meant by "may become comparable to protocol timers"? Are you suggesting that the FIB update latency WAS greater than the protocol timers, but has now been reduced to a comparable value?
[SLI] Right, even if it may be not true for all the networks, this tends to be the case

The reference to small and medium networks is also confusing, since in my experience it is actually the small and medium networks which are subject to the LARGEST FIB update times as a result of the deployment of under powered hardware.
[SLI] Yes and no …
I may say that small/medium networks have less powerful hardware, but also less routes (except badly designed networks ☺ ). Large network have more powerful hardware but more routes to handle.

5. "   In multi vendor networks, using different implementations of a link
   state protocol may favor micro-loops creation during convergence time
   due to deprecancies of timers."

deprecancies? Do you mean discrepancies?
[SLI] Yep, I meant “discrepancies” , will be fixed.


6. "4.2 Exponential Backoff"

"   o  First delay : amount of time to wait before running SPF.  This
      delay is used on when SPF is in fast mode."

I assume "is used only when SPF" is what you mean.
[SLI] Right, will be fixed


and similarly in the next bullet



Mike

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