Check if this machine has a public IP address.

It checks all the network interfaces for IPv4 public addresses and returns true if one address is found.

	function OnGUI() {
		if (GUILayout.Button ("Start Server")) {
			// Use NAT punchthrough if no public IP present
			var useNat = !Network.HavePublicAddress();
			Network.InitializeServer(32, 25002, useNat);
			MasterServer.RegisterHost("MyUniqueGameType", 
				"JohnDoes game", "l33t game for all");
		}
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnGUI() {
        if (GUILayout.Button("Start Server")) {
            bool useNat = !Network.HavePublicAddress();
            Network.InitializeServer(32, 25002, useNat);
            MasterServer.RegisterHost("MyUniqueGameType", "JohnDoes game", "l33t game for all");
        }
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnGUI() as void:
		if GUILayout.Button('Start Server'):
			useNat as bool = (not Network.HavePublicAddress())
			Network.InitializeServer(32, 25002, useNat)
			MasterServer.RegisterHost('MyUniqueGameType', 'JohnDoes game', 'l33t game for all')