Subject: [Capwap] Issue 189: Need better description of 'U' fields

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Tue, 16 Sep 2008 15:44:16 -0700

All,

Pasi identified the following issue as part of the WG Last Call:

    Section 4.6.1 ("Security" and "DTLS Policy" fields) and 4.6.42
    ("Frame Tunnel Mode" field): should probably say "Reserved and
    U: A set of..." (instead of having a separate text for 'U' bit
    that doesn't quite match the IANA considerations text anyway).

Pasi is right that the text for 'U' is not sufficient, and we need
to reuse the same text as what is currently used for the Reserved
field. That said, I would prefer to have a separate entry for the
'U' field (and probably rename it to 'R', for reserved). Therefore,
I am proposing the following:

<proposed text>
4.6.1.  AC Descriptor
[...]
   Security:   A 8 bit mask specifying the authentication credential
      type supported by the AC (See Section 2.4.4).  The field has the
      following format:

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |Reserved |S|X|R|
        +-+-+-+-+-+-+-+-+
      Reserved:  A set of reserved bits for future use.  All
         implementations complying with this protocol MUST set to zero
         any bits that are reserved in the version of the protocol
         supported by that implementation.  Receivers MUST ignore all
         bits not defined for the version of the protocol they support.

      S:   The AC supports the pre-shared secret authentication, as
         described in Section 12.6.

      X:   The AC supports X.509 Certificate authentication, as
         described in Section 12.7.

      R:   A reserved bit for future use.  All implementations complying
         with this protocol MUST set to zero any bits that are reserved
         in the version of the protocol supported by that
         implementation.  Receivers MUST ignore all bits not defined for
         the version of the protocol they support.
[...]
   DTLS Policy:   The AC communicates its policy on the use of DTLS for
      the CAPWAP data channel.  The AC MAY communicate more than one
      supported option, represented by the bit field below.  The WTP
      MUST abide by one of the options communicated by AC.  The field
      has the following format:

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |Reserved |D|C|R|
        +-+-+-+-+-+-+-+-+

      Reserved:  A set of reserved bits for future use.  All
         implementations complying with this protocol MUST set to zero
         any bits that are reserved in the version of the protocol
         supported by that implementation.  Receivers MUST ignore all
         bits not defined for the version of the protocol they support.

      D:   DTLS Enabled Data Channel Supported

      C:   Clear Text Data Channel Supported

      R:   A reserved bit for future use.  All implementations complying
         with this protocol MUST set to zero any bits that are reserved
         in the version of the protocol supported by that
         implementation.  Receivers MUST ignore all bits not defined for
         the version of the protocol they support.

4.6.42.  WTP Frame Tunnel Mode
[...]
      0
      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |Reservd|N|E|L|U|
     +-+-+-+-+-+-+-+-+

   Type:   41 for WTP Frame Tunnel Mode

   Length:   1

   Reservd:   A set of reserved bits for future use.  All
      implementations complying with this protocol MUST set to zero any
      bits that are reserved in the version of the protocol supported by
      that implementation.  Receivers MUST ignore all bits not defined
      for the version of the protocol they support.
[...]

   R:   A reserved bit for future use.  All implementations complying
      with this protocol MUST set to zero any bits that are reserved in
      the version of the protocol supported by that implementation.
      Receivers MUST ignore all bits not defined for the version of the
      protocol they support.
</proposed text>

PatC
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