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
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"?
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?
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.
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?
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.
and similarly in the next bullet
Mike
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