Re: [trill] Genart last call review of draft-ietf-trill-rbridge-multilevel-06

Donald Eastlake <> Wed, 28 June 2017 20:19 UTC

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From: Donald Eastlake <>
Date: Wed, 28 Jun 2017 16:18:49 -0400
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To: Stewart Bryant <>
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Subject: Re: [trill] Genart last call review of draft-ietf-trill-rbridge-multilevel-06
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Hi Stewart,

Thanks for the comments. See below.

On Wed, Jun 28, 2017 at 2:06 PM, Stewart Bryant
<> wrote:
> Reviewer: Stewart Bryant
> Review result: Ready
> 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-rbridge-multilevel-??
> Reviewer: Stewart Bryant
> Review Date: 2017-06-28
> IETF LC End Date: 2017-06-28
> IESG Telechat date: 2017-07-06
> Summary:
> This is a well written document. I do however have a concern with the scaling
> text in section 1.2.x, as I think this could be more accessible and ought to
> include discussion of MAC Address scaling. More information below.
> Major issues: None
> Minor issues: The key justification for multi-area is scaling. The scene is set
> in Section 1.2.x. However there are no references, the design size parameters
> are not articulated for each case, and the equations are not derived. I think
> that it would be helpful if the draft either provided some more explanation of
> the scaling equations and the associated input assumptions, or provided the
> assumptions and  directed the reader to an accessible text to understand the
> equations.

A reference and some further exposition of the assumptions made with
the way the equations were arrived at could be added.

>                     Although there is some discussion on it later there is no discussion
> of the number of addresses to be learned in the single and multi-area cases and
> the impact this has on the LSDB. The number of addresses to be learned will
> impact the ingress RBridge FIB and the FIB update time so this is just as
> significant in understanding the benefit of multi-level as understanding the
> link-state convergence time is.

The number of MAC (actually MAC/VLAN or MAC/FGL) addresses to be
learned by an edge TRILL switch is not affected by whether the TRILL
campus uses single or multilevel IS-IS. This number of MAC address
learned is the seventh scaling problem listed in Section 1.1 which
states that multilevel TRILL IS-IS helps only with the other six
problems. This point, that multilevel doesn't help here, could be
emphasized more but I don't think I see much point in this document in
going into details such as the scaling considerations of data plane
MAC address learning (which is the default in TRILL) or control plan
MAC address learning (which does not use the core LSDB but rather Data
Label scoped ESADI link stat databases).

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

> Nits/editorial comments: None