Testing and Troubleshooting

You can test to see whether the new NIC is operational (at least the kernel module) by pinging its IP address (for example):

 #ping 10.1.1.1 

(Press CTRL-C to break out of this listing and see a summary report of your ping statistics. It should indicate "0% packet loss," if everything is working properly.)

If it does not work, you will see:

 10.1.1.1: Destination Host Unreachable 

(Press CTRL-C to break out of this listing as well.)

The first step in troubleshooting this new NIC (after you have made sure the network cable is connected) is to enter the command:

 #ifconfig -a | more 

Make sure your new eth device has been added to this listing and contains the following line:

 UP BROADCAST RUNNING MULTICAST MTU:nnnn Metric:n 

(Where n indicates a number.)

If you do not see the word UP at the beginning of this line, it means your ifup command did not work properly. You will need to go back and make sure you have the correct eth device and network driver (either compiled into the kernel or compiled as a module in the /lib/modules directory).

If you do see the word UP, try pinging the IP address of this eth device (the local IP address on your machine) which in this example would be the following command:

 #ping 10.1.1.2 

If this does not report 0% packet loss when you press CTRL-C, it probably means you have made a mistake in the above steps and need to go back and check everything you have entered again.

If this works, however, it means there is still something blocking your packets from getting to the destination host and back (Internet Control Message Protocol or ICMP packets, to be precise).

Make sure you do not have any ipchains or iptables rules that would block communication between your system and another host. You can remove all ipchains or iptables rules with the -F (flush) option:

 #ipchains -F or #iptables -F 

List the rules with the -L option:

 #ipchains -L or #iptables -L 

Your input, forward, and output default policy should now be ACCEPT. (Of course, make sure the host you are trying to ping is not blocked by an intervening firewall and that it is also not using iptables/ipchains rules to block your ICMP ping packets.) See Chapter 2 for more information on how to configure the ipchains and iptables rules properly.

Note 

If the ping command now works, you may need to modify your ipchains rules in the file /etc/sysconfig/ipchains or /etc/sysconfig/iptables.

If the ping command still does not work, you might try using another method of communicating with the remote host (try to telnet to it). If this works, it probably means a firewall between your systems is blocking ICMP traffic.

See the online manual, "Linux Network Administrators Guide," for more information about configuring and enabling NICs on your Linux system.