Subject: [Capwap] Data Tunneling Header

From: Jim Murphy <[email-masked]>
Date: Thu, 13 Apr 2006 10:21:24 -0700

I would like to propose the following Data Tunnel header for CAPWAP
to address the following issues with the existing header:

1. It includes RF information that is 802.11 specific.
    CAPWAP goals are that the protocol be extensible to
    arbitrary wireless protocols.

2. The RID is 3 bits but elsewhere in the document it is 8 bits.
    The RID is also RF specific information which should be in the RF
    specific part.

3. The Length field is redundant with the UDP header's length field.

4. It does not specify the payload type.

The following header is proposed to overcome these issues. This header
includes three parts, the base header, the security header and the
RF header. The base header is defined as follows:

[NOTE: I am not sure that the security header is of any use, I am
  including it to solicit comments.]

Base tunnel header:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |VER|  HLEN |S|R|    TYPE       |   RESV    |F|L|    Frag ID    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

VER: Same as CAPWAP-00

HLEN: Length of CAPWAP tunnel header in 4 byte words. (Similar to IP
       header length). The maximum total header size is therefore
       15*4 = 60 bytes. This length includes the optional security
       header and RF headers.

S: Security bit. If set the tunnel header includes a security
    encapsulation. The security encapsulation follows
    immediately after the base CAPWAP tunnel header. If not set, there
    is no security header. The security header must be padded to a 4
    byte boundary.

R: RF bit. If set, the tunnel header includes RF information. The RF
    information in the tunnel header follows immediately after the
    security header. If no security header exists, the RF information
    follows immediately after the base tunnel header.

TYPE: This is the payload type. The following types are defined:

       0x00 Reserved
       0x01 802.3
       0x02 802.11
       0x03 - 0xFF Reserved

RESV: Reserved bits.

F, L, Frag ID - Same as CAPWAP-00.

Security Tunnel Header:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | SHLEN |             TBD                                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

SHLEN: Length of security header

RF tunnel header:

The RF tunnel header includes payload type specific RF information.
It is defined specifically for each payload type. It must include its
length if units of 4 bytes in the first nibble as follows:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | RHLEN |             TBD                                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

RHLEN: Length of the RF tunnel header.

[NOTE: If there is no security header, there is no need for a RHLEN
  field.]

Method of operation:

When a switch receives a packet it check the version.
If VER == 0 continue; else drop
If S == 1 decrypt
If R == 1 do RF processing
If TYPE == 1, deencap HLEN * 4 bytes and 802.3 switch.
If TYPE == 2, deencap HLEN * 4 bytes and 802.11 switch.

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