Re: [trill] Routing directorate QA review of draft-ietf-trill-rfc6439bis

"Joel M. Halpern" <> Sun, 03 July 2016 19:30 UTC

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To: Donald Eastlake <>
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From: "Joel M. Halpern" <>
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Date: Sun, 3 Jul 2016 15:30:10 -0400
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Subject: Re: [trill] Routing directorate QA review of draft-ietf-trill-rfc6439bis
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Thanks Donald.  Looks good to me.

On 7/3/16 1:53 PM, Donald Eastlake wrote:
> Hi Joel,
> Thanks for your comments.
> Because this draft happens to be close to expiring and we are coming
> up on the refractory period before the Berlin meeting, I'm going to do
> my best at editing it based on your comments and upload a revision.
> But if that does not resolve your comments, further changes can be
> made.
> See below.
> On Sun, Jun 26, 2016 at 8:58 PM, Joel M. Halpern <> wrote:
>> This is a QA review, intended to provide an additional perspective,
>> requested by the TRILL chairs and Routing ADs.
>> The reviewer understands that the WG last call has completed, and hopes that
>> this review will prove helpful to the working group.
>> [For clarity, the above is written before performing the review.]
>> This document is ready for publication as a Proposed Standard RFC.
>> Major: N/A
>> Minor: N/A
>> Nits:
>>     Section 2.2 base has two bullet items.  the first appears to be a subset
>> of the second.  Is this deliberate?
> You are correct. I guess as an author I thought of the second point as
> being more restricted than the words actually are. I was thinking it
> actually said something like "When it observes a change in DRB on the
> link from one RBridge other than itself to another RBridge other than
> itself." However, it seems like it would be clearer to re-write that
> small section of text.
>>     The counter-example at the end of the second paragraph of section 2.4
>> seems to be missing some limitation that would explain it.  (It is possible
>> this is more obvious to a reader who is more conversant with TRILL, but
>> there does seem to be something missing.)
> Maybe the wording isn't very clear. Let me describe the counter
> example somewhat more verbosely in different words.
>      Say that all the end stations in a TRILL campus that are in
> VLAN-x are attached to RBridge-1.  That means that they are on links
> that is attached to RBridge-1 and there might be one or more other
> RBridges attached to those links. (Note that in TRILL, a link can be a
> bridged LAN.) On each such link, there will be a Designated RBridge
> election to chose the RBridge that is in charge of end station traffic
> on that link, either ingressing/egress such traffic itself or
> assigning it to one or more other RBridges on that link by VLAN.
>      Assume that RBridge-1 is overloaded. Thus RBridge-1 will
> typically do a poor job of forwarding traffic, because it cannot hold
> the complete topology. Normally, you would not want RBridge-1 handling
> end station traffic. If RBridge-1 wins the DRB election on a link, it
> should assign the handling that traffic to other non-overloaded
> RBridges on its links, if such RBridges are available, and if some
> other RBridge on a link wins the DRB election, it should not assign
> the handling of such traffic to RBridge-1.
>      However, in the case of VLAN-x traffic, all the end stations in
> VLAN-x have local connectivity to RBridge-1. The inability of
> RBridge-1 to do a good job forwarding traffic is immaterial to traffic
> in VLAN-x because it will never have to forward it because all end
> stations in VLAN-x are local. Thus, even through RBridge-1 is in
> overload, it SHOULD be assigned the handling of end station traffic
> for VLAN-x.
> I'll try to clarify the wording in the draft.
>> Editorial:
>>     In section 10.4 defining the FGL-VLAN Mapping Bitmap APPsub-TLV, the
>> diagram calls the fifth field "Starting FGL".  The text below that refers to
>> it the field simply as "FGL".  I believe the text should also name it
>> "Starting FGL".
> OK.
>> Side note: I really appreciate the thorough additional explanations as to
>> the reasons various actions are safe or unsafe.  Thank you.
> You're welcome,
> Donald
> ===============================
>  Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
>  155 Beaver Street, Milford, MA 01757 USA
>> Yours,
>> Joel M. Halpern