hi myself vicky,
in my office i have to block all messenger like yahoo messenger, windows live messenger, i have to block websites like www.yahoo.com, some more web sites. i need guidance through which i can accomplish this task
through ip tables or through squid server. i can use squid but i had heard that squid blocks pop and smtp also. squid creates some problem in receiving and sending email.

i am using red hat linux 4 box and installed squid having two ethernet card 1 is connected to adsl line and 2 is connected to switch. all clients will have proxy address of this linux box. guys need ur help ASAP.

Hey I'm sorry for past faulty reply.

If you say about pop and smtp, you need to make a smtp/pop relay server with sendmail/postfix/qmail whatever or u may use your ISP's one...

And you can set detailed acls in squid. Just go to squid.conf file and you'll have lot of acl formats, like time, port range etc. You can set em up. It's easy...

Not through iptables, unless you want future problems. Iptables works with ip addresses and you could use it to block by ip addresses but you have the problem that these change and that these can encompass multiple web sites.