My clients "can browse" outside but "can't ping" outside
 

Dear all,
I'm a newbie ...

My network config are :

Internet
I
Cable Modem
I
PIX Firewall
I
I I
I I
I I
Proxy Mail/Web
I
Clients

I used Mandrake 9.1 and the built in squid.
I had a problem with my network.
My Clients can browse Outside (The Internet), but My Clients cannot ping Outside.
Can anyone help me out from this problem ??

Squid is just a proxy server. It forwards port 80 (Web browsing) only. To make your machine act as a generic gateway machine (forwards all ports), you need to change the line

net.ipv4.ip_forward=0

to

net.ipv4.ip_forward=1

This will enable the gateway functionality. I will assume that you are using the kernel's built in firewalling software. To set up masquerading (makes all communications from clients appear to come from your machine) you need to add a line like

-t nat -A POSTROUTING -o eth1 -j SNAT --to 10.0.0.1

to /etc/iptables.conf. assuming that the cable modem is on interface eth1 and that eth1 has address 10.0.0.1. You will probably have to change these guesses to the correct values.