Capwap Mailing List: Re: Issue 244: Preamble Header Optimization moved from Wish List to Active Issues Database

[Jim Murphy (jmurphy]

For a DTLS encrypted packet the format would look like this:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version| Type  |                    Reserved                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      DTLS hdr                                                 |
       .                                                               .
       .                                                               .
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version|  Type |  HLEN   |  RID    | WBID   |T|F|L|W|M|K|Flags |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Fragment ID          |     Frag Offset         |Rsvd |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 (optional) Radio MAC Address                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            (optional) Wireless Specific Information           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Payload ....                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Which is exactly the same as the -05 draft.

For a Non-DTLS encrypted packet the format would look like this:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Version|  Type |  HLEN   |  RID    | WBID   |T|F|L|W|M|K|Flags |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Fragment ID          |     Frag Offset         |Rsvd |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 (optional) Radio MAC Address                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            (optional) Wireless Specific Information           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Payload ....                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Note, in all these figures "|Version|  Type |" is replaced with
"|CAPWAP Preamble|" in the email referenced by Dorothy below.

So, no the proposal in issue 244 does not suffer from the above problem
since when DTLS is used it is exactly the same the -05 draft. The
version appears in both the shim and the encrypted CAPWAP header so
its value may be validated.

Thanks,

Jim

Pat Calhoun (pacalhou) wrote:
> Jim,
>
> I have a question about the proposal. One of the issues discussed two
> IETF face to face meetings ago, was that before the version field was in
> the clear, an attack could be mounted that would allow the changing of
> the outer version. It is for this reason that the version field was
> replicated in the capwap header, since it was protected by DTLS. 
>
> The proposal in issue 244 suffers from the above problem.
>
> I also presume that the "Reserved" field you show when DTLS is used
> would include the actual DTLS header, correct? Or are you instead
> proposing that the reserved field is optionally present, depending upon
> the value of the type field.
>
> PatC 
>
> -----Original Message-----
> From: Jim Murphy [mailto:jmurphy [at] trapezenetworks.com] 
> Sent: Wednesday, April 04, 2007 5:10 PM
> To: Dorothy.Gellert [at] nokia.com
> Cc: margaret [at] thingmagic.com; rbonica [at] juniper.net; capwap [at] frascone.com
> Subject: Re: [Capwap] Issue 244: Preamble Header Optimization moved from
> Wish List to Active Issues Database
>
> I support adopting the proposed optimizations.
>
> Thanks,
>
> Jim
>
> Dorothy.Gellert [at] nokia.com wrote:
> > Dear WG,
> >
> > While reviewing the recently closed issues, it appears that Issue 244,
>
> > Preamble Header Optimization, was mistakenly moved to the Wish list 
> > without a clear decision from the WG to do so.  As a result, we'll be 
> > moving issue 244 from the Wish list back into the "features" section 
> > of the database, so that the WG can further discuss this issue and 
> > decide what to do about it.  Issue 244 should be considered an open 
> > issue against the CAPWAP drafts.
> >
> > Issue 244 was discussed on the list under issue 224 before the interim
>
> > meeting, during the Interim meeting and again further discussed on the
>
> > WG list.  The proposed solution was sent to the list on Jan 31, 2007 
> > in this message:  
> > _http://lists.frascone.com/pipermail/capwap/msg04161.html_
> >
> > It does not appear that the WG made a decision on this issue either 
> > way, before it was moved to the Wish list, possibly because the 
> > discussion was lost inside a discussion of related issues.
> >
> > The WG should consider the proposed solution for Issue 244, and 
> > discuss the following alternatives on the WG list:
> >
> > 1) Adopt the proposed optimizations
> > 2) Reject the proposed optimizations
> > 3) Move Issue 244 to the Wish list (as this is an optimization, not a 
> > bug fix) for future consideration.
> >
> >
> > Best Regards,
> > Mani, Margaret and Dorothy
> >
> >
> > ----------------------------------------------------------------------
> > --
> >
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