Merge pull request #13 from neilalexander/exchangemtu

Include endpoint MTU in session pings

src/yggdrasil/admin.go

@@ -223,6 +223,7 @@ func (a *admin) getData_getSessions() []admin_nodeInfo {
 			info := admin_nodeInfo{
 				{"IP", net.IP(sinfo.theirAddr[:]).String()},
 				{"coords", fmt.Sprint(sinfo.coords)},
+				{"MTU", fmt.Sprint(sinfo.getMTU())},
 			}
 			infos = append(infos, info)
 		}

src/yggdrasil/router.go

@@ -145,6 +145,10 @@ func (r *router) sendPacket(bs []byte) {
 		fallthrough
 	//default: go func() { sinfo.send<-bs }()
 	default:
+		if len(bs) > int(sinfo.getMTU()) {
+			// TODO: Send ICMPv6 Packet Too Big back to the TUN/TAP adapter
+			sinfo.core.log.Printf("Packet length %d exceeds session MTU %d", len(bs), sinfo.getMTU())
+		}
 		select {
 		case sinfo.send <- bs:
 		default:

src/yggdrasil/session.go

@@ -19,6 +19,8 @@ type sessionInfo struct {
 	myHandle     handle
 	theirNonce   boxNonce
 	myNonce      boxNonce
+	theirMTU     uint16
+	myMTU        uint16
 	time         time.Time // Time we last received a packet
 	coords       []byte    // coords of destination
 	packet       []byte    // a buffered packet, sent immediately on ping/pong
@@ -36,6 +38,7 @@ type sessionPing struct {
 	coords      []byte
 	tstamp      int64 // unix time, but the only real requirement is that it increases
 	isPong      bool
+	mtu         uint16
 }
 
 // Returns true if the session was updated, false otherwise
@@ -56,6 +59,9 @@ func (s *sessionInfo) update(p *sessionPing) bool {
 		s.theirNonce = boxNonce{}
 		s.nonceMask = 0
 	}
+	if p.mtu >= 1280 {
+		s.theirMTU = p.mtu
+	}
 	s.coords = append([]byte{}, p.coords...)
 	s.time = time.Now()
 	s.tstamp = p.tstamp
@@ -144,6 +150,8 @@ func (ss *sessions) createSession(theirPermKey *boxPubKey) *sessionInfo {
 	sinfo.mySesPub = *pub
 	sinfo.mySesPriv = *priv
 	sinfo.myNonce = *newBoxNonce()
+	sinfo.theirMTU = 1280
+	sinfo.myMTU = uint16(ss.core.tun.mtu)
 	higher := false
 	for idx := range ss.core.boxPub {
 		if ss.core.boxPub[idx] > sinfo.theirPermPub[idx] {
@@ -201,6 +209,7 @@ func (ss *sessions) getPing(sinfo *sessionInfo) sessionPing {
 		sendSesPub:  sinfo.mySesPub,
 		tstamp:      time.Now().Unix(),
 		coords:      coords,
+		mtu:         sinfo.myMTU,
 	}
 	sinfo.myNonce.update()
 	return ref
@@ -289,6 +298,13 @@ func (n *boxNonce) minus(m *boxNonce) int64 {
 	return diff
 }
 
+func (sinfo *sessionInfo) getMTU() uint16 {
+	if sinfo.theirMTU < sinfo.myMTU {
+		return sinfo.theirMTU
+	}
+	return sinfo.myMTU
+}
+
 func (sinfo *sessionInfo) nonceIsOK(theirNonce *boxNonce) bool {
 	// The bitmask is to allow for some non-duplicate out-of-order packets
 	diff := theirNonce.minus(&sinfo.theirNonce)

src/yggdrasil/wire.go

@@ -429,12 +429,14 @@ func (p *sessionPing) encode() []byte {
 	bs = append(bs, wire_encode_uint64(wire_intToUint(p.tstamp))...)
 	coords := wire_encode_coords(p.coords)
 	bs = append(bs, coords...)
+	bs = append(bs, wire_encode_uint64(uint64(p.mtu))...)
 	return bs
 }
 
 func (p *sessionPing) decode(bs []byte) bool {
 	var pType uint64
 	var tstamp uint64
+	var mtu uint64
 	switch {
 	case !wire_chop_uint64(&pType, &bs):
 		return false
@@ -449,11 +451,14 @@ func (p *sessionPing) decode(bs []byte) bool {
 		return false
 	case !wire_chop_coords(&p.coords, &bs):
 		return false
+	case !wire_chop_uint64(&mtu, &bs):
+		mtu = 1280
 	}
 	p.tstamp = wire_intFromUint(tstamp)
 	if pType == wire_SessionPong {
 		p.isPong = true
 	}
+	p.mtu = uint16(mtu)
 	return true
 }
 

yggdrasil.go

@@ -40,6 +40,7 @@ type nodeConfig struct {
 	LinkLocal   string
 	IfName      string
 	IfTAPMode   bool
+	IfMTU       int
 }
 
 type node struct {
@@ -114,6 +115,7 @@ func generateConfig() *nodeConfig {
 	cfg.Multicast = true
 	cfg.LinkLocal = ""
 	cfg.IfName = "auto"
+	cfg.IfMTU = 65535
 	if runtime.GOOS == "windows" {
 		cfg.IfTAPMode = true
 	} else {
@@ -264,7 +266,7 @@ func main() {
 	n.init(cfg, logger)
 	logger.Println("Starting tun...")
 	//n.core.DEBUG_startTun(cfg.IfName) // 1280, the smallest supported MTU
-	n.core.DEBUG_startTunWithMTU(cfg.IfName, cfg.IfTAPMode, 65535) // Largest supported MTU
+	n.core.DEBUG_startTunWithMTU(cfg.IfName, cfg.IfTAPMode, cfg.IfMTU) // Largest supported MTU
 	defer func() {
 		logger.Println("Closing...")
 		n.core.DEBUG_stopTun()