Hi all,
I have four internet lines through which office users access the internet. Now i want to implement a firewalled gateway so that internet traffic goes through a firewall so that i can filter contents accessed by users. I have successfully tested it using iptables and squid service for single internet line. Problem is that how to integrate four internet lines for the same task. Please help me regarding this as it is very urgent.

4 lines, same computer Squid server? It all depends on how those four lines are actually set up.

Are they bonded into one virtual connection? If they are not, can they be? Can they be? What's the network topology of the office users? How many people will be accessing the websites? What kind of connections are these? Modem? DSL? T1? OC45?

If you're trying to distribute each website request across all four connections simultaneously, you might do some searching for load balancing solutions.

But based on the scant information you've provided, I cannot give answers, only questions.

Four lines means DSL lines they are not bonded into any virtual connection how can i bond them? And yes you got it i want to load balance the internet traffic into four lines... as well as filter them . Yes same server is running squid. Current situation is that users directly using the internet through DSL lines i have to implement the Linux Firewall as well as Bandwidth management solution to office .

Bonding has to be done with the knowledge and support of your ISP.

You'll either set up 4 firewalls and internal networks/routing paths, or use some kind of load-balancing/NAT setup. It can probably be done with iptables if you understand it at the guru level, but it's not an easy road to travel.

I wish you luck.