Subject: [quicwg/base-drafts] Transport: (PL)PMTU text (#3217)

From: Gorry Fairhurst <[email-masked]>
Date: Mon, 11 Nov 2019 09:56:15 -0800

These comments relate only to the PMTU text in -24, relative to the current DPLPMTUD text as that now progresses to WGLC.

/This can also be used to construct PMTU probes (see
   Section 14.3.1). /
- Is this necessary? Or can padding frames be used to make (PL)PMTU probes?.
- My confusion here may be linked to not understanding the intent of 14.3.1

/Further validation can also be provided:

   o  An IPv4 endpoint could set the Don't Fragment (DF) bit on a small
      proportion of packets, so that most invalid ICMP messages arrive
      when there are no DF packets outstanding, and can therefore be
      identified as spurious.

   o  An endpoint could store additional information from the IP or UDP
      headers to use for validation (for example, the IP ID or UDP
      checksum)./
- I suggest the above text is spurious, since the checks advocated in DPLPMTUD and the QUIC fields provide a way to detect this. While it is possible too toggle the DF field, I do no think the IETF should endorse this, because it can have other side effects and this is not the place to propose that method.

/An endpoint MUST NOT increase PMTU based on ICMP messages.  /
- DPLPMTUD already specifies. This has always been the case, so please either delete or cite DPLPMTUD or the two core IP specs.

Section 14.3.1
I didn’t understand section 14.3.1. Maybe that isn’t good since I do understand PMTUD and PLPMTUD. Perhaps this section requires some reworking to explain the goal.

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