Re: [multipathtcp] q about on-path proxy

Olivier Bonaventure <Olivier.Bonaventure@uclouvain.be> Wed, 22 March 2017 10:13 UTC

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To: mohamed.boucadair@orange.com, Yoshifumi Nishida <nishida@sfc.wide.ad.jp>, multipathtcp <multipathtcp@ietf.org>
From: Olivier Bonaventure <Olivier.Bonaventure@uclouvain.be>
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Subject: Re: [multipathtcp] q about on-path proxy
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Med,


>         +------- R4 ---- R5 --------+
> C --- uMCP ---- R1 ---- R2 ------ dMCP ---- R6 --- R7 --- S



>>> Also, in the two proxy scenario, does the downstream MCP have to be
>>> on-path?
>>
>> If the downstream MCP is on path, then it does not have to include any
>> NAT function which is beneficial from an operational viewpoint.
>>
>>
>
> [Med] Perhaps I misunderstood your point but DNAT/SNAT are still needed for subsequent subflows even for the implicit case. Think about subflows that are placed with a destination address set to the one of the MCP and with a distinct source IP address than the one used to place the initial subflow.

By no NAT, I mean that all the packets between the client and the server 
that the operator would observe on the R1-R2 path or the R6-R7 path have 
C/S as source/destination addresses. This means that the existing 
techniques that are used for logging, traffic control or monitoring that 
depends on addresses can be reused without any modification.

When the uMCP creates a subflow towards the dMCP, it uses other 
addresses than C and S, but these addresses are invisible to both the 
client and the final server.

Olivier