IPSec racoon/cisco problem

Hello.

on a linux machine (kernel 2.6.16.21) i installed ipsec-tools-0.6.5-10.6 to
create a VPN IPSec to a router CISCO.

System works fine but I have a problem. Through VPN a client reachs a web
server. Sometime, but not everytime, transfer of a 10Kbytes file requires
about 25/26 seconds (bandwidth is not a problem).

Same request, on local network requires few milliseconds. Through Internet
(without VPN) usually 3/400 milliseconds rarely max 1 or 2 seconds.

I believe the problem appear only on VPN requests.

Can be a racoon.conf mistake? Can you help me please?

Thank you.
Vittorio.