There might be many reasons for network not working as per our requirement. I am going to point out few things which I always do when there is some problem with network. And after working over all theses things for long time, I guess I will be covering most of the reasons for network not working as per our requirement.
Before you start, you can disable firewall using
#service iptables stop
1)You can use following command to configure your network adaptor
After that you can give it IP address, netmask, broadcast address or allow it to take ip from dhcp server. Then you can save and quit and give following command.
#service network restart
This is the command which you should use first to check if the network interfaces are as per your requirement. So this will confirm that network adaptor is enabled.
3)After this you can try connecting i.e. pinging some ip address in your network which is active. If ping does not work then mostly cable is not properly attached. You can use ethtool to figure that out.
If cable is fine then it will show at the bottom "Link detected : yes"
Otherwise it will show "no" instead of "yes". In that case you can try fixing the cable properly.
4) If there is still problem you can check further information about network card and just cross check it with following command.
#ethtool -i ethX
This will show information about network card
5)You can also check whether network card driver has loaded properly by using following command.
#lsmod | grep