Capwap Mailing List: Re: Last call comments for capwap-protocol-binding-ieee80211-07

[Pasi.Eronen (Pasi.Eronen]

Pat Calhoun wrote:

> > > > This is contradicted by text in e.g. Section 6.15, 
> > > > which requires 
> > > > the WTP to process (beyond copying to beacons) the IE received
> > > > from 
> > > > AC even in Split MAC mode.
> > > 
> > > OK, fair enough. That is one exception, but that one is 
> > > described in
> 
> > > the spec. The spec even includes:
> > > 
> > > <current text>
> > > 2.2.1.  Split MAC
> > > [...]
> > > 
> > >    o  The WTP generates the IEEE 802.11 Beacon frames, using 
> > >       information
> > >       provided to it through the IEEE 802.11 Add WLAN (see 
> > >       Section 6.1)
> > >       message element, including the RSNIE, which 
> > >       indicates support of 802.1X and AES-CCMP.
> > > </current text>
> > 
> > Yes, but the spec isn't very clear on how the RSN IE exactly is
> processed by the WTP (the IE has number of different fields).
> 
> The WTP does not need to perform any processing of the RSN IE. The
> IE is included in the Beacon and Probe Responses as-is by the
> WTP. Any cryptographic policies are sent by the AC either through
> the Add Station or the Session Key message elements. 

By "processing", I meant the WTP has to parse the contents of the RSN
IE, find some field(s) inside it, and use those value(s) for something.
Both Sections 6.1 and 6.15 say the WTP does this; I'd like to see
more details for "some field(s)" and "something".

(Presumably, other IEs are just stored and copied to Beacons and Probe
Responses -- the WTP doesn't need to parse them. Is this correct?). 

> So in order to provide more clarity, I propose adding the first
> sentence in the last paragraph of the following text:
> 
> <modified text>
> 6.1.  IEEE 802.11 Add WLAN
> [...]
>   Power Constraint information element
> 
>    EDCA Parameter Set information element
> 
>    QoS Capability information element
> 
>    WPA information element  [WPA]
> 
>    RSN information element
> 
>    WMM information element  [WMM]
> 
>    These IEEE 802.11 information elements are stored by the WTP and
>    included in any Probe Responses and Beacons generated, as specified
>    in the IEEE 802.11 standard [IEEE.802-11.2007].  If 
>     present, the RSN
>    information element is sent with the IEEE 802.11 Add WLAN message
>    element to instruct the WTP on the usage of the Key field.
> </modified text>

As I wrote above, I don't think "instruct" is enough here, or in
Section 6.15. Which fields are used, and how?

(As an example of ambiguity, the RSN IE can list multiple pairwise
cipher suites. If both TKIP and CCMP are listed in the RSN IE, what
does the WTP do? The IEEE 802.11 Station Session Key message
element could -- and perhaps should -- contain a "Cipher Suite" 
field, but currently, it doesn't.)

Best regards,
Pasi