Re: Handling of IPcomp in IKEv2

[Avram Shacham <shacham@shacham.net>]

Radia,

The existing RFCs already specify a range of well-known compression
algorithms. (See the attached summary.)

Even with that option available, the vast majority of IPComp
implementations use the negotiated CPI (range 256-61439)  rather than the
well-known numbers. At least that was the status when the implementation
report,

  http://www.iesg.org/IESG/Implementations/IPCOMP-Implementation.txt ,

was written.

Regards,
avram


RFC-3173  IP Payload Compression Protocol

3.3.  IPComp Header Structure
[...]
   Compression Parameter Index (CPI)

      16-bit index.  The CPI is stored in network order.  The values
      0-63 designate 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  [..]  Note: When
      negotiating one of the well-known algorithms, the nodes MAY select
      a CPI in the pre-defined range 0-63.

RFC-2407  The Internet IP Security Domain of Interpretation for ISAKMP

4.4.5 IPSEC IPCOMP Transform Identifiers

   The IP Compression (IPCOMP) transforms define optional compression
   algorithms that can be negotiated to provide for IP payload
   compression ([IPCOMP]).  The following table lists the defined IPCOMP
   Transform Identifiers for the ISAKMP Proposal Payload within the
   IPSEC DOI.

       Transform ID                        Value
       ------------                        -----
       RESERVED                            0
       IPCOMP_OUI                          1
       IPCOMP_DEFLATE                      2
       IPCOMP_LZS                          3

and, RFC-3051 added
       IPCOMP_LZJH                         4



Radia Perlman - Boston Center for Networking wrote:
>[...]
> What you propose certainly sounds sane. Any chance of making
> it even simpler, and having the codes for identifying
> the compression algorithms be the same as the CPI? Then
> instead of saying, "I support xxx and will identify it with code 45",
you
> could just say "I support 45". I guess this would require
> IANA to assign a CPI before a compression algorithm could get
> used.
>
> Radia
>
>