Add LinkLocalTCPPort option

src/config/config.go

@@ -22,6 +22,7 @@ type NodeConfig struct {
 	SigningPublicKey            string                 `comment:"Your public signing key. You should not ordinarily need to share\nthis with anyone."`
 	SigningPrivateKey           string                 `comment:"Your private signing key. DO NOT share this with anyone!"`
 	MulticastInterfaces         []string               `comment:"Regular expressions for which interfaces multicast peer discovery\nshould be enabled on. If none specified, multicast peer discovery is\ndisabled. The default value is .* which uses all interfaces."`
+	LinkLocalTCPPort            uint16                 `comment:"The port number to be used for the link-local TCP listeners for the\nconfigured MulticastInterfaces. This option does not affect listeners\nspecified in the Listen option. Unless you plan to firewall link-local\ntraffic, it is best to leave this as the default value of 0."`
 	IfName                      string                 `comment:"Local network interface name for TUN/TAP adapter, or \"auto\" to select\nan interface automatically, or \"none\" to run without TUN/TAP."`
 	IfTAPMode                   bool                   `comment:"Set local network interface to TAP mode rather than TUN mode if\nsupported by your platform - option will be ignored if not."`
 	IfMTU                       int                    `comment:"Maximux Transmission Unit (MTU) size for your local TUN/TAP interface.\nDefault is the largest supported size for your platform. The lowest\npossible value is 1280."`

src/yggdrasil/multicast.go

@@ -16,12 +16,16 @@ type multicast struct {
 	sock        *ipv6.PacketConn
 	groupAddr   string
 	listeners   map[string]*tcpListener
+	listenPort  uint16
 }
 
 func (m *multicast) init(core *Core) {
 	m.core = core
 	m.reconfigure = make(chan chan error, 1)
 	m.listeners = make(map[string]*tcpListener)
+	m.core.configMutex.RLock()
+	m.listenPort = m.core.config.LinkLocalTCPPort
+	m.core.configMutex.RUnlock()
 	go func() {
 		for {
 			e := <-m.reconfigure
@@ -148,12 +152,14 @@ func (m *multicast) announce() {
 				var listener *tcpListener
 				if l, ok := m.listeners[iface.Name]; !ok || l.listener == nil {
 					// No listener was found - let's create one
-					listenaddr := fmt.Sprintf("[%s%%%s]:0", addrIP, iface.Name)
+					listenaddr := fmt.Sprintf("[%s%%%s]:%d", addrIP, iface.Name, m.listenPort)
 					if li, err := m.core.link.tcp.listen(listenaddr); err == nil {
 						m.core.log.Debugln("Started multicasting on", iface.Name)
 						// Store the listener so that we can stop it later if needed
 						m.listeners[iface.Name] = li
 						listener = li
+					} else {
+						m.core.log.Warnln("Not multicasting on", iface.Name, "due to error:", err)
 					}
 				} else {
 					// An existing listener was found