What is a external reliable IP address to ping to check if internet is available? [closed]

Try to ping 8.8.8.8, it's Google primary DNS server. I always ping it to verify my connection and I never found it down. Alternatively you can try 8.8.4.4, which is Google secondary DNS.

You can do what microsoft does: check that

http://www.msftncsi.com/ncsi.txt

returns "Microsoft NCSI". (This verifies that you can get the correct data from a site, e.g. not a Wifi portal or something else).

You can also check (e.g. ping) that dns.msftncsi.com

points to 131.107.255.255 (this verifies that DNS is working).

See http://technet.microsoft.com/en-us/library/ee126135

NB: You can also visit http://www.msftconnecttest.com/redirect to get yourself through a captive portal if needed.