I'm behind a router with my other computer. When I try pinging my external IP or the host resolving to it, I don't get host unreachable or a timeout, there just isn't any output at all. It looks like this:
username@username:~$ ping X.X.X.X PING X.X.X.X (X.X.X.X) 56(84) bytes of data.
I'm able to ping any computer in my LAN, my default gateway, the broadcast and any alive host from the WWW. My internal LAN Card is Atheros GbE LAN chip.
So far I have tried and understood the following:
I'm using Xubuntu 13.04 Raring and my PC has a dual boot with it and Windows 7. In Windows I don't face such problems, everything seems OK, so it's not my router or computer.
In Linux I use one single iptables rule for protecting a server I'm running and nothing else, so it's not a firewall issue.
I connected my laptop to my neighbour's Wi-Fi (same ISP, different router brands) and booted a Live USB with my current OS (Xubuntu 13.04) - everything worked, pings to the external IP were successful.
Enabled my own Wi-Fi and connected to it with the laptop (same OS). Tried pinging the IP and the host resolving to it and it worked - another confirmation that it isn't a router problem.
Tried fping on my PC and it shows "X.X.X.X is unreachable" (where X.X.X.X is my external IP).
My other PC uses Windows XP and pings are successful there.
I connected an external PCI LAN card (Realtek) to my PC and tried pinging in both OS and Live USB and it was unsuccessful.
Can somebody please explain what the problem might be and suggest a solution? Thanks in advance.
To address the question's gertvdijk asked:
Well, DMZ from NAT is activated for my PC's LAN address in the router's settings and some ports (27000-27050) are forwarded. Even if the NAT Loopback is the solution, my 'hi-tech' router doesn't have such a feature. I'm going to try to enable DMZ for the laptop's IP and try to ping my external IP from the Live USB. I'm also going to try with Ubuntu 10.10 Live CD later and will post the outcome...
By the way, I have a Canyon CNP-WF514 and as far as I remember when I had Canyon CNP-BR1 this wasn't an issue. I'm not entirely sure about the pinging but back then I was able to connect to my server from my external IP and now I'm not (only from my local one).