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RE: Can I set the UDP checksum to zero when running QUIC?

"Shihang(Vincent)" <shihang9@huawei.com> Wed, 13 March 2024 09:13 UTC

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From: "Shihang(Vincent)" <shihang9@huawei.com>
To: Christian Huitema <huitema@huitema.net>, Martin Thomson <mt@lowentropy.net>
CC: "quic@ietf.org" <quic@ietf.org>
Subject: RE: Can I set the UDP checksum to zero when running QUIC?
Thread-Topic: Can I set the UDP checksum to zero when running QUIC?
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Date: Wed, 13 Mar 2024 09:13:47 +0000
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Hi Christian,
The idea of trial is interesting. I wonder if the trial should be done per path or per end host? Are you assuming some middleboxes will mess up the NULL checksum UDP packets?

Thanks,
Hang

-----Original Message-----
From: QUIC <quic-bounces@ietf.org> On Behalf Of Christian Huitema
Sent: Wednesday, March 13, 2024 12:51 PM
To: Martin Thomson <mt@lowentropy.net>; quic@ietf.org
Subject: Re: Can I set the UDP checksum to zero when running QUIC?

One the other hand, the cost of computing the checksum is tiny compared to the cost of encrypting the packets. So there is a small performance gain in not computing the checksum, compensate by the potential gain of loosing compatibility.

If I were to do that, I would do some trials. Until the handshake is complete, use the checksum. Then, send a trial packet with null checksum. If the peer acknowledges it, then further packets can be sent with null checksum. Redo the trial for each new path, or if there are large number of packet losses. Basically, treat that the same way we do PMTUD.

-- Christian Huitema

On 3/12/2024 3:57 PM, Martin Thomson wrote:
> The question is more of a compatibility one than anything else.  What, if anything breaks if you do this?
> 
> As noted, there are contexts in which not computing the checksum works.  So I guess the conclusion is that nothing breaks, so go ahead.  QUIC doesn't depend on the checksum.  All the cryptographic bits of QUIC use far stronger and more reliable mechanisms.
> 
> On Tue, Mar 12, 2024, at 22:04, Shihang(Vincent) wrote:
>> Hi QUIC wg,
>> Since QUIC has strong encryption and integrity protection provided by 
>> TLS 1.3. I wonder if the UDP checksum can be disabled(using UDP Zero 
>> Checksum Mode https://www.rfc-editor.org/rfc/rfc6936 )to save the 
>> computation just like in VXLAN(RFC7348 
>> <https://datatracker.ietf.org/doc/html/rfc7348#autoid-12>).
>>
>> Thanks,
>> Hang
>

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