Re: [tsvwg] Adoption call: draft-fairhurst-tsvwg-datagram-plpmtud-02 to end 10th January 2018

Christian Huitema <huitema@huitema.net> Wed, 10 January 2018 18:23 UTC

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From: Christian Huitema <huitema@huitema.net>
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Date: Wed, 10 Jan 2018 08:22:50 -1000
Cc: "Eggert, Lars" <lars@netapp.com>, "Black, David" <David.Black@dell.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>, QUIC WG <quic@ietf.org>
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To: gorry@erg.abdn.ac.uk
Subject: Re: [tsvwg] Adoption call: draft-fairhurst-tsvwg-datagram-plpmtud-02 to end 10th January 2018
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> On Jan 10, 2018, at 5:38 AM, Gorry Fairhurst <gorry@erg.abdn.ac.uk> wrote:
> ...
> 
> I suspect someone could use the final method with QUIC - since it's also a UDP-based transport. I don' knopw of anyone planning PMTUD for QUIC - please get in touch if that is on your radar.

The initial packets in QUIC are sent with min IPv6 MTU. During the initial exchange, the nodes send the maximum packet size that they might accept. QUIC does not specify the actual probing algorithm but does specify that PMTU is per path.

Several QUIC implementations do PMTUD already, building simple probes with QUIC's Ping and Padding frames. Probes are then encrypted, and sent as QUIC packets in UDP with segmentation turned off. If the probe packet is acknowledged, the applications know that this much MTU can be sent.

Note the encrypted part. Replacing such mechanisms by a clear text exchange is not desirable.

-- Christian Huitema