Re: [multipathtcp] potential MPTCP proxy charter item

Joe Touch <touch@isi.edu> Wed, 09 November 2016 14:51 UTC

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From: Joe Touch <touch@isi.edu>
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To: mohamed.boucadair@orange.com
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Subject: Re: [multipathtcp] potential MPTCP proxy charter item
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> On Nov 9, 2016, at 2:07 AM, <mohamed.boucadair@orange.com> <mohamed.boucadair@orange.com> wrote:
> 
> Re-,
>  
> There are two cases :
> ·         UC#1 : MPTCP Client=================MPTCP Proxy----Server
> ·         UC#2 : Client---CPE(MPTCP Proxy)==== MPTCP Proxy----Server
>  
> For UC#1, I don’t see why the same port number will be returned by the OS given that TIME_WAIT is not expired.

TCP is asked to connect once. You seem to now expect it to try twice - TCP cannot (it can't pick ports by itself) and user land cannot be expected to or may not be able to.

>  
> Since the MPTCP Proxy in UC#2 is tracking TCP connections (TCP/MPTCP glue), it is the responsibility of the MPTCP Proxy to select the source port to use. This is similar to a NAT function. We are leveraging on the TCP BEHAVE recommendations.

 It might not be able to use the source port it wants either.

Joe


>  
> Cheers,
> Med
>  
> De : Joe Touch [mailto:touch@isi.edu] 
> Envoyé : mercredi 9 novembre 2016 10:00
> À : BOUCADAIR Mohamed IMT/OLN
> Cc : Mirja Kühlewind; Olivier.Bonaventure@uclouvain.be; multipathtcp@ietf.org
> Objet : Re: [multipathtcp] potential MPTCP proxy charter item
>  
>  
>  
> 
> You've just opened a connection using a pair of ports. You sent a RST, but RSTs are not reliable. So you can't reuse that port pair until TIME-WAIT expires.
> 
> [Med] This a fair observation. Another source port number will be used for the fallback connection (if any).  
> 
> That is no longer TCP.
> Remember that it is not TCP that picks these ports. The OS does when the user didn't but the user can.
>  
> Joe