NAT-PMP is the direct concurrent to the UPnP IGD specification. It
is providing a way to do NAT traversal. libnatpmp is an attempt to
make a portable and fully compliant implementation of the protocol for
the client side. It is based on non blocking sockets and all calls of
the API are asynchronous. It is therefore very easy to integrate the
NAT-PMP code to any event driven code.