Hi Robert,
Thanks for your thorough comments. See below.
On Tue, Jun 28, 2016 at 3:33 PM, Robert Sparks <rjsparks(_at_)nostrum(_dot_)com>
wrote:
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Document: draft-ietf-trill-tree-selection-04
Reviewer: Robert Sparks
Review Date: 28 Jun 2016
IETF LC End Date: 1 Jul 2016
IESG Telechat date: 7 Jul 2016
Summary: Ready (with nits) for publication as Proposed Standard
This document is easy to read, even for someone not deeply steeped
in trill.
I have a few questions and suggestions to consider
1) The essence of the idea this document provides support for is that an
operator will create and install a configuration that meets the one tree per
identifiable thing (such as VLAN) constraint.
Well, it helps as long as multi-destination traffic identified by VLAN
or whatever is carried by fewer than all trees. It need not be one.
The protocol proposed here
does not try to enforce that the operator supplies a configuration meeting
that constraint. Should the things that generate messages with the TLVs
defined in this document be restricted from sending messages that would map
the same VLAN to two trees? I understand things will still work
(suboptimally, as pointed out in the backwards-compatibility section), but
it seems this configuration error should be mitigated. Section 3.3 also
pulls the punch a little with it's discussion at the end of the second
paragraph. If you're going to leave it up to the unspecified way the
operator installs this configuration, you might at least point out that this
is something to look for and complain about. If you think the optimal
configuration isn't a likely thing to reach, then consider a pass through
the document that sets that expectation consistently.
While restricting, for example, VLAN-x to one tree is optimal from the
point of view of using up the least amount of fast path FIB
(Forwarding Information Base) resources in some hardware
implementations, it is not optimal from the point of view of load
spreading. To get optimal load spreading, you would want to spread
different multi-destination flows onto different distribution trees.
2) There are a couple of places where you use 2119 where you appear to be
restating requirements from other documents. That's dangerous, from a
document set maintenance point of view. Please consider changing these to
simple prose, leaving the 2119 requirements to the protocol you're defining
in this document. Please look at the SHOULD in the Background Description,
and the SHOULD NOT in the first paragraph of the Overview. (2119 in sections
like backgrounds and overviews is usually a sign that somethings in the
wrong place.)
The SHOULD in the Background Description is indeed just echoing the
same provision from [RFC6325] and can be changed to not use a 2119 keyword.
The SHOULD NOT in the first paragraph of the Overview (Section 3.1) is
entirely due to theis draft and not inhereted from any other document.
3) In the 3rd paragraph of 3.3, why is the requirement SHOULD strength? What
else would the RBridge do, and when would it be reasonable for it to do that
something else?
The "SHOULD" requirement is to use a tree that the choosing RBridge
has advertised it will use; however, it is not actually required to
advertise which tree(s) it will use. Furthermore, even if it has, that
tree(s) might just have become unavailable due to one or more
failures. We can probably add some words to clarify that.
Nits/editorial comments:
* You use a lot of domain-specific acronyms in section 1 before saying what
they mean in section 2.
Looks to me like the terminology section could be moved up.
* The first sentence in the 8th paragraph of 1.2 is very
complex. (It's the one that starts "In cases where blocks
of"). Please consider simplifying it.
I think it can be re-worded.
* Section 2: (I'm no fun) Do you want this alternate expansion of
FGL to stand?
Nope... Looks like a global replace run amok or something, that should
be fixed :-)
* Figure 2: the left table has a VLAN of 4095, which is inconsistent
with the prose.
Shold be fixed. 4095 (0xFFF) is not a valid VLAN ID.
* In section 3.4 you use 2119 RECOMMENDED (which is equivalent to
SHOULD) when describing how the operator configures things. This
isn't a constraint on the protocol defined in this document. Please
consider rewriting the sentence without the 2119 keyword.
Humm. I think those are good operational recommendations. We can try
changing "RECOMMEND" to "suggest" and see if we get push back to
change it back :-)
* Micronits: there's spurious space at the beginning of the 3rd line
on page 6. There's an occurrence of BRridge that probably should
have been RBridge in section 3.4, and "assigne" appears in the IANA
Considerations.
OK.
Thanks,
Donald
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Donald E. Eastlake 3rd +1-508-333-2270 (cell)
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