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Re: [tsvwg] UDP options and header-data split (zero copy)

Joseph Touch <touch@strayalpha.com> Sun, 01 August 2021 21:24 UTC

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From: Joseph Touch <touch@strayalpha.com>
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Date: Sun, 01 Aug 2021 14:24:20 -0700
Cc: tsvwg <tsvwg@ietf.org>
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To: Tom Herbert <tom@herbertland.com>
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Subject: Re: [tsvwg] UDP options and header-data split (zero copy)
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> On Aug 1, 2021, at 2:19 PM, Tom Herbert <tom@herbertland.com> wrote:
> 
> 
> 
> On Sun, Aug 1, 2021, 12:42 PM Joseph Touch <touch@strayalpha.com <mailto:touch@strayalpha.com>> wrote:
> 
> ...
> Had we limited the option length as a few suggested when this work started, we would not have FRAG.
> 
> We don’t know what others are, but we also don’t know that the first frag will have hundreds of bytes of available space either.
> 
> Actually, we do know that. The minimum MTU in IPv6 is 1280 and the minimum MTU for IPv4 is 576.

The min MTU for IPv4 is 68.

> If someone we're so inclined they could fill up the first fragment packet with nothing but options and start the payload in the second. That means you'll have at least 520 bytes for options.

That includes BOTH per-fragment and per-reassembled datagram options.

> But all this is academic since there's no use case other than DoS attack that would need anything close to that much space.

That was true until FRAG too. 

Again, this is a new decision - to limit the option space.

Joe

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