IPsec through NAT Mode

[Nilesh <niluforalways@yahoo.com>]

Hello All, 

I am using Squid proxy and IPtables. I am having some
problems to configure firewall. 
The problem is SNAT rule If I put rule in script I am
able to connect VPN server at outside world but could
not block yahoo messengers by squid without SNAT rule
I can block messenger through squid. 
I have checked VPN connection properties there is
check box IPsec through NAT mode . If I uncheck I wont
able to connect 
SNAT Rule 
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j SNAT --to
$EXTIP

could anyone help to solve my problem 
also I have tried this rules to connect VPN 
but wont work 
# IKE negotiations
$IPTABLES -A INPUT  -p udp --sport 500 --dport 500 -j
ACCEPT
$IPTABLES -A OUTPUT -p udp --sport 500 --dport 500 -j
ACCEPT
$IPTABLES -A FORWARD -p udp --sport 500 --dport 500 -j
ACCEPT
# ESP encrypton and authentication
$IPTABLES -A INPUT  -p 50 -j ACCEPT
$IPTABLES -A OUTPUT -p 50 -j ACCEPT
$IPTABLES -A FORWARD -p 50 -j ACCEPT
# uncomment for AH authentication header
#$IPTABLES -A INPUT  -p 51 -j ACCEPT
#$IPTABLES -A OUTPUT -p 51 -j ACCEPT



Thanks in advance 
Nilesh,




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