Lots of times you need to determine your public IP address, if you are using Linux operating system to power your PC, you may use some good console commands to guess your public IP address.
Most of these methods will return you the local IP and not the public IP of your proxy if you are behind one.
dig +short myip.opendns.com @resolver1.opendns.com
Will return public IP.
wget -q -O - checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$//'
That will return your local IP.
That is going to return you the public IP you are using to access internet. If you are behind a NAT or proxy, it will the IP of that proxy.