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Re: [tsvwg] A review of draft-ietf-tsvwg-udp-options-12

Joseph Touch <touch@strayalpha.com> Sun, 13 June 2021 22:53 UTC

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From: Joseph Touch <touch@strayalpha.com>
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Date: Sun, 13 Jun 2021 15:53:28 -0700
Cc: Gorry Fairhurst <gorry@erg.abdn.ac.uk>, TSVWG <tsvwg@ietf.org>
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To: "C. M. Heard" <heard@pobox.com>
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Subject: Re: [tsvwg] A review of draft-ietf-tsvwg-udp-options-12
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> On Jun 13, 2021, at 3:00 PM, C. M. Heard <heard@pobox.com> wrote:
> 
> Responding to just this one specific point ...
> 
> On Sun, Jun 13, 2021 at 12:55 PM Joseph Touch wrote:
> And no, I do not think we should rely on RMSS to indicate that this is available. Note that a receiver would have to indicate RMSS and know the path MTU to know how many fragments it would actually take; we don’t require path MTU discovery for UDP options, so that’s an undue burden. Besides again injecting state into UDP.
> 
> 
> For IPv6 -- where fragmentation has the greatest issues

Why?

Effectively, both IPv4 and IPv6 currently support only source fragmentation. On-path has lots of problems.

> -- we are guaranteed a minimum MTU of 1280 bytes. A DNS server operating over IPv6 would be able to serve up a fragmented response with the right number of 1280 byte fragments (or else set the TC bit) if it received the MRSS option in the request from the client.

I’m speaking of a DNSSEC response, not just DNS.

Sure, in IPv6 the max number of fragments would be MRSS/(1280 - IP and UDP headers and options).

In IPv4, it arguably could be MRSS/(576 - headers).

But in both cases, it could be different for larger MSS.

Joe

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