Can't ping

Introduction:

I must confess, I had all sorts of problems with network connectivity once I came to test my NIC configuration, and this was partly my own fault. As a software engineer, I always assume that any problems I have are in software - especially right after a complex software installation or change. So, when I couldn't ping my PC from the server and vice versa, I went on a long fruitless search through my configuration. It took a post here to put me right (oh, and BTW, you should favorite that link right now).

This, then, is a diagnostic and fix for one possible problem that will not let you ping from your LInux box to your Windoze box and vice versa.

Aim:

Diagnose and fix a network problem where ping does not work.

Requirements:

You have got to this stage of your installation and the ping test has failed.

Procedure:

Diagnose:

• Log in as root.
• Open Terminal.
• # ifconfig
• You should get a result something like this:
  

# ifconfig eth0 Link encap:Ethernet HWaddr 00:0D:88:32:06:4A inet addr:192.168.0.2 Bcast:192.168.0.255 Mask:255.255.255.0 inet6 addr: fe80::20d:88ff:fe32:64a/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:27 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 b) TX bytes:2240 (2.1 KiB) Interrupt:10 Base address:0xe800 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:1382 errors:0 dropped:0 overruns:0 frame:0 TX packets:1382 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1800890 (1.7 MiB) TX bytes:1800890 (1.7 MiB) #

• Look at the 4th line in the 'eth0' section. You should see the 'RUNNING' flag there. If you don't there is a hardware problem because that flag is only present when the network card sees a good connection.
• However, it is possible that you still have a hardware problem even when the 'RUNNING' flag is present. This is when you are plugged into a hub and there is either a problem with the hub or the other cable going into it.The hub tries to look, electrically, like a network card to the incomming cable. It may fool ifconfig into thinking that it has a good connection.
• The best thing to do here is disconnect the cables from both network cards and connect them together directly with a crossover cable. One you KNOW to be good. If you can ping with this carrying the connection, the problem is either with your hub or one of the cables.

Fix:

• Try reconnecting with normal CAT5 cables that you absolutely know to be good or change the hub.