code: func (p *PortAllocator) RequestPort(ip net.IP, proto string, port int) (int, error) {
  	return p.RequestPortInRange(ip, proto, port, port)
  }
docs: // RequestPort requests new port from global ports pool for specified ip and proto.
  // If port is 0 it returns first free port. Otherwise it checks port availability
  // in proto's pool and returns that port or error if port is already busy.