optimize(mtu): Set lowest MTU among bound interfaces to dae0/dae0peer

common/netutils/dns.go

@@ -15,7 +15,6 @@ import (
 	"sync"
 	"time"
 
-	"github.com/daeuniverse/dae/common/consts"
 	"github.com/daeuniverse/outbound/netproxy"
 	"github.com/daeuniverse/outbound/pkg/fastrand"
 	"github.com/daeuniverse/outbound/pool"
@@ -255,7 +254,7 @@ func resolve(ctx context.Context, d netproxy.Dialer, dns netip.AddrPort, host st
 		}()
 	}
 	go func() {
-		buf := pool.GetFullCap(consts.EthernetMtu)
+		buf := pool.GetFullCap(GetEthernetMtu())
 		defer buf.Put()
 		if magicNetwork.Network == "tcp" {
 			// Read DNS response length

common/netutils/mtu.go

@@ -0,0 +1,27 @@
+/*
+*  SPDX-License-Identifier: AGPL-3.0-only
+*  Copyright (c) 2022-2025, daeuniverse Organization <dae@v2raya.org>
+ */
+
+package netutils
+
+import "sync"
+
+var (
+	ethernetMtu = 9000
+	mtuMux      sync.RWMutex
+)
+
+func UpdateEthernetMtu(mtu int) {
+	mtuMux.Lock()
+	defer mtuMux.Unlock()
+	if mtu < ethernetMtu {
+		ethernetMtu = mtu
+	}
+}
+
+func GetEthernetMtu() int {
+	mtuMux.RLock()
+	defer mtuMux.RUnlock()
+	return ethernetMtu
+}

control/control_plane.go

@@ -42,6 +42,7 @@ import (
 	dnsmessage "github.com/miekg/dns"
 	"github.com/mohae/deepcopy"
 	"github.com/sirupsen/logrus"
+	"github.com/vishvananda/netlink"
 	"golang.org/x/sys/unix"
 )
 
@@ -142,6 +143,14 @@ func NewControlPlane(
 		return nil, err
 	}
 
+	for _, ifname := range append(global.LanInterface, global.WanInterface...) {
+		link, err := netlink.LinkByName(ifname)
+		if err != nil {
+			return nil, err
+		}
+		netutils.UpdateEthernetMtu(link.Attrs().MTU)
+	}
+
 	if err = GetDaeNetns().Setup(); err != nil {
 		return nil, fmt.Errorf("failed to setup dae netns: %w", err)
 	}
@@ -789,7 +798,7 @@ func (c *ControlPlane) Serve(readyChan chan<- bool, listener *Listener) (err err
 		}
 	}()
 	go func() {
-		buf := pool.GetFullCap(consts.EthernetMtu)
+		buf := pool.GetFullCap(netutils.GetEthernetMtu())
 		var oob [120]byte // Size for original dest
 		defer buf.Put()
 		for {

control/dns.go

@@ -1,7 +1,7 @@
 /*
 *  SPDX-License-Identifier: AGPL-3.0-only
 *  Copyright (c) 2022-2025, daeuniverse Organization <dae@v2raya.org>
-*/
+ */
 
 package control
 
@@ -19,6 +19,7 @@ import (
 
 	"github.com/daeuniverse/dae/common"
 	"github.com/daeuniverse/dae/common/consts"
+	"github.com/daeuniverse/dae/common/netutils"
 	"github.com/daeuniverse/dae/component/dns"
 	"github.com/daeuniverse/outbound/netproxy"
 	"github.com/daeuniverse/outbound/pool"
@@ -346,7 +347,7 @@ func (d *DoUDP) ForwardDNS(ctx context.Context, data []byte) (*dnsmessage.Msg, e
 	}()
 
 	// We can block here because we are in a coroutine.
-	respBuf := pool.GetFullCap(consts.EthernetMtu)
+	respBuf := pool.GetFullCap(netutils.GetEthernetMtu())
 	defer pool.Put(respBuf)
 	// Wait for response.
 	n, err := conn.Read(respBuf)

control/netns_utils.go

@@ -1,7 +1,7 @@
 /*
 *  SPDX-License-Identifier: AGPL-3.0-only
 *  Copyright (c) 2022-2025, daeuniverse Organization <dae@v2raya.org>
-*/
+ */
 
 package control
 
@@ -15,6 +15,7 @@ import (
 	"sync/atomic"
 
 	"github.com/daeuniverse/dae/common/consts"
+	"github.com/daeuniverse/dae/common/netutils"
 	"github.com/sirupsen/logrus"
 	"github.com/vishvananda/netlink"
 	"github.com/vishvananda/netns"
@@ -242,6 +243,10 @@ func (ns *DaeNetns) setupVeth() (err error) {
 	if err = netlink.LinkSetUp(ns.dae0); err != nil {
 		return fmt.Errorf("failed to set link dae0 up: %v", err)
 	}
+
+	if err = netlink.LinkSetMTU(ns.dae0, netutils.GetEthernetMtu()); err != nil {
+		return fmt.Errorf("failed to set mtu %d for dae0: %v", netutils.GetEthernetMtu(), err)
+	}
 	return
 }
 
@@ -269,6 +274,9 @@ func (ns *DaeNetns) setupNetns() (err error) {
 	if err = netlink.LinkSetUp(ns.dae0peer); err != nil {
 		return fmt.Errorf("failed to set link dae0peer up: %v", err)
 	}
+	if err = netlink.LinkSetMTU(ns.dae0peer, netutils.GetEthernetMtu()); err != nil {
+		return fmt.Errorf("failed to set mtu %d for dae0peer: %v", netutils.GetEthernetMtu(), err)
+	}
 	// re-fetch dae0peer to make sure we have the latest mac address
 	if ns.dae0peer, err = netlink.LinkByName(NsVethName); err != nil {
 		return fmt.Errorf("failed to get link dae0peer: %v", err)

control/udp_endpoint_pool.go

@@ -13,6 +13,7 @@ import (
 	"time"
 
 	"github.com/daeuniverse/dae/common/consts"
+	"github.com/daeuniverse/dae/common/netutils"
 	"github.com/daeuniverse/dae/component/outbound"
 	"github.com/daeuniverse/dae/component/outbound/dialer"
 	"github.com/daeuniverse/outbound/netproxy"
@@ -38,7 +39,7 @@ type UdpEndpoint struct {
 }
 
 func (ue *UdpEndpoint) start() {
-	buf := pool.GetFullCap(consts.EthernetMtu)
+	buf := pool.GetFullCap(netutils.GetEthernetMtu())
 	defer pool.Put(buf)
 	for {
 		n, from, err := ue.conn.ReadFrom(buf[:])