Re: [multipathtcp] q about on-path proxy

Yoshifumi Nishida <nishida@sfc.wide.ad.jp> Fri, 24 March 2017 18:07 UTC

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From: Yoshifumi Nishida <nishida@sfc.wide.ad.jp>
Date: Fri, 24 Mar 2017 11:07:02 -0700
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To: mohamed.boucadair@orange.com
Cc: Yoshifumi Nishida <nishida@sfc.wide.ad.jp>, "Olivier.Bonaventure@uclouvain.be" <Olivier.Bonaventure@uclouvain.be>, multipathtcp <multipathtcp@ietf.org>
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Subject: Re: [multipathtcp] q about on-path proxy
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Hi Med,

Thanks for the response.
Just one point..

On Thu, Mar 23, 2017 at 11:41 PM, <mohamed.boucadair@orange.com> wrote:

> Hi Yoshi,
>
>
>
> Please see inline.
>
>
>
> Cheers,
>
> Med
>
>
>
> *De :* Yoshifumi Nishida [mailto:nishida@sfc.wide.ad.jp]
> *Envoyé :* jeudi 23 mars 2017 23:38
> *À :* Olivier.Bonaventure@uclouvain.be; BOUCADAIR Mohamed IMT/OLN
> *Cc :* multipathtcp
> *Objet :* Re: [multipathtcp] q about on-path proxy
>
>
>
> Hello Olivier, Med,
>
>
>
> Thanks for providing detailed responses. I feel that things now got
> clearer than before.
>
> In my understanding, the benefits for on-path mode is MCP can stop
> intercepting and splitting connection once it learns that both endpoints
> support MPTCP.  if there're other benefits, please point out.
>
>
>
> One thing which is not very clear to me yet is MP_PREFER_PROXY.
>
> Med explained that there is a way to learn the endpoints support MPTCP. I
> think MCPs can learn it through the method described in Figure 15, however
> I'm not sure how the sender can learn it.
>
> [Med] An implementation example would look like the following :
>
> ·         A sends a SYN message with MP_CAPABLE+MP_PREFER_PROXY to B
>
> ·         This SYN is intercepted by an MCP which tracks the connection,
> that is: it removes the MP_PREFER_PROXY and add filters to intercept
> relevant incoming SYN/ACK. The SYN (MP_CAPABLE) is then forwarded to the
> next hop and so on, until it reaches B.
>
> ·         If the SYN/ACK received from B includes MP_CAPABLE, the MCP
> will forward it to A. A is now aware that B is MPTCP-capable and they can
> establish subsequent subflows directly. The MCP does not announce
> explicitly itself to A.
>

Hmm. I am not sure about this.
I understand A will receive MP_CAPABLE from B in this case. But, I think
even B doesn't support MPTCP, A will receive MP_CAPABLE from B which is
created by MCP (by spoofing). So, I think A cannot identify whether this is
from B or MCP.
--
Yoshi

>