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Re: Space for Packet Metadata

Gorry Fairhurst <gorry@erg.abdn.ac.uk> Wed, 28 February 2018 16:07 UTC

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Date: Wed, 28 Feb 2018 16:06:49 +0000
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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To: Nick Banks <nibanks@microsoft.com>
CC: "Eggert, Lars" <lars@netapp.com>, Mikkel Fahnøe Jør gensen <mikkelfj@gmail.com>, IETF QUIC WG <quic@ietf.org>
Subject: Re: Space for Packet Metadata
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For IPv6 that may be fine.

The QUIC transport paper (*) Section 7.1 speaks of "Packet Size 
Consideration"- as far as I know this is just UDP traffic from google 
Chrome clients to google servers. They showed 3% unreachable for 1200 B 
payloads. Other networks could well be different.

We are in the midst of a large measurement campaign related to our work 
in TSVWG on path MTU discovery. I would expect a wide variety of Path 
MTUs - even though the current majority of paths will support 1280 
bytes, many IPv4 paths do not - there are also many paths that support 
much more.

Gorry

* 
http://delivery.acm.org/10.1145/3100000/3098842/p183-Langley.pdf?ip=212.159.18.54&id=3098842&acc=OA&key=4D4702B0C3E38B35%2E4D4702B0C3E38B35%2E4D4702B0C3E38B35%2E5945DC2EABF3343C&__acm__=1519833743_fa365ff0c9cc6c6e266add2dba8f385f

On 28/02/2018, 15:30, Nick Banks wrote:
> According to spec, QUIC requires at least 1280 (from 9.4):
>
> "QUIC depends on the network path supporting a MTU of at least 1280 octets. This is the IPv6 minimum MTU and therefore also supported by most modern IPv4 networks. An endpoint MUST NOT reduce its MTU below this number, even if it receives signals that indicate a smaller limit might exist.'
>
> - Nick
>
> -----Original Message-----
> From: QUIC<quic-bounces@ietf.org>  On Behalf Of Eggert, Lars
> Sent: Wednesday, February 28, 2018 7:12 AM
> To: Mikkel Fahnøe Jørgensen<mikkelfj@gmail.com>
> Cc: IETF QUIC WG<quic@ietf.org>
> Subject: Re: Space for Packet Metadata
>
> On 2018-2-28, at 16:03, Mikkel Fahnøe Jørgensen<mikkelfj@gmail.com>  wrote:
>> Yes, but can it go below 1200? It seems the handshake aims to squeeze up near the minimum guaranteed (required) PMTU and QUIC implementations would probably not expect to maintain a connection that drops below PMTU 1200.
> The minimum IPv4 MTU is 576, so I'd expect QUIC stacks to probe as least that low.
>
> Lars

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