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Re: [tsvwg] UDP source ports for HTTP/3 and QUIC

Mark Nottingham <mnot@mnot.net> Thu, 22 July 2021 23:21 UTC

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From: Mark Nottingham <mnot@mnot.net>
In-Reply-To: <79d01f33-bc20-fce6-b49d-7c7cd67bea70@erg.abdn.ac.uk>
Date: Fri, 23 Jul 2021 09:21:06 +1000
Cc: "Black, David" <David.Black@dell.com>, Joseph Touch <touch@strayalpha.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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References: <3985895D-D420-4995-831E-332E33693B79@mnot.net> <CF409524-96F3-412A-A8DB-E4EFFDD9F4E7@mnot.net> <E62515E7-38FD-4197-8CF0-2D196FB6D6C4@strayalpha.com> <16CD883B-9561-41A5-97E0-43EF3618333C@mnot.net> <8235BE77-7849-49A3-A709-EB32EB039982@strayalpha.com> <AA5B1FC1-E0E8-488F-AE2E-F21696AD0A06@akamai.com> <MN2PR19MB4045E5063CE13DDE39D5BE8683E29@MN2PR19MB4045.namprd19.prod.outlook.com> <9263482C-2E0A-46F0-9351-B63C0E3B53E0@strayalpha.com> <MN2PR19MB40450ACCE13E4A335FF929A483E49@MN2PR19MB4045.namprd19.prod.outlook.com> <694559d2-c0ac-80f2-7336-950bf6384a9d@erg.abdn.ac.uk> <MN2PR19MB40454F6D65F78FD618C691E283E49@MN2PR19MB4045.namprd19.prod.outlook.com> <79d01f33-bc20-fce6-b49d-7c7cd67bea70@erg.abdn.ac.uk>
To: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tsvwg/fbekscBrfayXMhSwEOPx6NSYjrc>
Subject: Re: [tsvwg] UDP source ports for HTTP/3 and QUIC
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Hi Gorry,

> On 23 Jul 2021, at 7:14 am, Gorry Fairhurst <gorry@erg.abdn.ac.uk> wrote:
> 
> Am I understanding this about a client choosing source ports, and this client runs out of ephemeral ports (at least within the time it can reuse closed ports). I can see that servers can have lots of clients, but what is the use-case for a QUIC client to have that many open UDP ports? 

Please see my original mail in its entirety. There are two scenarios of note:

1) A client implementation asks the OS for a port and uses whatever it's given. Because of the port allocation practices of some implementations, the chosen port can be one of those we're talking about (although that's mostly for those > 1024). While AFAIK some implementations will try to allocate an ephemeral port number first (in the IETF definition), some will not, AIUI.

2) A client is behind a NAT/CGNAT that chooses a different source port, again within one of these ranges.

Cheers,

--
Mark Nottingham   https://www.mnot.net/

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