diff --git a/if.go b/if.go
new file mode 100644
index 0000000..229d141
--- /dev/null
+++ b/if.go
@@ -0,0 +1,71 @@
+package water
+
+import (
+	"os"
+)
+
+// Interface is a TUN/TAP interface.
+type Interface struct {
+	isTAP bool
+	file  *os.File
+	name  string
+}
+
+// Create a new TAP interface whose name is ifName.
+// If ifName is empty, a default name (tap0, tap1, ... ) will be assigned.
+// ifName should not exceed 16 bytes.
+func NewTAP(ifName string) (ifce *Interface, err error) {
+	file, err := os.OpenFile("/dev/net/tun", os.O_RDWR, 0)
+	if err != nil {
+		return nil, err
+	}
+	name, err := createInterface(file.Fd(), ifName, cIFF_TAP|cIFF_NO_PI)
+	if err != nil {
+		return nil, err
+	}
+	ifce = &Interface{isTAP: true, file: file, name: name}
+	return
+}
+
+// Create a new TUN interface whose name is ifName.
+// If ifName is empty, a default name (tap0, tap1, ... ) will be assigned.
+// ifName should not exceed 16 bytes.
+func NewTUN(ifName string) (ifce *Interface, err error) {
+	file, err := os.OpenFile("/dev/net/tun", os.O_RDWR, 0)
+	if err != nil {
+		return nil, err
+	}
+	name, err := createInterface(file.Fd(), ifName, cIFF_TUN|cIFF_NO_PI)
+	if err != nil {
+		return nil, err
+	}
+	ifce = &Interface{isTAP: false, file: file, name: name}
+	return
+}
+
+// Returns true if ifce is a TUN interface, otherwise returns false;
+func (ifce *Interface) IsTUN() bool {
+	return !ifce.isTAP
+}
+
+// Returns true if ifce is a TAP interface, otherwise returns false;
+func (ifce *Interface) IsTAP() bool {
+	return ifce.isTAP
+}
+
+// Returns the interface name of ifce, e.g. tun0, tap1, etc..
+func (ifce *Interface) Name() string {
+	return ifce.name
+}
+
+// Implement io.Writer interface.
+func (ifce *Interface) Write(p []byte) (n int, err error) {
+	n, err = ifce.file.Write(p)
+	return
+}
+
+// Implement io.Reader interface.
+func (ifce *Interface) Read(p []byte) (n int, err error) {
+	n, err = ifce.file.Read(p)
+	return
+}
diff --git a/syscalls_linux.go b/syscalls_linux.go
new file mode 100644
index 0000000..6bf6c57
--- /dev/null
+++ b/syscalls_linux.go
@@ -0,0 +1,34 @@
+// +build linux
+
+package water
+
+import (
+	"strings"
+	"syscall"
+	"unsafe"
+)
+
+const (
+	cIFF_TUN   = 0x0001
+	cIFF_TAP   = 0x0002
+	cIFF_NO_PI = 0x1000
+)
+
+type ifReq struct {
+	Name  [0x10]byte
+	Flags uint16
+	pad   [0x28 - 0x10 - 2]byte
+}
+
+func createInterface(fd uintptr, ifName string, flags uint16) (createdIFName string, err error) {
+	var req ifReq
+	req.Flags = flags
+	copy(req.Name[:], ifName)
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, fd, uintptr(syscall.TUNSETIFF), uintptr(unsafe.Pointer(&req)))
+	if errno != 0 {
+		err = errno
+		return
+	}
+	createdIFName = strings.Trim(string(req.Name[:]), "\x00")
+	return
+}
diff --git a/waterutil/ethertypes.go b/waterutil/ethertypes.go
new file mode 100644
index 0000000..1d2b1aa
--- /dev/null
+++ b/waterutil/ethertypes.go
@@ -0,0 +1,46 @@
+package waterutil
+
+type Ethertype [2]byte
+
+// Ethertype values. From: http://en.wikipedia.org/wiki/Ethertype
+var (
+	IPv4                = Ethertype{0x08, 0x00}
+	ARP                 = Ethertype{0x08, 0x06}
+	WakeOnLAN           = Ethertype{0x08, 0x42}
+	TRILL               = Ethertype{0x22, 0xF3}
+	DECnetPhase4        = Ethertype{0x60, 0x03}
+	RARP                = Ethertype{0x80, 0x35}
+	AppleTalk           = Ethertype{0x80, 0x9B}
+	AARP                = Ethertype{0x80, 0xF3}
+	IPX1                = Ethertype{0x81, 0x37}
+	IPX2                = Ethertype{0x81, 0x38}
+	QNXQnet             = Ethertype{0x82, 0x04}
+	IPv6                = Ethertype{0x86, 0xDD}
+	EthernetFlowControl = Ethertype{0x88, 0x08}
+	IEEE802_3           = Ethertype{0x88, 0x09}
+	CobraNet            = Ethertype{0x88, 0x19}
+	MPLSUnicast         = Ethertype{0x88, 0x47}
+	MPLSMulticast       = Ethertype{0x88, 0x48}
+	PPPoEDiscovery      = Ethertype{0x88, 0x63}
+	PPPoESession        = Ethertype{0x88, 0x64}
+	JumboFrames         = Ethertype{0x88, 0x70}
+	HomePlug1_0MME      = Ethertype{0x88, 0x7B}
+	IEEE802_1X          = Ethertype{0x88, 0x8E}
+	PROFINET            = Ethertype{0x88, 0x92}
+	HyperSCSI           = Ethertype{0x88, 0x9A}
+	AoE                 = Ethertype{0x88, 0xA2}
+	EtherCAT            = Ethertype{0x88, 0xA4}
+	EthernetPowerlink   = Ethertype{0x88, 0xAB}
+	LLDP                = Ethertype{0x88, 0xCC}
+	SERCOS3             = Ethertype{0x88, 0xCD}
+	HomePlugAVMME       = Ethertype{0x88, 0xE1}
+	MRP                 = Ethertype{0x88, 0xE3}
+	IEEE802_1AE         = Ethertype{0x88, 0xE5}
+	IEEE1588            = Ethertype{0x88, 0xF7}
+	IEEE802_1ag         = Ethertype{0x89, 0x02}
+	FCoE                = Ethertype{0x89, 0x06}
+	FCoEInit            = Ethertype{0x89, 0x14}
+	RoCE                = Ethertype{0x89, 0x15}
+	CTP                 = Ethertype{0x90, 0x00}
+	VeritasLLT          = Ethertype{0xCA, 0xFE}
+)
diff --git a/waterutil/ip_protocols.go b/waterutil/ip_protocols.go
new file mode 100644
index 0000000..2fa1cbe
--- /dev/null
+++ b/waterutil/ip_protocols.go
@@ -0,0 +1,139 @@
+package waterutil
+
+type IPProtocol byte
+
+// IP Protocols. From: http://en.wikipedia.org/wiki/List_of_IP_protocol_numbers
+const (
+	HOPOPT            = 0x00
+	ICMP              = 0x01
+	IGMP              = 0x02
+	GGP               = 0x03
+	IPv4Encapsulation = 0x04
+	ST                = 0x05
+	TCP               = 0x06
+	CBT               = 0x07
+	EGP               = 0x08
+	IGP               = 0x09
+	BBN_RCC_MON       = 0x0A
+	NVP_II            = 0x0B
+	PUP               = 0x0C
+	ARGUS             = 0x0D
+	EMCON             = 0x0E
+	XNET              = 0x0F
+	CHAOS             = 0x10
+	UDP               = 0x11
+	MUX               = 0x12
+	DCN_MEAS          = 0x13
+	HMP               = 0x14
+	PRM               = 0x15
+	XNS_IDP           = 0x16
+	TRUNK_1           = 0x17
+	TRUNK_2           = 0x18
+	LEAF_1            = 0x19
+	LEAF_2            = 0x1A
+	RDP               = 0x1B
+	IRTP              = 0x1C
+	ISO_TP4           = 0x1D
+	NETBLT            = 0x1E
+	MFE_NSP           = 0x1F
+	MERIT_INP         = 0x20
+	DCCP              = 0x21
+	ThirdPC           = 0x22
+	IDPR              = 0x23
+	XTP               = 0x24
+	DDP               = 0x25
+	IDPR_CMTP         = 0x26
+	TPxx              = 0x27
+	IL                = 0x28
+	IPv6Encapsulation = 0x29
+	SDRP              = 0x2A
+	IPv6_Route        = 0x2B
+	IPv6_Frag         = 0x2C
+	IDRP              = 0x2D
+	RSVP              = 0x2E
+	GRE               = 0x2F
+	MHRP              = 0x30
+	BNA               = 0x31
+	ESP               = 0x32
+	AH                = 0x33
+	I_NLSP            = 0x34
+	SWIPE             = 0x35
+	NARP              = 0x36
+	MOBILE            = 0x37
+	TLSP              = 0x38
+	SKIP              = 0x39
+	IPv6_ICMP         = 0x3A
+	IPv6_NoNxt        = 0x3B
+	IPv6_Opts         = 0x3C
+	CFTP              = 0x3E
+	SAT_EXPAK         = 0x40
+	KRYPTOLAN         = 0x41
+	RVD               = 0x42
+	IPPC              = 0x43
+	SAT_MON           = 0x45
+	VISA              = 0x46
+	IPCV              = 0x47
+	CPNX              = 0x48
+	CPHB              = 0x49
+	WSN               = 0x4A
+	PVP               = 0x4B
+	BR_SAT_MON        = 0x4C
+	SUN_ND            = 0x4D
+	WB_MON            = 0x4E
+	WB_EXPAK          = 0x4F
+	ISO_IP            = 0x50
+	VMTP              = 0x51
+	SECURE_VMTP       = 0x52
+	VINES             = 0x53
+	TTP               = 0x54
+	IPTM              = 0x54
+	NSFNET_IGP        = 0x55
+	DGP               = 0x56
+	TCF               = 0x57
+	EIGRP             = 0x58
+	OSPF              = 0x59
+	Sprite_RPC        = 0x5A
+	LARP              = 0x5B
+	MTP               = 0x5C
+	AX_25             = 0x5D
+	IPIP              = 0x5E
+	MICP              = 0x5F
+	SCC_SP            = 0x60
+	ETHERIP           = 0x61
+	ENCAP             = 0x62
+	GMTP              = 0x64
+	IFMP              = 0x65
+	PNNI              = 0x66
+	PIM               = 0x67
+	ARIS              = 0x68
+	SCPS              = 0x69
+	QNX               = 0x6A
+	A_N               = 0x6B
+	IPComp            = 0x6C
+	SNP               = 0x6D
+	Compaq_Peer       = 0x6E
+	IPX_in_IP         = 0x6F
+	VRRP              = 0x70
+	PGM               = 0x71
+	L2TP              = 0x73
+	DDX               = 0x74
+	IATP              = 0x75
+	STP               = 0x76
+	SRP               = 0x77
+	UTI               = 0x78
+	SMP               = 0x79
+	SM                = 0x7A
+	PTP               = 0x7B
+	FIRE              = 0x7D
+	CRTP              = 0x7E
+	CRUDP             = 0x7F
+	SSCOPMCE          = 0x80
+	IPLT              = 0x81
+	SPS               = 0x82
+	PIPE              = 0x83
+	SCTP              = 0x84
+	FC                = 0x85
+	manet             = 0x8A
+	HIP               = 0x8B
+	Shim6             = 0x8C
+)
diff --git a/waterutil/tap.go b/waterutil/tap.go
new file mode 100644
index 0000000..d81da37
--- /dev/null
+++ b/waterutil/tap.go
@@ -0,0 +1,40 @@
+package waterutil
+
+import (
+	"net"
+)
+
+type Tagging int
+
+// Indicating whether/how a MAC frame is tagged. The value is number of bytes taken by tagging.
+const (
+	NotTagged    Tagging = 0
+	Tagged       Tagging = 4
+	DoubleTagged Tagging = 8
+)
+
+func MACDestination(macFrame []byte) net.HardwareAddr {
+	return net.HardwareAddr(macFrame[:6])
+}
+
+func MACSource(macFrame []byte) net.HardwareAddr {
+	return net.HardwareAddr(macFrame[6:12])
+}
+
+func MACTagging(macFrame []byte) Tagging {
+	if macFrame[12] == 0x81 && macFrame[13] == 0x00 {
+		return Tagged
+	} else if macFrame[12] == 0x88 && macFrame[13] == 0xa8 {
+		return DoubleTagged
+	}
+	return NotTagged
+}
+
+func MACEthertype(macFrame []byte) Ethertype {
+	ethertypePos := 12 + MACTagging(macFrame)
+	return Ethertype{macFrame[ethertypePos], macFrame[ethertypePos+1]}
+}
+
+func MACPayload(macFrame []byte) []byte {
+	return macFrame[12+MACTagging(macFrame)+2:]
+}
diff --git a/waterutil/tun.go b/waterutil/tun.go
new file mode 100644
index 0000000..a972e8e
--- /dev/null
+++ b/waterutil/tun.go
@@ -0,0 +1,9 @@
+package waterutil
+
+func IsIPv4(packet []byte) bool {
+	return 4 == (packet[0] >> 4)
+}
+
+func IsIPv6(packet []byte) bool {
+	return 6 == (packet[0] >> 4)
+}
diff --git a/waterutil/tun_ipv4.go b/waterutil/tun_ipv4.go
new file mode 100644
index 0000000..6878174
--- /dev/null
+++ b/waterutil/tun_ipv4.go
@@ -0,0 +1,38 @@
+package waterutil
+
+import (
+	"net"
+)
+
+func IPv4DSCP(packet []byte) byte {
+	return packet[1] >> 2
+}
+
+func IPv4ECN(packet []byte) byte {
+	return packet[1] & 0x03
+}
+
+func IPv4Identification(packet []byte) [2]byte {
+	return [2]byte{packet[4], packet[5]}
+}
+
+func IPv4TTL(packet []byte) byte {
+	return packet[8]
+}
+
+func IPv4Protocol(packet []byte) IPProtocol {
+	return IPProtocol(packet[9])
+}
+
+func IPv4Source(packet []byte) net.IP {
+	return net.IPv4(packet[12], packet[13], packet[14], packet[15])
+}
+
+func IPv4Destination(packet []byte) net.IP {
+	return net.IPv4(packet[16], packet[17], packet[18], packet[19])
+}
+
+func IPv4Payload(packet []byte) []byte {
+	ihl := packet[0] & 0x0F
+	return packet[ihl*4:]
+}