diff --git a/src/tuntap/tun.go b/src/tuntap/tun.go
index 6feb533b..1e994ea5 100644
--- a/src/tuntap/tun.go
+++ b/src/tuntap/tun.go
@@ -233,6 +233,12 @@ func (tun *TunAdapter) UpdateConfig(config *config.NodeConfig) {
 	// Replace the active configuration with the supplied one
 	tun.config.Replace(*config)
 
+	// If the MTU has changed in the TUN/TAP module then this is where we would
+	// tell the router so that updated session pings can be sent. However, we
+	// don't currently update the MTU of the adapter once it has been created so
+	// this doesn't actually happen in the real world yet.
+	//   tun.core.SetMaximumSessionMTU(...)
+
 	// Notify children about the configuration change
 	tun.Act(nil, tun.ckr.configure)
 }
diff --git a/src/yggdrasil/api.go b/src/yggdrasil/api.go
index e6b32e68..7f82c260 100644
--- a/src/yggdrasil/api.go
+++ b/src/yggdrasil/api.go
@@ -364,19 +364,23 @@ func (c *Core) SetNodeInfo(nodeinfo interface{}, nodeinfoprivacy bool) {
 }
 
 // GetMaximumSessionMTU returns the maximum allowed session MTU size.
-func (c *Core) GetMaximumSessionMTU(mtu uint16) uint16 {
-	mtu := 0
-	phony.Block(c.router, func() {
+func (c *Core) GetMaximumSessionMTU() uint16 {
+	var mtu uint16
+	phony.Block(&c.router, func() {
 		mtu = c.router.sessions.myMaximumMTU
 	})
 	return mtu
 }
 
 // SetMaximumSessionMTU sets the maximum allowed session MTU size. The default
-// value is 65535 bytes.
+// value is 65535 bytes. Session pings will be sent to update all open sessions
+// if the MTU has changed.
 func (c *Core) SetMaximumSessionMTU(mtu uint16) {
-	phony.Block(c.router, func() {
-		c.router.sessions.myMaximumMTU = mtu
+	phony.Block(&c.router, func() {
+		if c.router.sessions.myMaximumMTU != mtu {
+			c.router.sessions.myMaximumMTU = mtu
+			c.router.sessions.reconfigure()
+		}
 	})
 }
 
diff --git a/src/yggdrasil/session.go b/src/yggdrasil/session.go
index 78b0a3b2..c203fe2f 100644
--- a/src/yggdrasil/session.go
+++ b/src/yggdrasil/session.go
@@ -55,10 +55,6 @@ type sessionInfo struct {
 	callbacks     []chan func()       // Finished work from crypto workers
 }
 
-func (sinfo *sessionInfo) reconfigure() {
-	// This is where reconfiguration would go, if we had anything to do
-}
-
 // Represents a session ping/pong packet, andincludes information like public keys, a session handle, coords, a timestamp to prevent replays, and the tun/tap MTU.
 type sessionPing struct {
 	SendPermPub crypto.BoxPubKey // Sender's permanent key
@@ -138,9 +134,12 @@ func (ss *sessions) init(r *router) {
 }
 
 func (ss *sessions) reconfigure() {
-	for _, session := range ss.sinfos {
-		session.reconfigure()
-	}
+	ss.router.Act(nil, func() {
+		for _, session := range ss.sinfos {
+			session.myMTU = ss.myMaximumMTU
+			session.ping(ss.router)
+		}
+	})
 }
 
 // Determines whether the session with a given publickey is allowed based on