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

🔓Dan Wing <dwing@cisco.com> Wed, 24 June 2015 07:53 UTC

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From: =?utf-8?Q?=F0=9F=94=93Dan_Wing?= <dwing@cisco.com>
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Date: Wed, 24 Jun 2015 00:52:52 -0700
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To: Owen DeLong <owen@delong.com>
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Cc: Vividh Siddha <vsiddha@apple.com>, v6ops@ietf.org
Subject: Re: [v6ops] Happy eyeballs suggestions, was: Re: Apple and IPv6, a few clarifications
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On 22-Jun-2015 02:53 pm, Owen DeLong <owen@delong.com> wrote:
> 
>> On Jun 22, 2015, at 13:50 , Iljitsch van Beijnum <iljitsch@muada.com> wrote:
>> 
>> On 22 Jun 2015, at 18:49, Owen DeLong <owen@delong.com> wrote:
>> 
>>>> So if you guys currently look at the RTT for the three-way handshake, it would probably help if you could look at the RTT for data packets instead.
>> 
>>> Pretty hard to look at the data RTT when establishing a connection. How do you see that working?
>> 
>> I don't know the details of Apple's (or anyone else's) happy eyeballs implementation. If they set up connections, measure the RTT for the three three-way handshake and then abandon the higher RTT session, or initiate connections in parallel and only pursue the one that connects first, then you're right, this would be a problem. On the other hand, if they do an HTTP request over IPv4 and one over IPv6, then an RTT for data segments would be available.
> 
> The few tcpdump logs I’ve looked at would seem to indicate that most (including Apple’s) HE implementations I’ve encountered do the former rather than the latter. Also as near as I can tell, state isn’t tracked from one connection to the next, each new connect() loop sprays a new set of SYNs and then abandons all but the one it selects.
> 
> YMMV

Best explanation of Apple's implementation is by Josh Graessley, who designed (and I believe also coded) the algorithm, http://lists.apple.com/archives/ipv6-dev/2011/Jul/msg00009.html.  Things have probably improved since 2011.

-d