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Re: [Spud] [tsvwg] New Version Notification for draft-touch-tsvwg-udp-options-01.txt

Joe Touch <touch@isi.edu> Mon, 02 November 2015 15:29 UTC

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To: Tom Herbert <tom@herbertland.com>, Bob Briscoe <ietf@bobbriscoe.net>
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From: Joe Touch <touch@isi.edu>
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Subject: Re: [Spud] [tsvwg] New Version Notification for draft-touch-tsvwg-udp-options-01.txt
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On 11/1/2015 10:43 PM, Tom Herbert wrote:
> On Mon, Nov 2, 2015 at 3:05 PM, Bob Briscoe <ietf@bobbriscoe.net> wrote:
>> Joe,
>>
>> Before starting measurements, I would recommend searching the Web for the
>> manuals of middleboxes that might block such packets.
>>
> Please look at NIC offloads also. I am pretty certain that the most
> common flavor of checksum offload will break in this proposal since
> devices use the value in the UDP length field as the length of the
> payload to compute the checksum over. 

That is the intended behavior.

> UDP Fragmentation Offload would
> similarly be broken, although we can probably live without that (but
> we can't live without checksum offload!).

We need to live without broken offloads because offloads are part of the
protocol stack. They can't simply jump in and try to help without being
very careful about corner cases like this.

E.g., we've already seen an offload that merges TCP packets with
different options, which ought to be clearly inappropriate.

Joe

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