Subject: [quicwg/base-drafts] Prohibit IP fragmentation (#3280)

From: Martin Thomson <[email-masked]>
Date: Mon, 02 Dec 2019 20:12:55 -0800

This won&#39;t necessarily prevent fragmentation from happening, but it&#39;s
the best we can do.  I didn&#39;t REQUIRE dropping of fragments, because
some systems do that for you, but a SHOULD seems appropriate.

Closes #3243.
You can view, comment on, or merge this pull request online at:

  https://github.com/quicwg/base-drafts/pull/3280

-- Commit Summary --

  * Prohibit IP fragmentation

-- File Changes --

    M draft-ietf-quic-transport.md (4)

-- Patch Links --

https://github.com/quicwg/base-drafts/pull/3280.patch
https://github.com/quicwg/base-drafts/pull/3280.diff

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From: Gorry Fairhurst <[email-masked]>
Date: Mon, 02 Dec 2019 23:39:40 -0800

gorryfair commented on this pull request.

> @@ -3471,6 +3471,10 @@ Datagrams containing Initial packets MAY exceed 1200 bytes if the client
 believes that the Path Maximum Transmission Unit (PMTU) supports the size that
 it chooses.
 
+UDP datagrams MUST NOT be fragmented at the IP layer.  In IPv4
+{{!IPv4=RFC0791}}, the DF bit MUST be set to prevent fragmentation on the path.
+Endpoints SHOULD discard fragmented IP packets.

I believe this is desirable at the receiving endpoint, but saying  "Endpoints SHOULD discard fragmented IP packets." ... isn't something that the transport has control over. I suggest you remove this. It seems sufficient to say at the sender don't do IPv4 or IPv6 fragmentation and do set FD

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From: Martin Thomson <[email-masked]>
Date: Wed, 04 Dec 2019 21:05:36 -0800

@martinthomson pushed 1 commit.

8ff17f071f05730a12049480dd9a8ffc97fb0b33  Remove fragmentation assembly recommendation

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From: ianswett <[email-masked]>
Date: Fri, 06 Dec 2019 09:38:20 -0800

ianswett approved this pull request.

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From: Jana Iyengar <[email-masked]>
Date: Fri, 06 Dec 2019 14:16:24 -0800

janaiyengar commented on this pull request.

> @@ -3471,6 +3471,9 @@ Datagrams containing Initial packets MAY exceed 1200 bytes if the client

That is not a requirement we can enforce, and it does not seem to be within QUIC's purview to require it. How about the following: "QUIC implementations are expected to ensure that UDP Datagrams containing QUIC packets are not fragmented by the IP layer at the sender. In IPv4 {{...}}, the DF bit MUST be set to prevent fragmentation on the path."

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