RE: "Deprecate"

["Templin, Fred L" <[e-mail]>]

Hi,

Up to now, the SEAL spec has focused on "tunnel mode", and had the
singular statement:

  "(A transport-mode of operation is also possible, but out of scope
   for this document.)"

in the introduction. (Indeed, the first edition of SEAL (RFC5320)
did specify a transport mode of operation, but that document will
be obsolete by the second edition.) So, in light of these discussions
I decided that now might be a good time to bring transport mode back
into scope and as such have added the following new section to the
document. Please send comments and suggestions. I will post a new
draft version by the end of the day that will include both tunnel
and transport modes.

Thanks - Fred
[e-mail]

6.  SEAL Transport Mode Specification

   SEAL is also used for transport-mode operation.  Transport mode
   refers to a SEAL encapsulation in which a layer-4 header appears
   immediately following the SEAL header.  The type of layer-4 header is
   indicated in the "NEXTHDR" field the same as for tunnel mode.  The
   SEAL header is identical to the version used for tunnel mode, except
   that the "LINK_ID" and "LEVEL" fields are omitted, and the transport
   layer port numbers are included in each non-initial segment (see:
   Figure 6).

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    NEXTHDR    |VER|C|P|I|V|R|M|     Offset    |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Source Port (when Offset!=0)  |   Dest Port (when Offset!=0)  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Identification (optional)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Integrity Check Vector (optional)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   ...

                       Figure 6: SEAL Header Format

   The "Source Port" and "Dest Port" are taken from the corresponding
   fields in the transport layer next header that appears immediately
   following the SEAL header in the initial segment.  For example, for
   UDP [RFC0768] the transport layer source/dest ports are 16 bits in
   length and are copied from the transport layer header.  All
   segmentation is exactly as specified in SEAL tunnel mode, and the
   SEAL Control Message Protocol (SCMP) operates the same as for tunnel
   mode.  For example, the source node can probe the path MTU to the
   destination by setting the P bit in a probe packet and waiting for an
   acknowledgement from the destination.

   SEAL transport mode is useful for transport layer protocols that have
   no way to segment the large packets they send.  It is a universal
   format that can be applied to any such transport.