["J. Holmes" <iamholmes@xxxxxxxxx>]

Hi all -

         Firstly, this isn't an Ethereal question per se. Its an observation I made 
when using Ethereal. However, I'm certain that there are some networking
protocol gurus (Guy and co.) that can explain some of these questions.

 I have a simple setup with two boxes that do IPCOMP 
compression connected as in th ASCII diagram below :

   LAN a -- CPR --- router --(simulated WAN)--- router -- hub -- CPR -- LAN b

I did an FTP transfer from a PC in LAN a to a PC in Lan b. Now when I sniffed the 
IPCOMP pkts using Ethereal, I found that the source and destination IP addresses
had changed to the local and remote IPCOMP compression units' IP addresses
respectively.

I'm confused. 

1. How does the remote IPCOMP compression unit know whom to send
    the pkts to ? (Given that the dest. IP address is the remote IPCOMP
    decompressor, and not the original destination -- the FTP server/client).
2. The RFC doesn't indicate that the source or destination IP address should
    be changed. What am I not understanding here ?
3. The header for the IPCOMP includes the protocol field from the IP header. 
    Why would you have the protocol field from the IP header. This part of the IP
    header is left intact, and not compressed. Isn't this redundant ?

Many thanks for any replies.

J.