sir,
i am working in rhel-5 and have two nic card and configured the router as follow

eth0-LAN(internal network having static ip)
eth1-external network(dhcp)

#iptables -I INPUT 1 -i lo -p all -j ACCEPT
#iptables -A FORWARD -i eth0 -j ACCEPT
#iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

After that i turn on the ip farward rule by following command

#sysctl -w net.ipv4.ip_forward=1
#echo 1 > /proc/sys/net/ipv4/ip_fprward
#service iptables save
#service iptables restart
#chkconfig -level 235 iptables on
#service iptables restart.
#service network restart

Now my router is working fine when ever i am pinging from my client pc(windows) i am getting the reply, and i am able to view the webpage also
but at a time only one network webpage is coming.if i am giving the address of dns server of external network in client pc than that network webpage is coming but to see our internal network webpage again i have to change the dns address in client pc.my all the client are in domain of internal network.

Is my router working fine,if not where i am wrong.please help me to solve this problem. so that just giving the address of webpage at URL page should resolute.Or i have to do some changes in client pc

if you are able to ping and browse web sites, i say router is routing. If you have to change DNS on client to resolve internal sites or external sites, then the problem is likely with DNS server forwarders and/or not having multiple DNS servers available for client to try. Typically, client will try DNS servers in order and wait timeout period before going to next one. If internal DNS server has forwarders, then client tries internal DNS and if internal DNS does not have answer it forwards to external DNS.


Hope this helps.