vivek chal wrote:
> hello all
>
> i have made a server which is acting as a dhcp,dns and internet 
> gateway in scientific linux 4.5. Now i want my clients won't access 
> some websites such as orkut,facebook etc . Also i don't want to use 
> proxy. Please help me .
>

The best practice is to setup filtering with a transparent proxy or 
bridging firewall, there are other filtering mechanisms which require 
updating the filters often or manually. There are also custom LiveCDs, 
Wifi Hotspot Apps & Firewall Distro's that have all this built into a 
simple appliance distro which may be better suited for your application.

Setup a transparent proxy with Squid in three easy steps - 200712 NixCraft
http://www.cyberciti.biz/tips/linux-setup-transparent-proxy-squid-howto.html

How To Block WebPages Based On Keywords Or Phrases With SafeSquid Proxy 
Server
http://www.howtoforge.com/blocking-webpages-based-on-keywords-or-phrases-with-safesquid-proxy
http://www.howtoforge.com/how-to-enforce-google-safesearch-with-safesquid-proxy-server
http://www.howtoforge.com/how-to-block-porn-pictures-and-images-with-safesquid-proxy-server

How To Set Up Shorewall (Shoreline) 4.0 Firewall On CentOS 5.1
http://www.howtoforge.com/how-to-set-up-shorewall-firewall-on-centos-5.1

A parent's guide to Linux Web filtering - 200407 Linux.com
http://www.linux.com/articles/113733

DansGuardian
http://dansguardian.org/

-HTH Art@JAX