Adam Roach's No Objection on draft-ietf-6man-rfc1981bis-06: (with COMMENT)
Adam Roach <adam@nostrum.com> Thu, 11 May 2017 04:20 UTC
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From: Adam Roach <adam@nostrum.com>
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Subject: Adam Roach's No Objection on draft-ietf-6man-rfc1981bis-06: (with COMMENT)
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Adam Roach has entered the following ballot position for draft-ietf-6man-rfc1981bis-06: No Objection When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-6man-rfc1981bis/ ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- I'd like to add my voice to the concerns expressed regarding RFC2119 language. I understand the desire to only deal with the changed parts of the specification; but the current process as I understand it is that bis versions of document are expected to be "brought up to code" according to modern IETF document practices. Perhaps we should have a conversation about whether that practice is in need of revising, but I'm not sure making piecemeal exceptions is the best way to go about starting that conversation. In any case, I believe that current practice is that new RFCs cite 2119 and adhere to its definitions when using these specific terms in all-caps; and that this will be published as a new RFC. Minor technical comment: Like others, I also had a really hard time with the paragraph in section 4 concluding with "MUST force the Path MTU Discovery process to end." It's difficult to read this as anything *other* than "you get one Path Too Big, and just shut down discovery," but that's clearly not what the rest of the document says. (I'll also note that if we are treating capital "MUST" as normative, then "MUST attempt to" is kind of meaningless). Minor technical comment: Section 5.4 has three paragraphs, starting "Alternatively, the retransmission could be done in immediate response to a notification" that propose a more aggressive means of dealing with packets lost to PMTU issues; most of this text is a warning about how this can go awry and (if you'll excuse a bit of hyperbole) melt the Internet. Given that the first alternative works just fine and appears to be much safer, is this alternative actually something we want to recommend for today's implementations? The remainder of my comments are editorial. The second-to-last paragraph of the introduction uses the phrase "such messages" in a way that makes the antecedant difficult to find. I spent a while trying to figure out how PMTUD used TCP three-way-handshakes or blackholed TCP packets to determine PMTU. Suggest: "..relies on ICMPv6 messages to determine..." The abbreviation "PTB" appears in the second paragraph of section 4. I would ordinarily suggest expanding on first use; but as this is this first and only use, I suggest simply replacing it with the long form used in the rest of the document. Section 5.1 introduces the term MMS_S, and relates it to EMTU_S. I note that the former is not in the terminology section, while the latter is -- I suspect that they should both be present. Section 5.2 uses the acronym "ECMP". I would suggest citing the related document in which ECMP is defined and optionally expanding the acronym. Section 5.2 indicates: Also, the instance that sent the packet that elicited the Packet Too Big message should be notified that its packet has been dropped, even if the PMTU estimate has not changed, so that it may retransmit the dropped data. It is quite nonintuitive how this situation could arise: if the packet is of size X, and the PMTU has not changed, then it follows that X <= PMTU (as the packet would have been reduced in size otherwise). If the PMTU has not changed, it also follows that PMTU <= MTU (from the Packet Too Big message). it follows that X <= MTU (from the Packet Too Big message), and so it really should not have been dropped unless the corresponding router has an implementation flaw of some kind. More importantly, it would seem that an attempt to transmit another packet of size X at this point would run an overwhelmingly high chance of triggering another Packet Too Big for whatever errant reason caused the first one to be sent. I'm sure this naïve explanation overlooks whatever nonintuitive situation is envisioned by this paragraph. It would be quite helpful if such a situation were described: I, as an implementor, would look at this and say "What? No. I'm not doing that. It's extra work for no benefit." I suspect it will be dealt with by the RFC editor, but the first normative reference seems to have some kind of issue with the production of the authors' names. I see several acknowledgements in section B.1 that will be removed prior to publication. The authors may wish to consider moving these names to section 7 for the sake of posterity.