diff --git a/pkg/apis/compute/vpcs_ovn.go b/pkg/apis/compute/vpcs_ovn.go
index cac44e9814..cf29532d10 100644
--- a/pkg/apis/compute/vpcs_ovn.go
+++ b/pkg/apis/compute/vpcs_ovn.go
@@ -18,6 +18,8 @@ import (
 	"yunion.io/x/pkg/util/netutils"
 )
 
+const VPC_OVN_ENCAP_COST = 58
+
 const (
 	VPC_EXTERNAL_ACCESS_MODE_DISTGW     = "distgw"     // distgw only
 	VPC_EXTERNAL_ACCESS_MODE_EIP_DISTGW = "eip-distgw" // eip when available, distgw otherwise
diff --git a/pkg/compute/models/guestnetworks.go b/pkg/compute/models/guestnetworks.go
index 89a86f4d99..445a5d7097 100644
--- a/pkg/compute/models/guestnetworks.go
+++ b/pkg/compute/models/guestnetworks.go
@@ -576,7 +576,7 @@ func (self *SGuestnetwork) getJsonDesc(network *SNetwork) *jsonutils.JSONDict {
 	desc.Add(jsonutils.NewString(self.Driver), "driver")
 	desc.Add(jsonutils.NewInt(int64(network.VlanId)), "vlan")
 	desc.Add(jsonutils.NewInt(int64(self.getBandwidth())), "bw")
-	desc.Add(jsonutils.NewInt(int64(self.getMtu())), "mtu")
+	desc.Add(jsonutils.NewInt(int64(self.getMtu(network))), "mtu")
 	desc.Add(jsonutils.NewInt(int64(self.Index)), "index")
 	vips := self.GetVirtualIPs()
 	if len(vips) > 0 {
@@ -812,15 +812,8 @@ func (self *SGuestnetwork) getBandwidth() int {
 	}
 }
 
-func (self *SGuestnetwork) getMtu() int {
-	net := self.GetNetwork()
-	if net != nil {
-		wire := net.GetWire()
-		if wire != nil {
-			return wire.Mtu
-		}
-	}
-	return options.Options.DefaultMtu
+func (self *SGuestnetwork) getMtu(net *SNetwork) int {
+	return net.getMtu()
 }
 
 func (self *SGuestnetwork) IsAllocated() bool {
diff --git a/pkg/compute/models/networks.go b/pkg/compute/models/networks.go
index 588b2a134e..cd493193cb 100644
--- a/pkg/compute/models/networks.go
+++ b/pkg/compute/models/networks.go
@@ -134,6 +134,21 @@ func (manager *SNetworkManager) AllowCreateItem(ctx context.Context, userCred mc
 	return db.IsAdminAllowCreate(userCred, manager)
 }
 
+func (self *SNetwork) getMtu() int {
+	baseMtu := options.Options.DefaultMtu
+
+	wire := self.GetWire()
+	if wire != nil {
+		baseMtu = wire.Mtu
+		if IsOneCloudVpcResource(wire) {
+			baseMtu -= api.VPC_OVN_ENCAP_COST
+		}
+		return baseMtu
+	}
+
+	return baseMtu
+}
+
 func (self *SNetwork) GetNetworkInterfaces() ([]SNetworkInterface, error) {
 	sq := NetworkinterfacenetworkManager.Query().SubQuery()
 	q := NetworkInterfaceManager.Query()
diff --git a/pkg/hostman/guestman/qemu-kvmhelper.go b/pkg/hostman/guestman/qemu-kvmhelper.go
index a264630f3f..8f2a75d613 100644
--- a/pkg/hostman/guestman/qemu-kvmhelper.go
+++ b/pkg/hostman/guestman/qemu-kvmhelper.go
@@ -277,6 +277,7 @@ func (s *SKVMGuestInstance) getNicAddr(index int) int {
 }
 
 func (s *SKVMGuestInstance) getVnicDesc(nic jsonutils.JSONObject) string {
+	bridge, _ := nic.GetString("bridge")
 	ifname, _ := nic.GetString("ifname")
 	driver, _ := nic.GetString("driver")
 	mac, _ := nic.GetString("mac")
@@ -295,6 +296,9 @@ func (s *SKVMGuestInstance) getVnicDesc(nic jsonutils.JSONObject) string {
 			cmd += fmt.Sprintf(",vectors=%d", vectors)
 		}
 		cmd += fmt.Sprintf("$(nic_speed %d)", bw)
+		if bridge == options.HostOptions.OvnIntegrationBridge {
+			cmd += fmt.Sprintf("$(nic_mtu %q)", bridge)
+		}
 	}
 	return cmd
 }
@@ -401,21 +405,32 @@ func (s *SKVMGuestInstance) _generateStartScript(data *jsonutils.JSONDict) (stri
 	// cmd += "    fi\n"
 	// cmd += "else\n"
 	cmd += "QEMU_CMD=$DEFAULT_QEMU_CMD\n"
-	// cmd += "fi\n"
-	cmd += "function nic_speed() {\n"
-	cmd += "    $QEMU_CMD "
-
 	if s.IsKvmSupport() {
-		cmd += "-enable-kvm"
+		cmd += "QEMU_CMD_KVM_ARG=-enable-kvm\n"
 	} else {
-		cmd += "-no-kvm"
+		cmd += "QEMU_CMD_KVM_ARG=-no-kvm\n"
 	}
+	// cmd += "fi\n"
+	cmd += `
+function nic_speed() {
+    $QEMU_CMD $QEMU_CMD_KVM_ARG -device virtio-net-pci,help 2>&1 | grep -q "\<speed="
+    if [ "$?" -eq "0" ]; then
+        echo ",speed=$1"
+    fi
+}
 
-	cmd += " -device virtio-net-pci,? 2>&1 | grep .speed= > /dev/null\n"
-	cmd += "    if [ \"$?\" -eq \"0\" ]; then\n"
-	cmd += "        echo \",speed=$1\"\n"
-	cmd += "    fi\n"
-	cmd += "}\n"
+function nic_mtu() {
+    local bridge="$1"; shift
+
+    $QEMU_CMD $QEMU_CMD_KVM_ARG -device virtio-net-pci,help 2>&1 | grep -q '\<host_mtu='
+    if [ "$?" -eq "0" ]; then
+        local origmtu="$(<"/sys/class/net/$bridge/mtu")"
+	if [ -n "$origmtu" -a "$origmtu" -gt 576 ]; then
+                echo ",host_mtu=$(($origmtu - 58))"
+	fi
+    fi
+}
+`
 
 	// Generate Start VM script
 	cmd += `CMD="$QEMU_CMD`
diff --git a/pkg/vpcagent/ovn/keeper.go b/pkg/vpcagent/ovn/keeper.go
index 01b86b5bb9..67d12efa09 100644
--- a/pkg/vpcagent/ovn/keeper.go
+++ b/pkg/vpcagent/ovn/keeper.go
@@ -296,7 +296,7 @@ func (keeper *OVNNorthboundKeeper) ClaimNetwork(ctx context.Context, network *ag
 		mdIp, "0.0.0.0",
 		"0.0.0.0/0", network.GuestGateway,
 	}
-	mtu -= 58
+	mtu -= apis.VPC_OVN_ENCAP_COST
 	const (
 		leaseTime  = 86400 * 365 * 3
 		renewTime  = 86400