change in draft-ietf-ippcp-protocol-06.txt

[Avram Shacham <[e-mail]>]

The change in <draft-ietf-ippcp-protocol-06.txt>, which was announced
today, is documenting the discussions on the mailing-list during the past
few weeks. 

The change is simple:  It reserve the CPI range 64-255 for future use, so
negotiated CPIs must - for now - be in the range 256-61439, instead of
64-61439 as in the previous versions of the protocol.

The reason - the ISAKMP field for negotiating IPCOMP Transform Identifiers
is of 8-bit, i.e. providing the range 0-255.  The IPPCP wg decided to
dedicate the  values 1-63 to well-known algorithms (and this decision
stays)  and to start the negotiated CPIs at 64.  Following this path, it
will be hard in the future to reclaim the range 64-255 for Transform IDs,
as it may break existing implementations.   To enable such future
expansion, the protocol gives up 192 CPI values out of 61376 (about
0.313%.)  In the future, probably before moving IPComp to Standard, the wg
may decide to use this range for well-known algorithms or to add the range
to the negotiated CPIs. 

As diff shows, the actual change is in the definition of CPI - see lines
marked ** on the right:

3.3.  IPComp Header Structure

Compression Parameter Index (CPI)

=== previous version ===
 
     16-bit index.  The CPI is stored in network order.  The values
     0-63 define well-known compression algorithms, which require no
     additional information, and are used for manual setup.  The
     values themselves are identical to IPCOMP Transform identifiers
     as defined in [SECDOI].  Consult [SECDOI] for an initial set of
     defined values and for instructions on how to assign new values.

     The values 64-61439 are negotiated between the two nodes in     **
     definition of an IPComp Association, as defined in section 4.   ** 
     Note:  When negotiating one of the well-known algorithms, the
     nodes MAY select a CPI in the pre-defined range 0-63.  The
     values 61440-65535 are for private use among mutually consenting
     parties.

=== new version ===

     16-bit index.  The CPI is stored in network order.  The values
     0-63 define well-known compression algorithms, which require no
     additional information, and are used for manual setup.  The
     values themselves are identical to IPCOMP Transform identifiers
     as defined in [SECDOI].  Consult [SECDOI] for an initial set of
     defined values and for instructions on how to assign new values.
     The values 64-255 are reserved for future use.  The values 256-  **
     61439 are negotiated between the two nodes in definition of an   **
     IPComp Association, as defined in section 4.  Note:  When        **
     negotiating one of the well-known algorithms, the nodes MAY      
     select a CPI in the pre-defined range 0-63.  The values 61440-
     65535 are for private use among mutually consenting parties.

Regards,
avram