I'm running CentOS-6 on an HP MicroServer with a Billion 5200S modem/router connecting to the internet. I'm running the standard CentOS-6 firewall on the server.
(1) I can open port 22 on the Billion, allowing me to ssh in from outside. But for some reason I cannot ping the same address from outside. (I can ping it internally.) Why is this? I'm not sure if the problem lies with the router or the server? There does not seem to be any explicit rule on either to allow ICMP packets through.
(2) I have a Linksys WRT54GL WiFi router attached to the server, to allow access to the internet from laptops. This works fine. But I was surprised to find that when I turn OFF the firewall on the server this stops access to the internet on laptops. (I didn't test to see if re-booting the laptop would solve this.) Can disabling the firewall actually prevent some linkage?