[lug] How does ping work? How to diagnose firewall problem?

[siegfried]

I went to a friend's house and thought I opened up port 22 and 1194 on his
router. Since he does not have a fixed IP address, I went to
http://www.grc.com/x/ne.dll?rh1dkyd2 and wrote down the IP address while it
did a port scan on us. 

Unfortunately, the port scan stopped at 1056 and I never could verify that
port 1194 was open. 

So now I am home and I'm trying to ping his IP address. I suppose I could
have become very unlucky and he got a new IP address from his DHCP server
while I was driving home.

What is required for ping to work? Does it need a port open? Which port?

Thanks,
Siegfried