Re: [storm] MPA Draft - Review

"Hemal Shah" <> Thu, 31 March 2011 18:43 UTC

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From: "Hemal Shah" <>
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Date: Thu, 31 Mar 2011 11:43:46 -0700
Thread-Topic: MPA Draft - Review
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Subject: Re: [storm] MPA Draft - Review
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I have some comments on -03 draft:

1.      In section 10, it is written that "Enhanced MPA Initiator and Responder:  If a responder receives an enhanced MPA message, it MUST respond with an unenhanced MPA message." I think it should be written that the responder must respond with an enhanced MPA message. It appears like a typo to me.
2.      I find the use of FULPDU confusing in this draft. RFC5044 does not define term FULPDU. RFC5044 uses term FPDU to refer to Framed Protocol Data Unit. I suggest that we use term FPDU instead of FULPDU in the draft.


-----Original Message-----
From: [] On Behalf Of
Sent: Thursday, March 31, 2011 7:48 AM
Subject: Re: [storm] MPA Draft - Review
Importance: High

The -03 version of the MPA draft has addressed all of the issues from my review, and .  Unfortunately, I need some minor edits for clarity before I can send this on to our AD with a publication request.  Would the authors please submit a -04 version with the following two changes quickly.

Section 9 (end)


   The peer-to-peer negotiation for the RTR message follows the
   following order:

   Initiator -->: Sets Control Flags it is capable to send for RTR

   Responder <--: Sets Control Flags it is capable to receive for RTR

   Initiator -->: The first message send MUST be a negotiated RTR


   The peer-to-peer negotiation for the RTR message follows the
   following order:

   Initiator -->: Sets Control Flags to indicate Initiator-supported forms of RTR

   Responder <--: Sets Control Flags to indicate Responder-supported forms of RTR

   Initiator -->: If at least one form of RTR is supported by both Initiator and
        Responder, then the first message sent MUST be an RTR using a form supported
        by both the Initiator and Responder.

Section 10

      this case initiator CAN attempt to establish RDMA connection using
      unenhanced MPA protocol as defined in [RFC5044] and let ULP deal
      with ORD and IRD, and peer-to-peer negotiations.


      this case initiator MAY attempt to establish RDMA connection using
      unenhanced MPA protocol as defined in [RFC5044] if this protocol is
        compatible with the application, and let ULP deal with ORD and IRD,
      and peer-to-peer negotiations.

Ordinarily, I'd write an RFC Editor Note for small changes like these, but they're sufficiently critical to interoperability that I'd prefer to have a new draft version that contains them.


> -----Original Message-----
> From: Black, David
> Sent: Wednesday, December 22, 2010 9:26 PM
> To:
> Cc: Black, David
> Subject: MPA Draft - Review
> WG Last Call on this draft has run its course:
>                  Enhanced RDMA Connection Establishment
>                   draft-ietf-storm-mpa-peer-connect-02
> I've done my review as a WG chair (and the person who will be shepherding this draft to the ADs and
> IESG):
> - This draft is on the right track, but has open issues.
> - Another version of the draft will be needed.
> Also, it would be greatly appreciated if a few people other than the authors could take a look at
> this draft.  We have a very good author team on this draft, whose expertise is beyond doubt, but
> more eyes on this draft would help.
> [1] My primary concern is that Section 9 on interoperability is inadequate:
>    An initiator SHOULD NOT use the Enhanced DDP Connection Establishment
>    formats or function codes when no enhanced functionality is desired.
>    A responder SHOULD continue to accept the unenhanced connection
>    requests.
> The good news is that the first sentence is ok.
> The bad news is that the second sentence has significant problems:
>       - It uses SHOULD instead of MUST.
>       - It doesn't lay out behavior for initiator and responder
>               Revision mixes.
> IETF interoperability requirements are usually expressed with MUST, including backwards
> compatibility.  If interop with unenhanced implementations is only a SHOULD, that will need a
> convincing explanation.
> There are 3 Initiator/Responder cases that need attention (New/Old, Old/New and New/New).  I think
> they lead to roughly the following:
> New/Old:
> - Explain error or failure that the New Initiator will see because the Old responder
>       doesn't support Revision 2 of the MPA protocol.
> - Explain what the Initiator does when it sees that error or failure.  The
>       easiest approach is to always retry with Revision 1, but that won't work
>       if the Initiator has to send an RTR (that's the "convincing explanation"
>       for why backwards compatibility is not always possible).  The result
>       might be two requirements:
>       - If the Initiator has data to send, it MUST retry with Revision 1.
>       - If the Initiator has no data to send, and hence has to send an RTR,
>               the connection setup fails, the TCP connection closes and that
>               failure MUST to be reported to the application.
> Old/New:
> - If a responder receives a Revision 1 message, it MUST respond with a Revision 1 message.
> New/New:
> - If a responder receives a Revision 2 message, it MUST respond with a Revision 2 message.
> I found a few other concerns:
> [B]In Section 7, we need to get the listing of all the SCTP function codes into one place.  Either
> repeat the definitions of codes 1-4 from RFC 5043, or create an IANA registry in Section 10 and list
> all 7 codes as its initial contents.
> [C] In Section 8, what happens if the responder sends an IRD or ORD value that's different from the
> corresponding initiator value?  Is the responder allowed to increase the value that was sent?  An
> important case to cover is that the initiator sends a valid value (e.g., 0x2000) but the responder
> returns the 0x3FFF value indicating that negotiation is not supported.  Also, what is the behavior
> of an IRD or ORD that is set to 0x0000?
> [D] In contrast, the Section 8 discussion of Control Flag functionality is in better shape.  It
> would be helpful to add a sentence or two indicating when the RTR occurs (Request ->, <- Reply, RTR
> ->), even though that is discussed earlier in the draft.  Also, it's necessary to state whether
> negotiation of RTR functionality commits the Initiator to using an RTR (e.g., suppose the initiator
> negotiates control flags to allow an RTR and instead sends an FULPDU with payload data after
> receiving the Reply - is that ok or is it an error?).
> [E] Nit: In the definition of Control Flag A: ULPDU -> FULPDU
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> +1 (508) 293-7953             FAX: +1 (508) 293-7786
>        Mobile: +1 (978) 394-7754
> ----------------------------------------------------

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