Re: [trill] Genart LC (and likely telechat) review : draft-ietf-trill-tree-selection-04

Donald Eastlake <> Fri, 01 July 2016 14:43 UTC

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From: Donald Eastlake <>
Date: Fri, 1 Jul 2016 10:43:16 -0400
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To: Robert Sparks <>
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Subject: Re: [trill] Genart LC (and likely telechat) review : draft-ietf-trill-tree-selection-04
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Hi Robert,

A version -05 has been uploaded with the intent that it resolve your comments.

 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA

On Wed, Jun 29, 2016 at 4:09 PM, Donald Eastlake <> wrote:
> Hi Robert,
> Thanks for your thorough comments. See below.
> On Tue, Jun 28, 2016 at 3:33 PM, Robert Sparks <>
> wrote:
>> I am the assigned Gen-ART reviewer for this draft. The General Area
>> Review Team (Gen-ART) reviews all IETF documents being processed
>> by the IESG for the IETF Chair.  Please treat these comments just
>> like any other last call comments.
>> For more information, please see the FAQ at
>> <>.
>> 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
> ===============================
>  Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
>  155 Beaver Street, Milford, MA 01757 USA