Local Client's External Address
The client uses public web services which return the information to determine its own external, routable IP address.
The client runs a thread called ThreadGetMyExternalIP (in net.cpp) which attempts to determine the client's IP address as seen from the outside world.
First, it attempts to connect to 91.198.22.70 port 80, which should be the checkip.dyndns.org server. If connection fails, a DNS request is made for checkip.dyndns.org and a connection is attempted to that address. Next, it attempts to connect to 74.208.43.192 port 80, which should be the www.showmyip.com server. If connection fails, a DNS request is made for www.showmyip.com and a connection is attempted to that address.
For each address attempted above, the client attempts to connect, send a HTTP request, read the appropriate response line, and parse the IP address from it. If this succeeds, the IP address is returned, it is advertised to any connected nodes, and then the thread finishes (without proceeding to the next address).