Re: [multipathtcp] Consensus call on potential MPTCP proxy work

Joe Touch <> Tue, 18 April 2017 13:30 UTC

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Subject: Re: [multipathtcp] Consensus call on potential MPTCP proxy work
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Hi, all,

The description below isn't sufficient to determine whether this work is
either needed or safe.

My initial conclusion is that this work is either (a) not needed at all,
(b) out of scope, or (c) involves one if not two very bad ideas.

I have a few questions that determine which of (a), (b), or (c) apply
(below), but I've already commented on my concerns that conclude (c)
*based on previously assuming this was intended as an IP tunnel and used
an option with control plane info in the SYN data) so I won't repeat them.

I am curious as to what's really intended here, though.


1) what is the reason for needing MPTCP work to support proxy-proxy use?
True proxies are applications and can already setup MTCP themselves.
Protocols for operators to configure proxies seem out of scope here. And
if this "proxy" path is really an IP tunnel, that's a very bad idea (TCP
over TCP), which I already noted in previous discussion.

2) what does "using the transfer a signalling message"
mean? Are you using the MPTCP control plane? or the data plane of the
MPTCP connection?

3) I'm not sure I fully understand the details of the optinns, but I
understand that at least one of them puts data in the SYN that is
interpreted as something other than TCP data (i.e., control plane). That
is also a very bad idea - it interferes with MPTCPs ability to silently
fall-back to TCP when talking to legacy endpoints, and the reasons for
not using TCP data as control are discussed in draft-ietf-tcpm-tcp-edo,
Section 8.7 (and are the reason for draft-touch-tcpm-tcp-syn-ext-opt),
which I also already noted in previous discussion.

On 4/18/2017 1:17 AM, wrote:
> Hi,
> During the MPTCP meeting in Chicago we did several hums about
> potential MPTCP proxy work. Our interpretation of these hums is that
> we should do a consensus call for the following work:
> --
> MPTCP is now seeing widespread deployment in networks to bond together
> two accesses, such as fixed and mobile broadband, by using two MPTCP
> proxies, one in the home gateway or Customer Premises Equipment and
> one in the network. The WG develops a solution where the proxies are
> both under the control of the operator and where it is assumed that
> they are not on the default path. The solution is based on using the
> payload of an MPTCP packet to transfer a signalling message between
> the proxies. It is believed the solution will not require changes to
> RFC6824bis. The solution may require a means of configuring set-up
> information in the proxies, which would be done in coordination with
> other IETF WGs such as DHC. The WG does not develop a mechanism for
> the two proxies to discover each other.
> --
> Please say whether you support, or don’t support, such work – so we
> can see if there’s consensus for it.
> Thanks
> Phil & Yoshi
> Hums during the meeting:
> ·         Should the MPTCP WG do any MPTCP proxy work, or do none –
> about 2:1 or 3:1 in favour of doing work
> ·         Should the MPTCP WG do proxy work based on option #1 in
> slide 12? Strongly more yes than no
> ·         Should the MPTCP WG do proxy work based on option #2 in
> slide 12? more no than yes
> ·         Should the MPTCP WG do proxy work based on option #3 in
> slide 12? Weak & roughly equal
> Ref:
> We believe the work does not require an update to the MPTCP WG charter.
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