diff --git a/router/fastdp.go b/router/fastdp.go
index 6a867f9d..d0c5a43f 100644
--- a/router/fastdp.go
+++ b/router/fastdp.go
@@ -32,7 +32,7 @@ type FastDatapath struct {
 	lock             sync.Mutex // guards state and synchronises use of dpif
 	dpif             *odp.Dpif
 	dp               odp.DatapathHandle
-	mtu              int // [1]
+	iface            *net.Interface
 	deleteFlowsCount uint64
 	missCount        uint64
 	missHandlers     map[odp.VportID]missHandler
@@ -59,10 +59,6 @@ type FastDatapath struct {
 
 	// forwarders by remote peer
 	forwarders map[mesh.PeerName]*fastDatapathForwarder
-
-	// [1] The mtu from the datapath netdev (which should match the
-	// mtus on all the veths hooked up to the datapath).  We validate
-	// that we are able to support that mtu.
 }
 
 func NewFastDatapath(dpName string, port int) (*FastDatapath, error) {
@@ -92,7 +88,7 @@ func NewFastDatapath(dpName string, port int) (*FastDatapath, error) {
 		dpname:        dpName,
 		dpif:          dpif,
 		dp:            dp,
-		mtu:           iface.MTU,
+		iface:         iface,
 		missHandlers:  make(map[odp.VportID]missHandler),
 		sendToPort:    nil,
 		sendToMAC:     make(map[MAC]bridgeSender),
@@ -665,7 +661,7 @@ func (fwd *fastDatapathForwarder) sendHeartbeat() {
 
 	// the heartbeat payload consists of the 64-bit connection uid
 	// followed by the 16-bit packet size.
-	buf := make([]byte, EthernetOverhead+fwd.fastdp.mtu)
+	buf := make([]byte, EthernetOverhead+fwd.fastdp.iface.MTU)
 	binary.BigEndian.PutUint64(buf[EthernetOverhead:], fwd.connUID)
 	binary.BigEndian.PutUint16(buf[EthernetOverhead+8:], uint16(len(buf)))