Re: Preparing for discussion on what to do about the multipath extension milestone

[Martin Duke <[e-mail]>]

The concerns that Christian and MT raise are the same ones I was alluding
to, but I do think a draft like this one that adds the necessary bits of
protocol to enable multipath experimentation is the right scope. I don't
feel strongly whether we should adopt this and fix it, or fix it and then
adopt it.

Martin

On Thu, Oct 1, 2020 at 1:23 AM Martin Thomson <[e-mail]> wrote:

> I share Christian's concerns about the draft, but it's not just ACKs, it's
> the entire Uniflow concept that I would call into question.
>
> On Thu, Oct 1, 2020, at 17:25, Christian Huitema wrote:
> > I am not sure that the current "mpquic" draft is the right approach.
> > Specifically, I do not agree that having one packet number space per
> > path is the right approach. This contradicts the design of QUIC V1, in
> > which data sent on multiple paths shares a common packet number space.
> > For example, in QUIC V1, we can start a connection on one path, migrate
> > to another path, and keep the same packet number space throughout. I
> > find that a very nice property -- and also an essential property if we
> > want to support NAT rebinding. Handling multipath with a single number
> > space requires some book-keeping on the sender side to match
> > acknowledgements and sending paths, but we have working code for that.
> >
> > I am also not convinced that we properly understand the concept of
> > "path". There is very little in the QUIC V1 protocol that requires
> > transmission paths to be symmetric: any packet sent from a node to a
> > valid address of the peer will be accepted, provided the crypto works.
> > The linkage such requirement comes from the statement that a server
> > starts directing traffic to a validated path when it sees the client
> > using the same pair of addresses. This is an "implicit" linkage; I
> > would expect that the first role of a multipoint extension would be to
> > replace that by an "explicit" statement of preferences.
> >
> > I am worried that we have a set of unresolved security issues around
> > paths, largely linked to the requirement to support NAT rebinding. If
> > we support NAT, the IP headers must be outside the authentication
> > envelope of the crypto. There are plausible attacks in which the
> > attacker splices a cryptographically valid packet and a forged IP
> > header. We have some defensive heuristics, but if we study multipath I
> > hope we will end up with something better.
> >
> > -- Christian Huitema
> >
> > On 9/30/2020 5:51 PM, Ian Swett wrote:
> > > Given the responses, can we narrow down the way forward(ideally on a
> different thread) to directions that are less open-ended?  I'll suggest
> some options, but the chairs and/or ADs need to decide.
> > >  1) No future work on multipath in the QUIC WG, in the belief the
> existing connection migration functionality is sufficient.
> > >  2) Adopt the existing draft as a starting point for QUIC
> multipath(draft-deconinck-multipath-quic <
> https://tools.ietf.org/html/draft-deconinck-multipath-quic>), with the
> explicit goal of not expanding the scope of the document.
> > >  3) Adopting multipath as a core QUIC WG deliverable.
> > >
> > > I favor #2, but these may not be the right options.  Normally I'd say
> people should work this out in person, but that doesn't seem viable at the
> moment.  I'm happy to set up a long(3-4+hr) Google Meet to discuss this via
> videoconference if that helps move the discussion forward.
> > >
> > > Or we can form a design team, which typically takes O(3 months) to
> finish.
> > >
> > > Ian
> > >
> > > On Wed, Sep 30, 2020 at 3:15 PM Spencer Dawkins at IETF <
> [e-mail]> wrote:
> > >> Hi, Martin,
> > >>
> > >> Just a couple of thoughts here:
> > >>
> > >> On Wed, Sep 30, 2020 at 12:16 PM Martin Duke <[e-mail]>
> wrote:
> > >>> (Speaking as an individual)
> > >>>
> > >>> There is some back-and-forth as to whether these are useful cases
> are not. I'll take it on faith, given the proponents, that there is a real
> hope of deploying this. However, I share the desire to not have the WG
> fully consumed by MP-QUIC for the foreseeable future.
> > >>
> > >> That sounds right. I'm assuming that getting the core QUIC
> specifications published and doing any cleanup work necessary SHOULD/MUST
> take priority, in the BCP 14 sense of those words.
> > >>
> > >> As Lars' initial note said, I'd also like to see the manageability,
> applicability, and datagram extension working group drafts, already adopted
> by QUIC, moving forward.
> > >>
> > >>> I don't think the community has well-established solutions for many
> problems in this space (e.g. scheduling). However, I think QUIC is a far
> better platform for experimentation than the alternatives, and would
> support a draft similar to draft-deconinck-multipath-quic <
> https://tools.ietf.org/html/draft-deconinck-multipath-quic> that provided
> the required protocol extensions to make that happen [1].
> > >>
> > >> I agree that scheduling is challenging - 3GPP is certainly spending
> time defining different strategies for behaviors, even in addition to the
> ones we described in
> https://datatracker.ietf.org/doc/draft-bonaventure-quic-atsss-overview/.
> > >>
> > >> And I agree that the QUIC protocol would be a better platform for
> experimentation than anything I can think of (other suggestions are, of
> course, welcome).
> > >>
> > >>> IIUC the hard, unsolved problems are common to all MP protocols, so
> I don't think further research and future standards in this area are
> specific to QUIC or appropriate for the QUIC Working Group. But
> experimental QUIC extensions would accelerate this work, are appropriate
> for the WG, and may get us to a place where we could confidently develop
> standards about it.
> > >>
> > >> Targeting Experimental status for work in this area sounds like a
> fine plan to me (much better than not thinking about multicast in the IETF
> for a while longer).
> > >>
> > >> I know you have a variety of tools at your disposal to direct this
> work (MP-TCP was done in its own working group, for both Experimental and
> Standards-Track versions of the protocol specifications). Do the right
> thing, of course.
> > >>
> > >> What do you and Magnus need from members of the community, to help
> move forward on this?
> > >>
> > >> Best,
> > >>
> > >> Spencer
> > >>
> > >>> Martin Duke
> > >>>
> > >>> [1] I would prefer that this draft be Experimental, and have
> numerous nits about the design that are not relevant to this thread.
> > >>
> > >>
>
>