Early Review of draft-litkowski-rtgwg-spf-uloop-pb-statement-02
I have been assigned as Routing Directorate QA reviewer for this
The following web page contains a briefing on
the QA process.
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
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
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
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.
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.
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
reduce the Control plane to Forwarding plane overhead during
convergence process. Even if FIB update is still reasonably
highest contributor in the convergence time for large network,
duration is reducing more and more and may become comparable to
protocol timers. This is particular true in small and medium
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
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.
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