diff --git a/gold/link/crypto.go b/gold/link/crypto.go
index bc79e3d..a09dce1 100644
--- a/gold/link/crypto.go
+++ b/gold/link/crypto.go
@@ -1,73 +1,11 @@
 package link
 
 import (
-	"net"
-	"sync"
 	"unsafe"
 
 	tea "github.com/fumiama/gofastTEA"
-
-	"github.com/fumiama/WireGold/gold/head"
 )
 
-// Me 是本机的抽象
-type Me struct {
-	// 本机私钥
-	// 利用 Curve25519 生成
-	// https://pkg.go.dev/golang.org/x/crypto/curve25519
-	// https://www.zhihu.com/question/266758647
-	privKey [32]byte
-	// 本机虚拟 ip
-	me net.IP
-	// 本机子网
-	subnet net.IPNet
-	// 本机 endpoint
-	myend *net.UDPAddr
-	// 本机环回 link
-	loop *Link
-	// 本机活跃的所有连接
-	connections map[string]*Link
-	// 读写同步锁
-	connmapmu sync.RWMutex
-	// 本机监听的 endpoint
-	myconn *net.UDPConn
-	// 不分目的 link 的接收队列
-	pipe chan *head.Packet
-	// 本机路由表
-	router *Router
-}
-
-// NewMe 设置本机参数
-func NewMe(privateKey *[32]byte, myipwithmask string, myEndpoint string, nopipeinlink bool) (m Me) {
-	m.privKey = *privateKey
-	var err error
-	m.myend, err = net.ResolveUDPAddr("udp", myEndpoint)
-	if err != nil {
-		panic(err)
-	}
-	ip, cidr, err := net.ParseCIDR(myipwithmask)
-	if err != nil {
-		panic(err)
-	}
-	m.me = ip
-	m.subnet = *cidr
-	m.myconn, err = m.listen()
-	if err != nil {
-		panic(err)
-	}
-	m.connections = make(map[string]*Link)
-	if nopipeinlink {
-		m.pipe = make(chan *head.Packet, 32)
-	}
-	m.router = &Router{
-		list:  make([]*net.IPNet, 1, 16),
-		table: make(map[string]*Link, 16),
-	}
-	m.router.SetDefault(nil)
-	m.loop = m.AddPeer(m.me.String(), nil, "127.0.0.1:56789", []string{myipwithmask}, 0, false, nopipeinlink)
-	return
-}
-
 // Encode 使用 TEA 加密
 func (l *Link) Encode(b []byte) (eb []byte) {
 	if b == nil {
diff --git a/gold/link/link.go b/gold/link/link.go
index 225de2e..53e180b 100644
--- a/gold/link/link.go
+++ b/gold/link/link.go
@@ -75,6 +75,39 @@ func (l *Link) Read() *head.Packet {
 
 // Write 向 peer 发包
 func (l *Link) Write(p *head.Packet, istransfer bool) (n int, err error) {
+	if len(p.Data) <= int(l.me.mtu) {
+		return l.write(p, istransfer)
+	}
+	data := p.Data
+	offset := 0
+	for len(data) > int(l.me.mtu) {
+		packet := *p
+		packet.Data = data[offset*int(l.me.mtu) : (offset+1)*int(l.me.mtu)]
+		i, err := l.write(&packet, istransfer)
+		n += i
+		if err != nil {
+			return n, err
+		}
+		data = data[(offset+1)*int(l.me.mtu):]
+	}
+	return n, nil
+}
+
+func (l *Link) String() (n string) {
+	n = "default"
+	if l.pubk != nil {
+		b, err := base14.UTF16be2utf8(base14.Encode(l.pubk[:10]))
+		if err == nil {
+			n = helper.BytesToString(b)
+		} else {
+			n = err.Error()
+		}
+	}
+	return
+}
+
+// write 向 peer 发一个包
+func (l *Link) write(p *head.Packet, istransfer bool) (n int, err error) {
 	var d []byte
 	if istransfer {
 		d = p.Marshal(nil)
@@ -102,16 +135,3 @@ func (l *Link) Write(p *head.Packet, istransfer bool) (n int, err error) {
 	}
 	return
 }
-
-func (l *Link) String() (n string) {
-	n = "default"
-	if l.pubk != nil {
-		b, err := base14.UTF16be2utf8(base14.Encode(l.pubk[:10]))
-		if err == nil {
-			n = helper.BytesToString(b)
-		} else {
-			n = err.Error()
-		}
-	}
-	return
-}
diff --git a/gold/link/me.go b/gold/link/me.go
new file mode 100644
index 0000000..9a5fdc3
--- /dev/null
+++ b/gold/link/me.go
@@ -0,0 +1,74 @@
+package link
+
+import (
+	"net"
+	"sync"
+
+	"github.com/fumiama/WireGold/gold/head"
+)
+
+// Me 是本机的抽象
+type Me struct {
+	// 本机私钥
+	// 利用 Curve25519 生成
+	// https://pkg.go.dev/golang.org/x/crypto/curve25519
+	// https://www.zhihu.com/question/266758647
+	privKey [32]byte
+	// 本机虚拟 ip
+	me net.IP
+	// 本机子网
+	subnet net.IPNet
+	// 本机 endpoint
+	myend *net.UDPAddr
+	// 本机环回 link
+	loop *Link
+	// 本机活跃的所有连接
+	connections map[string]*Link
+	// 读写同步锁
+	connmapmu sync.RWMutex
+	// 本机监听的 endpoint
+	myconn *net.UDPConn
+	// 不分目的 link 的接收队列
+	pipe chan *head.Packet
+	// 本机路由表
+	router *Router
+	// 虚拟链路网卡 MTU
+	// 默认 30000
+	mtu uint16
+}
+
+// NewMe 设置本机参数
+func NewMe(privateKey *[32]byte, myipwithmask string, myEndpoint string, nopipeinlink bool) (m Me) {
+	m.privKey = *privateKey
+	var err error
+	m.myend, err = net.ResolveUDPAddr("udp", myEndpoint)
+	if err != nil {
+		panic(err)
+	}
+	ip, cidr, err := net.ParseCIDR(myipwithmask)
+	if err != nil {
+		panic(err)
+	}
+	m.me = ip
+	m.subnet = *cidr
+	m.myconn, err = m.listen()
+	if err != nil {
+		panic(err)
+	}
+	m.connections = make(map[string]*Link)
+	if nopipeinlink {
+		m.pipe = make(chan *head.Packet, 32)
+	}
+	m.router = &Router{
+		list:  make([]*net.IPNet, 1, 16),
+		table: make(map[string]*Link, 16),
+	}
+	m.router.SetDefault(nil)
+	m.loop = m.AddPeer(m.me.String(), nil, "127.0.0.1:56789", []string{myipwithmask}, 0, false, nopipeinlink)
+	m.mtu = 30000
+	return
+}
+
+func (m *Me) SetMTU(mtu uint16) {
+	m.mtu = mtu
+}
diff --git a/lower/nic.go b/lower/nic.go
index b07fb8a..ce97cc8 100644
--- a/lower/nic.go
+++ b/lower/nic.go
@@ -57,8 +57,8 @@ func (nc *NIC) Start(m *link.Me) {
 			logrus.Infoln("[lower] recv write", n, "bytes packet to nic")
 		}
 	}()
-	buf := make([]byte, 4096)
-	for nc.hasstart { // 从 NIC 发送
+	buf := make([]byte, 32768) // Ring capacity
+	for nc.hasstart {          // 从 NIC 发送
 		packet := buf
 		n, err := nc.ifce.Read(packet)
 		if err != nil {