Re: Handling of IPcomp in IKEv2

[Paul Koning <pkoning@equallogic.com>]

>>>>> "Henry" == Henry Spencer <henry@spsystems.net> writes:

 Henry> 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...

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

Speaking as one former implementer: I used CPI == 256 always, because
I didn't think I was allowed to pick a "well known" value on my own.
But the compression state was simply bundled with the IPsec state,
because for processing purposes you use all that stuff together.  So
the CPI was just 2 unnecessary bytes.

    paul