Re: Handling of IPcomp in IKEv2

[Henry Spencer <henry@spsystems.net>]

On Sun, 8 Dec 2002, Avram Shacham wrote:
> Even with that option available, the vast majority of IPComp
> implementations use the negotiated CPI (range 256-61439)  rather than the
> well-known numbers...

Most of the motive for this, I think, is that it's convenient to have a
local object to hold state for compression -- the compression proper is
usually stateless, but choice of algorithm, intelligent decision on
whether to attempt compression, etc. require local state -- and negotiated
CPIs let you give that state a number (although not very conveniently so,
since the decompressor picks the CPI but it's the compressor that wants to
keep state). 

I don't think any significant amount of the negotiation is being done to
permit custom compression algorithms.

                                                          Henry Spencer
                                                       henry@spsystems.net