How do I make a direct connection between two computers via ethernet?
 

I hooked up an ethernet cable between two computers. I brought up the interfaces, assigned ip addresses and inputed the hostname and MAC address of each by using the arp command. Now, when I try pinging each other, I get an icmp host unreachable message. Both computers' /proc/sys/net/ipv4/icmp_echo_ignore_all is set to 0.

I don't recall all the details, but it seems you know most of them.

You don't mention if you used a crossover cable. This is required for what you are doing---it reverses some of the connections.

Need a crossover cable or adapter to connect 2 computers.

hmm I thought that all you would need to do is connect like you would a server, I turned an old computer into a hardware firewall using smoothwall and I connect to it using my web browser

If you connect both PCs to a hub or router, then you could use a normal ethernet cable, however direct connections require a cross-over cable.

Ah I c, thanks guys.

hmm I don't understand that because how is it that the only thing connecting me to my hardware firewall ( which is actually an old PC using smoothwall) is an ethernet cable and I communicate all the time between the two I don't use a hub or router?

Some modern networks cards and hubs are capable of working out if they need a crossover and will automatically do that for you

older cards and hubs will not

in general if you are connecting 2 of the same together you use a X-over and a patch if its one of each.