Just include the IP address part, and not the port number (the bit after the colon), i.e. as I wrote it in my post.
Don't turn off the firewall yet
Edit: I should have said more clearly, the command:
> ping -n 10 126.96.36.199
..is in three parts, (1) the 'ping' command, i.e. the program to run, the (2) the '-n 10' part, to say 'do this 10 times' as the default is 3 and you might miss a dropped packet and (3) the IP4 address of the ATAG server, which is 188.8.131.52 (I think, I didn't double check for real).