Subject: Re: IP compression of entire datagram

From: Avram Shacham <[email-masked]>
Date: Wed, 02 Sep 1998 17:43:26 -0700

Michael,

At 03:27 PM 9/2/98 +0000, Michael Giniger wrote:
>Hi
>
>I was reading through the IP compression draft and it appears that the
>draft only intends for IP compression to be performed on the payload
>portion of IP packets.  In the case of  IP security gateways that
>operate in tunnel mode, is it correct (and standards compliant) to
>perform IP compression on the entire inner IP datagram instead of just
>the payload portion of the inner IP datagram?

Right, IPComp is applied to the IP payload and in the case of a tunnel the payload does include the inner IP header.

Example #1:
     [IP2][IP1][TCP][data]
becomes
     [IP2][IPCOMP][IP1][TCP][data]
                           ****************** compressed
Example #2:
  [IP2]
    [ESP spi+replay+iv]
      [IPCOMP]
        [IP1]           ** compressed 
        [TCP]         ** compressed
        [data]         ** compressed
      [ESP padding+next protocol+auth]

This subject was discussed on both ipsec and ippcp mailing lists in the past (recently during 5-98), in case you are looking for more information.

Regards,
avram