Subject: [Capwap] Issue 172: How is the WTP Descriptor's Encryption Capabilities defined?

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Thu, 31 Jul 2008 10:12:23 -0700

Pasi's comment was:

   > Section 8.1: there probably should be IANA considerations text
about how the 
   > remaining bits are allocated.

The actual issue here is given the number of bits this field has (8),
are we 
expecting that a given WTP will advertise the encryption capabilities
based on 
the binding being advertised? This means that every binding spec would
be able 
to define all 8 bits. Of course, this would then create a potentially 
significant problem if a WTP advertises two separate bindings.

Currently, the new text in the binding specification is:
<new text>
8.1.  WTP Descriptor Message Element, Encryption Capabilities Field:

   This specification defines two new bits for the WTP Descriptor's
   Encryption Capabilities field, as defined in
   [I-D.ietf-capwap-protocol-specification].  Note that only the bits
   defined in this specification are described below.  The format of the
   Encryption Capabilities Field is:

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |       |A|T|   |
        +-+-+-+-+-+-+-+-+

   A:   WTP supports AES-CCMP, as defined in [IEEE.802-11.2007].

   T:   WTP supports TKIP and Michael, as defined in [IEEE.802-11.2007]
      and [WPA], respectively.
</new text>

Again, as currently specified, this means that bits 4 and 5 cannot be
redefined by another binding document. So we have to make a decision of
whether:
1. We allow the bits to be defined entirely by the binding
specification. Prevents a WTP from supporting two different bindings.
2. We allow the bits to be globally allocated. This allows a WTP to
advertise multiple bindings, but it restricts the encryption methods to
8 - for all bindings.
3. Create an interoperability issue by removing the encryption
capabilities field in the base document (or leave the field but mark it
reserved), and require all bindings to define their own encryption
capabilities message element.

Thoughts?

PatC
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