Re: [multipathtcp] [Int-area] SOCKS 6 Draft

[Vladimir Olteanu <[e-mail]>]

On 07/19/2017 09:26 PM, Joe Touch wrote:
>
>
>
> On 7/14/2017 12:44 AM, Dragoș Niculescu wrote:
>>>> SOCKSv6 proposal makes use of extra data in the SYN (SOCKS data, and user data),
>>>> but
>>>> its correctness and backward compatibility does not depend on TFO, only its RTT
>>>> performance.
>>>> In fact, when TFO is not available neither between client and proxy, nor between
>>>> proxy and
>>>> server the SOCKSv6 RTT is still lower than SOCKSv4 and SOCKSv5. But TFO is
>>>> likely to be the most
>>>> common case in the future - Linux kernel has TFO client side on by default since
>>>> 3.12
>>>> (November 2013)[1], and it seems to be the default in all Android phones and
>>>> default
>>>> Linux installs.
>>> What happens with a legacy receiver?
>>>
>>> Joe
>> Legacy receiver will use plain TCP.
>
> No - a legacy receiver will interpret the SYN information as user 
> data, which there is no way to "undo".
>
> You can't know that you're not talking to a legacy receiver until you 
> receive the SYN-ACK. Even if you cache TFO availability, you could be 
> wrong - the endpoint could reboot or be replaced with a new endpoint, etc.
>
> Ultimately, the onus is on you to NEVER poison a TCP connection that 
> could be to a legacy receiver. That's a requirement in RFC793.
> Joe
>
I think there's a misunderstanding here. SOCKSv6 runs strictly on top of 
TCP. The "user data" to which we're referring is data meant to be 
relayed by the proxy to the server. The SYN's payload (both SOCKS 
request and said user data) is irrevocably part of the client-proxy data 
stream and we do not change it retroactively after learning that the 
proxy does not support TFO.

Vlad