Re: [DMM] Warren Kumari's Discuss on draft-ietf-dmm-mag-multihoming-04: (with DISCUSS)

[Warren Kumari <[e-mail]>]

On Wed, Aug 2, 2017 at 5:18 PM <[e-mail]> wrote:

> Hello
>
> Please see inline
>
> Pierrick
>
>
>
> Sent from my cell phone, mind the typos.
>
> -------- Message d'origine --------
> De : Warren Kumari <[e-mail]>
> Date : 02/08/2017 22:23 (GMT+01:00)
> À : The IESG <[e-mail]>
> Cc : [e-mail], Jouni Korhonen <
> [e-mail]>, [e-mail], [e-mail],
> [e-mail]
> Objet : Warren Kumari's Discuss on draft-ietf-dmm-mag-multihoming-04:
> (with DISCUSS)
>
> Warren Kumari has entered the following ballot position for
> draft-ietf-dmm-mag-multihoming-04: Discuss
>
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> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about IESG DISCUSS and COMMENT positions.
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> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-dmm-mag-multihoming/
>
>
>
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
>
> Section 3.2.  Traffic distribution schemes
> "Per-packet management: the LMA and the MAG distribute packets, belonging
> to a
> same IP flow, over more than one bindings (i.e. more than one WAN
> interface)."
> This immediately made my out-of-order-packets antenna pop up, so I read the
> section looking for mitigations. The very next sentence reads: "Packet
> distribution can be done either at the transport level, e.g. using MPTCP
> or at
> When operating at the IP packet level, different packets distribution
> algorithms are possible. " -- the fact that this sentence is a: malformed
> and
> b: hand-wavy did nothing to allay my concerns, so I read further: "The
> distribution algorithm is left to implementer but whatever the algorithm
> is,
> packets distribution likely introduces packet latency and out-of-order
> delivery.  LMA and MAG shall thus be able to make reordering before packets
> delivery." - I agree with the first sentence (although it is poorly
> worded),
> but the second sentence doesn't follow from the first; "shall thus be able
> to"
> implies that the prior text somehow provides a solution, not points out a
> problem (the sentence is also malformed)-- I think you mean something like
> "The
> LMA and MAG thus need to be able reorder packets to their original order
> before
> delivery."
>
> This then continues with "Sequence number can be can be used for that
> purpose,
> for example using GRE with sequence number option [RFC5845]." - I think
> that
> the actual reference should be RFC2890, but regardless of this, I don't
> think
> that what you are proposing works - "The Sequence Number field is used to
> maintain sequence of packets **within** the GRE Tunnel." (from RFC2890,
> emphasis added). This means that sequence numbers are local to the tunnel,
> and
> (as I understand it) your solution involves diverse tunnels. Further,
> Section
> 2.2. Sequence Number says: "The receiver may perform a small amount of
> buffering in an attempt to recover the original sequence of transmitted
> packets. In this case, the packet may be placed in a buffer sorted by
> sequence
> number." - if you are proposing using a single sequence number space for
> multiple tunnels, you will end up with sequence number space gabs, and
> lots of
> buffering, etc. The section ends with: "However, more detailed
> considerations
> on reordering  and IP packet distribution scheme (e.g. definition of
> packets
> distribution algorithm) are out the scope of this document." - I think
> that,
> unless the prior paragraph is significantly reworked, it should not try and
> suggest any mitigations.
>
> >> ok
>
>
> The whole idea of striping packets of a flow across (notably) different
> transports seems like a really bad idea to me -- is it actually needed?
>
> >> some use-cases implement per-packet distribution. However this document
> does not aim to make recommendation on the way to distribute packets
>
>
So, how do they deal with out of order packets?
W


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> --
I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of
pants.
   ---maf