Re: [v6ops] Happy eyeballs suggestions, was: Re: Apple and IPv6, a few clarifications

Iljitsch van Beijnum <> Tue, 23 June 2015 00:30 UTC

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Date: Tue, 23 Jun 2015 02:29:52 +0200
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Subject: Re: [v6ops] Happy eyeballs suggestions, was: Re: Apple and IPv6, a few clarifications
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On 23 Jun 2015, at 2:17, Owen DeLong <> wrote:

>> But IPv6 UDP applications shouldn't concern themselves with testing for PMTUD black holes. This breaks TCP anyway, giving the user much bigger fish to fry. And IPv4 UDP applications should leave the DF bit alone because setting it to one can only end in tears.

> And once again, Iljitsch lets religion get in the way of understanding the way the real world works…

That would be true if I were talking about IPv4 UDP applications not testing for PMTUD black holes. Which I also stand behind; the internet needs larger packets, so any action to artificially limit packet sizes is counterproductive.

But my point about IPv6 UDP applications is not religious, it's just simple common sense: if the protocol that occupies 85% of the internet's packets is going to fail anyway, why bother doing extra work to keep one particular application that occupies a small fraction of the remaining 15% running? (I.e., with unlike with IPv4, with IPv6, TCP and UDP have the same failure mode in the presence of PMTUD black holes. And if depending on PMTUD is too deemed dangerous, then 1280 is the answer, with no need for any testing.)