Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

15 files changed, 1998 insertions, 0 deletions

diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
new file mode 100644
index 000000000..167ea250d
--- /dev/null
+++ b/pkg/tcpip/header/BUILD
@@ -0,0 +1,51 @@
+package(licenses = ["notice"])  # BSD
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+load("//tools/go_stateify:defs.bzl", "go_stateify")
+
+go_stateify(
+    name = "tcp_header_state",
+    srcs = [
+        "tcp.go",
+    ],
+    out = "tcp_header_state.go",
+    package = "header",
+)
+
+go_library(
+    name = "header",
+    srcs = [
+        "arp.go",
+        "checksum.go",
+        "eth.go",
+        "gue.go",
+        "icmpv4.go",
+        "icmpv6.go",
+        "interfaces.go",
+        "ipv4.go",
+        "ipv6.go",
+        "ipv6_fragment.go",
+        "tcp.go",
+        "tcp_header_state.go",
+        "udp.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/tcpip/header",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/state",
+        "//pkg/tcpip",
+        "//pkg/tcpip/seqnum",
+    ],
+)
+
+go_test(
+    name = "header_test",
+    size = "small",
+    srcs = [
+        "ipversion_test.go",
+        "tcp_test.go",
+    ],
+    deps = [
+        ":header",
+    ],
+)
diff --git a/pkg/tcpip/header/arp.go b/pkg/tcpip/header/arp.go
new file mode 100644
index 000000000..af7f988f3
--- /dev/null
+++ b/pkg/tcpip/header/arp.go
@@ -0,0 +1,90 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import "gvisor.googlesource.com/gvisor/pkg/tcpip"
+
+const (
+	// ARPProtocolNumber is the ARP network protocol number.
+	ARPProtocolNumber tcpip.NetworkProtocolNumber = 0x0806
+
+	// ARPSize is the size of an IPv4-over-Ethernet ARP packet.
+	ARPSize = 2 + 2 + 1 + 1 + 2 + 2*6 + 2*4
+)
+
+// ARPOp is an ARP opcode.
+type ARPOp uint16
+
+// Typical ARP opcodes defined in RFC 826.
+const (
+	ARPRequest ARPOp = 1
+	ARPReply   ARPOp = 2
+)
+
+// ARP is an ARP packet stored in a byte array as described in RFC 826.
+type ARP []byte
+
+func (a ARP) hardwareAddressSpace() uint16 { return uint16(a[0])<<8 | uint16(a[1]) }
+func (a ARP) protocolAddressSpace() uint16 { return uint16(a[2])<<8 | uint16(a[3]) }
+func (a ARP) hardwareAddressSize() int     { return int(a[4]) }
+func (a ARP) protocolAddressSize() int     { return int(a[5]) }
+
+// Op is the ARP opcode.
+func (a ARP) Op() ARPOp { return ARPOp(a[6])<<8 | ARPOp(a[7]) }
+
+// SetOp sets the ARP opcode.
+func (a ARP) SetOp(op ARPOp) {
+	a[6] = uint8(op >> 8)
+	a[7] = uint8(op)
+}
+
+// SetIPv4OverEthernet configures the ARP packet for IPv4-over-Ethernet.
+func (a ARP) SetIPv4OverEthernet() {
+	a[0], a[1] = 0, 1       // htypeEthernet
+	a[2], a[3] = 0x08, 0x00 // IPv4ProtocolNumber
+	a[4] = 6                // macSize
+	a[5] = uint8(IPv4AddressSize)
+}
+
+// HardwareAddressSender is the link address of the sender.
+// It is a view on to the ARP packet so it can be used to set the value.
+func (a ARP) HardwareAddressSender() []byte {
+	const s = 8
+	return a[s : s+6]
+}
+
+// ProtocolAddressSender is the protocol address of the sender.
+// It is a view on to the ARP packet so it can be used to set the value.
+func (a ARP) ProtocolAddressSender() []byte {
+	const s = 8 + 6
+	return a[s : s+4]
+}
+
+// HardwareAddressTarget is the link address of the target.
+// It is a view on to the ARP packet so it can be used to set the value.
+func (a ARP) HardwareAddressTarget() []byte {
+	const s = 8 + 6 + 4
+	return a[s : s+6]
+}
+
+// ProtocolAddressTarget is the protocol address of the target.
+// It is a view on to the ARP packet so it can be used to set the value.
+func (a ARP) ProtocolAddressTarget() []byte {
+	const s = 8 + 6 + 4 + 6
+	return a[s : s+4]
+}
+
+// IsValid reports whether this is an ARP packet for IPv4 over Ethernet.
+func (a ARP) IsValid() bool {
+	if len(a) < ARPSize {
+		return false
+	}
+	const htypeEthernet = 1
+	const macSize = 6
+	return a.hardwareAddressSpace() == htypeEthernet &&
+		a.protocolAddressSpace() == uint16(IPv4ProtocolNumber) &&
+		a.hardwareAddressSize() == macSize &&
+		a.protocolAddressSize() == IPv4AddressSize
+}
diff --git a/pkg/tcpip/header/checksum.go b/pkg/tcpip/header/checksum.go
new file mode 100644
index 000000000..6399b1b95
--- /dev/null
+++ b/pkg/tcpip/header/checksum.go
@@ -0,0 +1,46 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package header provides the implementation of the encoding and decoding of
+// network protocol headers.
+package header
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
+// given byte array.
+func Checksum(buf []byte, initial uint16) uint16 {
+	v := uint32(initial)
+
+	l := len(buf)
+	if l&1 != 0 {
+		l--
+		v += uint32(buf[l]) << 8
+	}
+
+	for i := 0; i < l; i += 2 {
+		v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
+	}
+
+	return ChecksumCombine(uint16(v), uint16(v>>16))
+}
+
+// ChecksumCombine combines the two uint16 to form their checksum. This is done
+// by adding them and the carry.
+func ChecksumCombine(a, b uint16) uint16 {
+	v := uint32(a) + uint32(b)
+	return uint16(v + v>>16)
+}
+
+// PseudoHeaderChecksum calculates the pseudo-header checksum for the
+// given destination protocol and network address, ignoring the length
+// field. Pseudo-headers are needed by transport layers when calculating
+// their own checksum.
+func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address) uint16 {
+	xsum := Checksum([]byte(srcAddr), 0)
+	xsum = Checksum([]byte(dstAddr), xsum)
+	return Checksum([]byte{0, uint8(protocol)}, xsum)
+}
diff --git a/pkg/tcpip/header/eth.go b/pkg/tcpip/header/eth.go
new file mode 100644
index 000000000..23b7efdfc
--- /dev/null
+++ b/pkg/tcpip/header/eth.go
@@ -0,0 +1,64 @@
+// Copyright 2017 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	dstMAC  = 0
+	srcMAC  = 6
+	ethType = 12
+)
+
+// EthernetFields contains the fields of an ethernet frame header. It is used to
+// describe the fields of a frame that needs to be encoded.
+type EthernetFields struct {
+	// SrcAddr is the "MAC source" field of an ethernet frame header.
+	SrcAddr tcpip.LinkAddress
+
+	// DstAddr is the "MAC destination" field of an ethernet frame header.
+	DstAddr tcpip.LinkAddress
+
+	// Type is the "ethertype" field of an ethernet frame header.
+	Type tcpip.NetworkProtocolNumber
+}
+
+// Ethernet represents an ethernet frame header stored in a byte array.
+type Ethernet []byte
+
+const (
+	// EthernetMinimumSize is the minimum size of a valid ethernet frame.
+	EthernetMinimumSize = 14
+
+	// EthernetAddressSize is the size, in bytes, of an ethernet address.
+	EthernetAddressSize = 6
+)
+
+// SourceAddress returns the "MAC source" field of the ethernet frame header.
+func (b Ethernet) SourceAddress() tcpip.LinkAddress {
+	return tcpip.LinkAddress(b[srcMAC:][:EthernetAddressSize])
+}
+
+// DestinationAddress returns the "MAC destination" field of the ethernet frame
+// header.
+func (b Ethernet) DestinationAddress() tcpip.LinkAddress {
+	return tcpip.LinkAddress(b[dstMAC:][:EthernetAddressSize])
+}
+
+// Type returns the "ethertype" field of the ethernet frame header.
+func (b Ethernet) Type() tcpip.NetworkProtocolNumber {
+	return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(b[ethType:]))
+}
+
+// Encode encodes all the fields of the ethernet frame header.
+func (b Ethernet) Encode(e *EthernetFields) {
+	binary.BigEndian.PutUint16(b[ethType:], uint16(e.Type))
+	copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr)
+	copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr)
+}
diff --git a/pkg/tcpip/header/gue.go b/pkg/tcpip/header/gue.go
new file mode 100644
index 000000000..a069fb669
--- /dev/null
+++ b/pkg/tcpip/header/gue.go
@@ -0,0 +1,63 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+const (
+	typeHLen   = 0
+	encapProto = 1
+)
+
+// GUEFields contains the fields of a GUE packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type GUEFields struct {
+	// Type is the "type" field of the GUE header.
+	Type uint8
+
+	// Control is the "control" field of the GUE header.
+	Control bool
+
+	// HeaderLength is the "header length" field of the GUE header. It must
+	// be at least 4 octets, and a multiple of 4 as well.
+	HeaderLength uint8
+
+	// Protocol is the "protocol" field of the GUE header. This is one of
+	// the IPPROTO_* values.
+	Protocol uint8
+}
+
+// GUE represents a Generic UDP Encapsulation header stored in a byte array, the
+// fields are described in https://tools.ietf.org/html/draft-ietf-nvo3-gue-01.
+type GUE []byte
+
+const (
+	// GUEMinimumSize is the minimum size of a valid GUE packet.
+	GUEMinimumSize = 4
+)
+
+// TypeAndControl returns the GUE packet type (top 3 bits of the first byte,
+// which includes the control bit).
+func (b GUE) TypeAndControl() uint8 {
+	return b[typeHLen] >> 5
+}
+
+// HeaderLength returns the total length of the GUE header.
+func (b GUE) HeaderLength() uint8 {
+	return 4 + 4*(b[typeHLen]&0x1f)
+}
+
+// Protocol returns the protocol field of the GUE header.
+func (b GUE) Protocol() uint8 {
+	return b[encapProto]
+}
+
+// Encode encodes all the fields of the GUE header.
+func (b GUE) Encode(i *GUEFields) {
+	ctl := uint8(0)
+	if i.Control {
+		ctl = 1 << 5
+	}
+	b[typeHLen] = ctl | i.Type<<6 | (i.HeaderLength-4)/4
+	b[encapProto] = i.Protocol
+}
diff --git a/pkg/tcpip/header/icmpv4.go b/pkg/tcpip/header/icmpv4.go
new file mode 100644
index 000000000..9f1ad38fc
--- /dev/null
+++ b/pkg/tcpip/header/icmpv4.go
@@ -0,0 +1,98 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+// ICMPv4 represents an ICMPv4 header stored in a byte array.
+type ICMPv4 []byte
+
+const (
+	// ICMPv4MinimumSize is the minimum size of a valid ICMP packet.
+	ICMPv4MinimumSize = 4
+
+	// ICMPv4EchoMinimumSize is the minimum size of a valid ICMP echo packet.
+	ICMPv4EchoMinimumSize = 6
+
+	// ICMPv4DstUnreachableMinimumSize is the minimum size of a valid ICMP
+	// destination unreachable packet.
+	ICMPv4DstUnreachableMinimumSize = ICMPv4MinimumSize + 4
+
+	// ICMPv4ProtocolNumber is the ICMP transport protocol number.
+	ICMPv4ProtocolNumber tcpip.TransportProtocolNumber = 1
+)
+
+// ICMPv4Type is the ICMP type field described in RFC 792.
+type ICMPv4Type byte
+
+// Typical values of ICMPv4Type defined in RFC 792.
+const (
+	ICMPv4EchoReply      ICMPv4Type = 0
+	ICMPv4DstUnreachable ICMPv4Type = 3
+	ICMPv4SrcQuench      ICMPv4Type = 4
+	ICMPv4Redirect       ICMPv4Type = 5
+	ICMPv4Echo           ICMPv4Type = 8
+	ICMPv4TimeExceeded   ICMPv4Type = 11
+	ICMPv4ParamProblem   ICMPv4Type = 12
+	ICMPv4Timestamp      ICMPv4Type = 13
+	ICMPv4TimestampReply ICMPv4Type = 14
+	ICMPv4InfoRequest    ICMPv4Type = 15
+	ICMPv4InfoReply      ICMPv4Type = 16
+)
+
+// Values for ICMP code as defined in RFC 792.
+const (
+	ICMPv4PortUnreachable     = 3
+	ICMPv4FragmentationNeeded = 4
+)
+
+// Type is the ICMP type field.
+func (b ICMPv4) Type() ICMPv4Type { return ICMPv4Type(b[0]) }
+
+// SetType sets the ICMP type field.
+func (b ICMPv4) SetType(t ICMPv4Type) { b[0] = byte(t) }
+
+// Code is the ICMP code field. Its meaning depends on the value of Type.
+func (b ICMPv4) Code() byte { return b[1] }
+
+// SetCode sets the ICMP code field.
+func (b ICMPv4) SetCode(c byte) { b[1] = c }
+
+// Checksum is the ICMP checksum field.
+func (b ICMPv4) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[2:])
+}
+
+// SetChecksum sets the ICMP checksum field.
+func (b ICMPv4) SetChecksum(checksum uint16) {
+	binary.BigEndian.PutUint16(b[2:], checksum)
+}
+
+// SourcePort implements Transport.SourcePort.
+func (ICMPv4) SourcePort() uint16 {
+	return 0
+}
+
+// DestinationPort implements Transport.DestinationPort.
+func (ICMPv4) DestinationPort() uint16 {
+	return 0
+}
+
+// SetSourcePort implements Transport.SetSourcePort.
+func (ICMPv4) SetSourcePort(uint16) {
+}
+
+// SetDestinationPort implements Transport.SetDestinationPort.
+func (ICMPv4) SetDestinationPort(uint16) {
+}
+
+// Payload implements Transport.Payload.
+func (b ICMPv4) Payload() []byte {
+	return b[ICMPv4MinimumSize:]
+}
diff --git a/pkg/tcpip/header/icmpv6.go b/pkg/tcpip/header/icmpv6.go
new file mode 100644
index 000000000..a061cd02b
--- /dev/null
+++ b/pkg/tcpip/header/icmpv6.go
@@ -0,0 +1,111 @@
+// Copyright 2017 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+// ICMPv6 represents an ICMPv6 header stored in a byte array.
+type ICMPv6 []byte
+
+const (
+	// ICMPv6MinimumSize is the minimum size of a valid ICMP packet.
+	ICMPv6MinimumSize = 4
+
+	// ICMPv6ProtocolNumber is the ICMP transport protocol number.
+	ICMPv6ProtocolNumber tcpip.TransportProtocolNumber = 58
+
+	// ICMPv6NeighborSolicitMinimumSize is the minimum size of a
+	// neighbor solicitation packet.
+	ICMPv6NeighborSolicitMinimumSize = ICMPv6MinimumSize + 4 + 16
+
+	// ICMPv6NeighborAdvertSize is size of a neighbor advertisement.
+	ICMPv6NeighborAdvertSize = 32
+
+	// ICMPv6EchoMinimumSize is the minimum size of a valid ICMP echo packet.
+	ICMPv6EchoMinimumSize = 8
+
+	// ICMPv6DstUnreachableMinimumSize is the minimum size of a valid ICMP
+	// destination unreachable packet.
+	ICMPv6DstUnreachableMinimumSize = ICMPv6MinimumSize + 4
+
+	// ICMPv6PacketTooBigMinimumSize is the minimum size of a valid ICMP
+	// packet-too-big packet.
+	ICMPv6PacketTooBigMinimumSize = ICMPv6MinimumSize + 4
+)
+
+// ICMPv6Type is the ICMP type field described in RFC 4443 and friends.
+type ICMPv6Type byte
+
+// Typical values of ICMPv6Type defined in RFC 4443.
+const (
+	ICMPv6DstUnreachable ICMPv6Type = 1
+	ICMPv6PacketTooBig   ICMPv6Type = 2
+	ICMPv6TimeExceeded   ICMPv6Type = 3
+	ICMPv6ParamProblem   ICMPv6Type = 4
+	ICMPv6EchoRequest    ICMPv6Type = 128
+	ICMPv6EchoReply      ICMPv6Type = 129
+
+	// Neighbor Discovery Protocol (NDP) messages, see RFC 4861.
+
+	ICMPv6RouterSolicit   ICMPv6Type = 133
+	ICMPv6RouterAdvert    ICMPv6Type = 134
+	ICMPv6NeighborSolicit ICMPv6Type = 135
+	ICMPv6NeighborAdvert  ICMPv6Type = 136
+	ICMPv6RedirectMsg     ICMPv6Type = 137
+)
+
+// Values for ICMP code as defined in RFC 4443.
+const (
+	ICMPv6PortUnreachable = 4
+)
+
+// Type is the ICMP type field.
+func (b ICMPv6) Type() ICMPv6Type { return ICMPv6Type(b[0]) }
+
+// SetType sets the ICMP type field.
+func (b ICMPv6) SetType(t ICMPv6Type) { b[0] = byte(t) }
+
+// Code is the ICMP code field. Its meaning depends on the value of Type.
+func (b ICMPv6) Code() byte { return b[1] }
+
+// SetCode sets the ICMP code field.
+func (b ICMPv6) SetCode(c byte) { b[1] = c }
+
+// Checksum is the ICMP checksum field.
+func (b ICMPv6) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[2:])
+}
+
+// SetChecksum calculates and sets the ICMP checksum field.
+func (b ICMPv6) SetChecksum(checksum uint16) {
+	binary.BigEndian.PutUint16(b[2:], checksum)
+}
+
+// SourcePort implements Transport.SourcePort.
+func (ICMPv6) SourcePort() uint16 {
+	return 0
+}
+
+// DestinationPort implements Transport.DestinationPort.
+func (ICMPv6) DestinationPort() uint16 {
+	return 0
+}
+
+// SetSourcePort implements Transport.SetSourcePort.
+func (ICMPv6) SetSourcePort(uint16) {
+}
+
+// SetDestinationPort implements Transport.SetDestinationPort.
+func (ICMPv6) SetDestinationPort(uint16) {
+}
+
+// Payload implements Transport.Payload.
+func (b ICMPv6) Payload() []byte {
+	return b[ICMPv6MinimumSize:]
+}
diff --git a/pkg/tcpip/header/interfaces.go b/pkg/tcpip/header/interfaces.go
new file mode 100644
index 000000000..a92286761
--- /dev/null
+++ b/pkg/tcpip/header/interfaces.go
@@ -0,0 +1,82 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	// MaxIPPacketSize is the maximum supported IP packet size, excluding
+	// jumbograms. The maximum IPv4 packet size is 64k-1 (total size must fit
+	// in 16 bits). For IPv6, the payload max size (excluding jumbograms) is
+	// 64k-1 (also needs to fit in 16 bits). So we use 64k - 1 + 2 * m, where
+	// m is the minimum IPv6 header size; we leave room for some potential
+	// IP options.
+	MaxIPPacketSize = 0xffff + 2*IPv6MinimumSize
+)
+
+// Transport offers generic methods to query and/or update the fields of the
+// header of a transport protocol buffer.
+type Transport interface {
+	// SourcePort returns the value of the "source port" field.
+	SourcePort() uint16
+
+	// Destination returns the value of the "destination port" field.
+	DestinationPort() uint16
+
+	// Checksum returns the value of the "checksum" field.
+	Checksum() uint16
+
+	// SetSourcePort sets the value of the "source port" field.
+	SetSourcePort(uint16)
+
+	// SetDestinationPort sets the value of the "destination port" field.
+	SetDestinationPort(uint16)
+
+	// SetChecksum sets the value of the "checksum" field.
+	SetChecksum(uint16)
+
+	// Payload returns the data carried in the transport buffer.
+	Payload() []byte
+}
+
+// Network offers generic methods to query and/or update the fields of the
+// header of a network protocol buffer.
+type Network interface {
+	// SourceAddress returns the value of the "source address" field.
+	SourceAddress() tcpip.Address
+
+	// DestinationAddress returns the value of the "destination address"
+	// field.
+	DestinationAddress() tcpip.Address
+
+	// Checksum returns the value of the "checksum" field.
+	Checksum() uint16
+
+	// SetSourceAddress sets the value of the "source address" field.
+	SetSourceAddress(tcpip.Address)
+
+	// SetDestinationAddress sets the value of the "destination address"
+	// field.
+	SetDestinationAddress(tcpip.Address)
+
+	// SetChecksum sets the value of the "checksum" field.
+	SetChecksum(uint16)
+
+	// TransportProtocol returns the number of the transport protocol
+	// stored in the payload.
+	TransportProtocol() tcpip.TransportProtocolNumber
+
+	// Payload returns a byte slice containing the payload of the network
+	// packet.
+	Payload() []byte
+
+	// TOS returns the values of the "type of service" and "flow label" fields.
+	TOS() (uint8, uint32)
+
+	// SetTOS sets the values of the "type of service" and "flow label" fields.
+	SetTOS(t uint8, l uint32)
+}
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go
new file mode 100644
index 000000000..cb0d42093
--- /dev/null
+++ b/pkg/tcpip/header/ipv4.go
@@ -0,0 +1,251 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	versIHL  = 0
+	tos      = 1
+	totalLen = 2
+	id       = 4
+	flagsFO  = 6
+	ttl      = 8
+	protocol = 9
+	checksum = 10
+	srcAddr  = 12
+	dstAddr  = 16
+)
+
+// IPv4Fields contains the fields of an IPv4 packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type IPv4Fields struct {
+	// IHL is the "internet header length" field of an IPv4 packet.
+	IHL uint8
+
+	// TOS is the "type of service" field of an IPv4 packet.
+	TOS uint8
+
+	// TotalLength is the "total length" field of an IPv4 packet.
+	TotalLength uint16
+
+	// ID is the "identification" field of an IPv4 packet.
+	ID uint16
+
+	// Flags is the "flags" field of an IPv4 packet.
+	Flags uint8
+
+	// FragmentOffset is the "fragment offset" field of an IPv4 packet.
+	FragmentOffset uint16
+
+	// TTL is the "time to live" field of an IPv4 packet.
+	TTL uint8
+
+	// Protocol is the "protocol" field of an IPv4 packet.
+	Protocol uint8
+
+	// Checksum is the "checksum" field of an IPv4 packet.
+	Checksum uint16
+
+	// SrcAddr is the "source ip address" of an IPv4 packet.
+	SrcAddr tcpip.Address
+
+	// DstAddr is the "destination ip address" of an IPv4 packet.
+	DstAddr tcpip.Address
+}
+
+// IPv4 represents an ipv4 header stored in a byte array.
+// Most of the methods of IPv4 access to the underlying slice without
+// checking the boundaries and could panic because of 'index out of range'.
+// Always call IsValid() to validate an instance of IPv4 before using other methods.
+type IPv4 []byte
+
+const (
+	// IPv4MinimumSize is the minimum size of a valid IPv4 packet.
+	IPv4MinimumSize = 20
+
+	// IPv4MaximumHeaderSize is the maximum size of an IPv4 header. Given
+	// that there are only 4 bits to represents the header length in 32-bit
+	// units, the header cannot exceed 15*4 = 60 bytes.
+	IPv4MaximumHeaderSize = 60
+
+	// IPv4AddressSize is the size, in bytes, of an IPv4 address.
+	IPv4AddressSize = 4
+
+	// IPv4ProtocolNumber is IPv4's network protocol number.
+	IPv4ProtocolNumber tcpip.NetworkProtocolNumber = 0x0800
+
+	// IPv4Version is the version of the ipv4 procotol.
+	IPv4Version = 4
+)
+
+// Flags that may be set in an IPv4 packet.
+const (
+	IPv4FlagMoreFragments = 1 << iota
+	IPv4FlagDontFragment
+)
+
+// IPVersion returns the version of IP used in the given packet. It returns -1
+// if the packet is not large enough to contain the version field.
+func IPVersion(b []byte) int {
+	// Length must be at least offset+length of version field.
+	if len(b) < versIHL+1 {
+		return -1
+	}
+	return int(b[versIHL] >> 4)
+}
+
+// HeaderLength returns the value of the "header length" field of the ipv4
+// header.
+func (b IPv4) HeaderLength() uint8 {
+	return (b[versIHL] & 0xf) * 4
+}
+
+// ID returns the value of the identifier field of the ipv4 header.
+func (b IPv4) ID() uint16 {
+	return binary.BigEndian.Uint16(b[id:])
+}
+
+// Protocol returns the value of the protocol field of the ipv4 header.
+func (b IPv4) Protocol() uint8 {
+	return b[protocol]
+}
+
+// Flags returns the "flags" field of the ipv4 header.
+func (b IPv4) Flags() uint8 {
+	return uint8(binary.BigEndian.Uint16(b[flagsFO:]) >> 13)
+}
+
+// TTL returns the "TTL" field of the ipv4 header.
+func (b IPv4) TTL() uint8 {
+	return b[ttl]
+}
+
+// FragmentOffset returns the "fragment offset" field of the ipv4 header.
+func (b IPv4) FragmentOffset() uint16 {
+	return binary.BigEndian.Uint16(b[flagsFO:]) << 3
+}
+
+// TotalLength returns the "total length" field of the ipv4 header.
+func (b IPv4) TotalLength() uint16 {
+	return binary.BigEndian.Uint16(b[totalLen:])
+}
+
+// Checksum returns the checksum field of the ipv4 header.
+func (b IPv4) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[checksum:])
+}
+
+// SourceAddress returns the "source address" field of the ipv4 header.
+func (b IPv4) SourceAddress() tcpip.Address {
+	return tcpip.Address(b[srcAddr : srcAddr+IPv4AddressSize])
+}
+
+// DestinationAddress returns the "destination address" field of the ipv4
+// header.
+func (b IPv4) DestinationAddress() tcpip.Address {
+	return tcpip.Address(b[dstAddr : dstAddr+IPv4AddressSize])
+}
+
+// TransportProtocol implements Network.TransportProtocol.
+func (b IPv4) TransportProtocol() tcpip.TransportProtocolNumber {
+	return tcpip.TransportProtocolNumber(b.Protocol())
+}
+
+// Payload implements Network.Payload.
+func (b IPv4) Payload() []byte {
+	return b[b.HeaderLength():][:b.PayloadLength()]
+}
+
+// PayloadLength returns the length of the payload portion of the ipv4 packet.
+func (b IPv4) PayloadLength() uint16 {
+	return b.TotalLength() - uint16(b.HeaderLength())
+}
+
+// TOS returns the "type of service" field of the ipv4 header.
+func (b IPv4) TOS() (uint8, uint32) {
+	return b[tos], 0
+}
+
+// SetTOS sets the "type of service" field of the ipv4 header.
+func (b IPv4) SetTOS(v uint8, _ uint32) {
+	b[tos] = v
+}
+
+// SetTotalLength sets the "total length" field of the ipv4 header.
+func (b IPv4) SetTotalLength(totalLength uint16) {
+	binary.BigEndian.PutUint16(b[totalLen:], totalLength)
+}
+
+// SetChecksum sets the checksum field of the ipv4 header.
+func (b IPv4) SetChecksum(v uint16) {
+	binary.BigEndian.PutUint16(b[checksum:], v)
+}
+
+// SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the
+// ipv4 header.
+func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16) {
+	v := (uint16(flags) << 13) | (offset >> 3)
+	binary.BigEndian.PutUint16(b[flagsFO:], v)
+}
+
+// SetSourceAddress sets the "source address" field of the ipv4 header.
+func (b IPv4) SetSourceAddress(addr tcpip.Address) {
+	copy(b[srcAddr:srcAddr+IPv4AddressSize], addr)
+}
+
+// SetDestinationAddress sets the "destination address" field of the ipv4
+// header.
+func (b IPv4) SetDestinationAddress(addr tcpip.Address) {
+	copy(b[dstAddr:dstAddr+IPv4AddressSize], addr)
+}
+
+// CalculateChecksum calculates the checksum of the ipv4 header.
+func (b IPv4) CalculateChecksum() uint16 {
+	return Checksum(b[:b.HeaderLength()], 0)
+}
+
+// Encode encodes all the fields of the ipv4 header.
+func (b IPv4) Encode(i *IPv4Fields) {
+	b[versIHL] = (4 << 4) | ((i.IHL / 4) & 0xf)
+	b[tos] = i.TOS
+	b.SetTotalLength(i.TotalLength)
+	binary.BigEndian.PutUint16(b[id:], i.ID)
+	b.SetFlagsFragmentOffset(i.Flags, i.FragmentOffset)
+	b[ttl] = i.TTL
+	b[protocol] = i.Protocol
+	b.SetChecksum(i.Checksum)
+	copy(b[srcAddr:srcAddr+IPv4AddressSize], i.SrcAddr)
+	copy(b[dstAddr:dstAddr+IPv4AddressSize], i.DstAddr)
+}
+
+// EncodePartial updates the total length and checksum fields of ipv4 header,
+// taking in the partial checksum, which is the checksum of the header without
+// the total length and checksum fields. It is useful in cases when similar
+// packets are produced.
+func (b IPv4) EncodePartial(partialChecksum, totalLength uint16) {
+	b.SetTotalLength(totalLength)
+	checksum := Checksum(b[totalLen:totalLen+2], partialChecksum)
+	b.SetChecksum(^checksum)
+}
+
+// IsValid performs basic validation on the packet.
+func (b IPv4) IsValid(pktSize int) bool {
+	if len(b) < IPv4MinimumSize {
+		return false
+	}
+
+	hlen := int(b.HeaderLength())
+	tlen := int(b.TotalLength())
+	if hlen > tlen || tlen > pktSize {
+		return false
+	}
+
+	return true
+}
diff --git a/pkg/tcpip/header/ipv6.go b/pkg/tcpip/header/ipv6.go
new file mode 100644
index 000000000..d8dc138b3
--- /dev/null
+++ b/pkg/tcpip/header/ipv6.go
@@ -0,0 +1,191 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	versTCFL   = 0
+	payloadLen = 4
+	nextHdr    = 6
+	hopLimit   = 7
+	v6SrcAddr  = 8
+	v6DstAddr  = 24
+)
+
+// IPv6Fields contains the fields of an IPv6 packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type IPv6Fields struct {
+	// TrafficClass is the "traffic class" field of an IPv6 packet.
+	TrafficClass uint8
+
+	// FlowLabel is the "flow label" field of an IPv6 packet.
+	FlowLabel uint32
+
+	// PayloadLength is the "payload length" field of an IPv6 packet.
+	PayloadLength uint16
+
+	// NextHeader is the "next header" field of an IPv6 packet.
+	NextHeader uint8
+
+	// HopLimit is the "hop limit" field of an IPv6 packet.
+	HopLimit uint8
+
+	// SrcAddr is the "source ip address" of an IPv6 packet.
+	SrcAddr tcpip.Address
+
+	// DstAddr is the "destination ip address" of an IPv6 packet.
+	DstAddr tcpip.Address
+}
+
+// IPv6 represents an ipv6 header stored in a byte array.
+// Most of the methods of IPv6 access to the underlying slice without
+// checking the boundaries and could panic because of 'index out of range'.
+// Always call IsValid() to validate an instance of IPv6 before using other methods.
+type IPv6 []byte
+
+const (
+	// IPv6MinimumSize is the minimum size of a valid IPv6 packet.
+	IPv6MinimumSize = 40
+
+	// IPv6AddressSize is the size, in bytes, of an IPv6 address.
+	IPv6AddressSize = 16
+
+	// IPv6ProtocolNumber is IPv6's network protocol number.
+	IPv6ProtocolNumber tcpip.NetworkProtocolNumber = 0x86dd
+
+	// IPv6Version is the version of the ipv6 procotol.
+	IPv6Version = 6
+
+	// IPv6MinimumMTU is the minimum MTU required by IPv6, per RFC 2460,
+	// section 5.
+	IPv6MinimumMTU = 1280
+)
+
+// PayloadLength returns the value of the "payload length" field of the ipv6
+// header.
+func (b IPv6) PayloadLength() uint16 {
+	return binary.BigEndian.Uint16(b[payloadLen:])
+}
+
+// HopLimit returns the value of the "hop limit" field of the ipv6 header.
+func (b IPv6) HopLimit() uint8 {
+	return b[hopLimit]
+}
+
+// NextHeader returns the value of the "next header" field of the ipv6 header.
+func (b IPv6) NextHeader() uint8 {
+	return b[nextHdr]
+}
+
+// TransportProtocol implements Network.TransportProtocol.
+func (b IPv6) TransportProtocol() tcpip.TransportProtocolNumber {
+	return tcpip.TransportProtocolNumber(b.NextHeader())
+}
+
+// Payload implements Network.Payload.
+func (b IPv6) Payload() []byte {
+	return b[IPv6MinimumSize:][:b.PayloadLength()]
+}
+
+// SourceAddress returns the "source address" field of the ipv6 header.
+func (b IPv6) SourceAddress() tcpip.Address {
+	return tcpip.Address(b[v6SrcAddr : v6SrcAddr+IPv6AddressSize])
+}
+
+// DestinationAddress returns the "destination address" field of the ipv6
+// header.
+func (b IPv6) DestinationAddress() tcpip.Address {
+	return tcpip.Address(b[v6DstAddr : v6DstAddr+IPv6AddressSize])
+}
+
+// Checksum implements Network.Checksum. Given that IPv6 doesn't have a
+// checksum, it just returns 0.
+func (IPv6) Checksum() uint16 {
+	return 0
+}
+
+// TOS returns the "traffic class" and "flow label" fields of the ipv6 header.
+func (b IPv6) TOS() (uint8, uint32) {
+	v := binary.BigEndian.Uint32(b[versTCFL:])
+	return uint8(v >> 20), v & 0xfffff
+}
+
+// SetTOS sets the "traffic class" and "flow label" fields of the ipv6 header.
+func (b IPv6) SetTOS(t uint8, l uint32) {
+	vtf := (6 << 28) | (uint32(t) << 20) | (l & 0xfffff)
+	binary.BigEndian.PutUint32(b[versTCFL:], vtf)
+}
+
+// SetPayloadLength sets the "payload length" field of the ipv6 header.
+func (b IPv6) SetPayloadLength(payloadLength uint16) {
+	binary.BigEndian.PutUint16(b[payloadLen:], payloadLength)
+}
+
+// SetSourceAddress sets the "source address" field of the ipv6 header.
+func (b IPv6) SetSourceAddress(addr tcpip.Address) {
+	copy(b[v6SrcAddr:v6SrcAddr+IPv6AddressSize], addr)
+}
+
+// SetDestinationAddress sets the "destination address" field of the ipv6
+// header.
+func (b IPv6) SetDestinationAddress(addr tcpip.Address) {
+	copy(b[v6DstAddr:v6DstAddr+IPv6AddressSize], addr)
+}
+
+// SetNextHeader sets the value of the "next header" field of the ipv6 header.
+func (b IPv6) SetNextHeader(v uint8) {
+	b[nextHdr] = v
+}
+
+// SetChecksum implements Network.SetChecksum. Given that IPv6 doesn't have a
+// checksum, it is empty.
+func (IPv6) SetChecksum(uint16) {
+}
+
+// Encode encodes all the fields of the ipv6 header.
+func (b IPv6) Encode(i *IPv6Fields) {
+	b.SetTOS(i.TrafficClass, i.FlowLabel)
+	b.SetPayloadLength(i.PayloadLength)
+	b[nextHdr] = i.NextHeader
+	b[hopLimit] = i.HopLimit
+	copy(b[v6SrcAddr:v6SrcAddr+IPv6AddressSize], i.SrcAddr)
+	copy(b[v6DstAddr:v6DstAddr+IPv6AddressSize], i.DstAddr)
+}
+
+// IsValid performs basic validation on the packet.
+func (b IPv6) IsValid(pktSize int) bool {
+	if len(b) < IPv6MinimumSize {
+		return false
+	}
+
+	dlen := int(b.PayloadLength())
+	if dlen > pktSize-IPv6MinimumSize {
+		return false
+	}
+
+	return true
+}
+
+// IsV4MappedAddress determines if the provided address is an IPv4 mapped
+// address by checking if its prefix is 0:0:0:0:0:ffff::/96.
+func IsV4MappedAddress(addr tcpip.Address) bool {
+	if len(addr) != IPv6AddressSize {
+		return false
+	}
+
+	const prefix = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff"
+	for i := 0; i < len(prefix); i++ {
+		if prefix[i] != addr[i] {
+			return false
+		}
+	}
+
+	return true
+}
diff --git a/pkg/tcpip/header/ipv6_fragment.go b/pkg/tcpip/header/ipv6_fragment.go
new file mode 100644
index 000000000..04aa5c7b8
--- /dev/null
+++ b/pkg/tcpip/header/ipv6_fragment.go
@@ -0,0 +1,136 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	nextHdrFrag = 0
+	fragOff     = 2
+	more        = 3
+	idV6        = 4
+)
+
+// IPv6FragmentFields contains the fields of an IPv6 fragment. It is used to describe the
+// fields of a packet that needs to be encoded.
+type IPv6FragmentFields struct {
+	// NextHeader is the "next header" field of an IPv6 fragment.
+	NextHeader uint8
+
+	// FragmentOffset is the "fragment offset" field of an IPv6 fragment.
+	FragmentOffset uint16
+
+	// M is the "more" field of an IPv6 fragment.
+	M bool
+
+	// Identification is the "identification" field of an IPv6 fragment.
+	Identification uint32
+}
+
+// IPv6Fragment represents an ipv6 fragment header stored in a byte array.
+// Most of the methods of IPv6Fragment access to the underlying slice without
+// checking the boundaries and could panic because of 'index out of range'.
+// Always call IsValid() to validate an instance of IPv6Fragment before using other methods.
+type IPv6Fragment []byte
+
+const (
+	// IPv6FragmentHeader header is the number used to specify that the next
+	// header is a fragment header, per RFC 2460.
+	IPv6FragmentHeader = 44
+
+	// IPv6FragmentHeaderSize is the size of the fragment header.
+	IPv6FragmentHeaderSize = 8
+)
+
+// Encode encodes all the fields of the ipv6 fragment.
+func (b IPv6Fragment) Encode(i *IPv6FragmentFields) {
+	b[nextHdrFrag] = i.NextHeader
+	binary.BigEndian.PutUint16(b[fragOff:], i.FragmentOffset<<3)
+	if i.M {
+		b[more] |= 1
+	}
+	binary.BigEndian.PutUint32(b[idV6:], i.Identification)
+}
+
+// IsValid performs basic validation on the fragment header.
+func (b IPv6Fragment) IsValid() bool {
+	return len(b) >= IPv6FragmentHeaderSize
+}
+
+// NextHeader returns the value of the "next header" field of the ipv6 fragment.
+func (b IPv6Fragment) NextHeader() uint8 {
+	return b[nextHdrFrag]
+}
+
+// FragmentOffset returns the "fragment offset" field of the ipv6 fragment.
+func (b IPv6Fragment) FragmentOffset() uint16 {
+	return binary.BigEndian.Uint16(b[fragOff:]) >> 3
+}
+
+// More returns the "more" field of the ipv6 fragment.
+func (b IPv6Fragment) More() bool {
+	return b[more]&1 > 0
+}
+
+// Payload implements Network.Payload.
+func (b IPv6Fragment) Payload() []byte {
+	return b[IPv6FragmentHeaderSize:]
+}
+
+// ID returns the value of the identifier field of the ipv6 fragment.
+func (b IPv6Fragment) ID() uint32 {
+	return binary.BigEndian.Uint32(b[idV6:])
+}
+
+// TransportProtocol implements Network.TransportProtocol.
+func (b IPv6Fragment) TransportProtocol() tcpip.TransportProtocolNumber {
+	return tcpip.TransportProtocolNumber(b.NextHeader())
+}
+
+// The functions below have been added only to satisfy the Network interface.
+
+// Checksum is not supported by IPv6Fragment.
+func (b IPv6Fragment) Checksum() uint16 {
+	panic("not supported")
+}
+
+// SourceAddress is not supported by IPv6Fragment.
+func (b IPv6Fragment) SourceAddress() tcpip.Address {
+	panic("not supported")
+}
+
+// DestinationAddress is not supported by IPv6Fragment.
+func (b IPv6Fragment) DestinationAddress() tcpip.Address {
+	panic("not supported")
+}
+
+// SetSourceAddress is not supported by IPv6Fragment.
+func (b IPv6Fragment) SetSourceAddress(tcpip.Address) {
+	panic("not supported")
+}
+
+// SetDestinationAddress is not supported by IPv6Fragment.
+func (b IPv6Fragment) SetDestinationAddress(tcpip.Address) {
+	panic("not supported")
+}
+
+// SetChecksum is not supported by IPv6Fragment.
+func (b IPv6Fragment) SetChecksum(uint16) {
+	panic("not supported")
+}
+
+// TOS is not supported by IPv6Fragment.
+func (b IPv6Fragment) TOS() (uint8, uint32) {
+	panic("not supported")
+}
+
+// SetTOS is not supported by IPv6Fragment.
+func (b IPv6Fragment) SetTOS(t uint8, l uint32) {
+	panic("not supported")
+}
diff --git a/pkg/tcpip/header/ipversion_test.go b/pkg/tcpip/header/ipversion_test.go
new file mode 100644
index 000000000..5f3956160
--- /dev/null
+++ b/pkg/tcpip/header/ipversion_test.go
@@ -0,0 +1,57 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header_test
+
+import (
+	"testing"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+)
+
+func TestIPv4(t *testing.T) {
+	b := header.IPv4(make([]byte, header.IPv4MinimumSize))
+	b.Encode(&header.IPv4Fields{})
+
+	const want = header.IPv4Version
+	if v := header.IPVersion(b); v != want {
+		t.Fatalf("Bad version, want %v, got %v", want, v)
+	}
+}
+
+func TestIPv6(t *testing.T) {
+	b := header.IPv6(make([]byte, header.IPv6MinimumSize))
+	b.Encode(&header.IPv6Fields{})
+
+	const want = header.IPv6Version
+	if v := header.IPVersion(b); v != want {
+		t.Fatalf("Bad version, want %v, got %v", want, v)
+	}
+}
+
+func TestOtherVersion(t *testing.T) {
+	const want = header.IPv4Version + header.IPv6Version
+	b := make([]byte, 1)
+	b[0] = want << 4
+
+	if v := header.IPVersion(b); v != want {
+		t.Fatalf("Bad version, want %v, got %v", want, v)
+	}
+}
+
+func TestTooShort(t *testing.T) {
+	b := make([]byte, 1)
+	b[0] = (header.IPv4Version + header.IPv6Version) << 4
+
+	// Get the version of a zero-length slice.
+	const want = -1
+	if v := header.IPVersion(b[:0]); v != want {
+		t.Fatalf("Bad version, want %v, got %v", want, v)
+	}
+
+	// Get the version of a nil slice.
+	if v := header.IPVersion(nil); v != want {
+		t.Fatalf("Bad version, want %v, got %v", want, v)
+	}
+}
diff --git a/pkg/tcpip/header/tcp.go b/pkg/tcpip/header/tcp.go
new file mode 100644
index 000000000..995df4076
--- /dev/null
+++ b/pkg/tcpip/header/tcp.go
@@ -0,0 +1,518 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/seqnum"
+)
+
+const (
+	srcPort     = 0
+	dstPort     = 2
+	seqNum      = 4
+	ackNum      = 8
+	dataOffset  = 12
+	tcpFlags    = 13
+	winSize     = 14
+	tcpChecksum = 16
+	urgentPtr   = 18
+)
+
+const (
+	// MaxWndScale is maximum allowed window scaling, as described in
+	// RFC 1323, section 2.3, page 11.
+	MaxWndScale = 14
+
+	// TCPMaxSACKBlocks is the maximum number of SACK blocks that can
+	// be encoded in a TCP option field.
+	TCPMaxSACKBlocks = 4
+)
+
+// Flags that may be set in a TCP segment.
+const (
+	TCPFlagFin = 1 << iota
+	TCPFlagSyn
+	TCPFlagRst
+	TCPFlagPsh
+	TCPFlagAck
+	TCPFlagUrg
+)
+
+// Options that may be present in a TCP segment.
+const (
+	TCPOptionEOL           = 0
+	TCPOptionNOP           = 1
+	TCPOptionMSS           = 2
+	TCPOptionWS            = 3
+	TCPOptionTS            = 8
+	TCPOptionSACKPermitted = 4
+	TCPOptionSACK          = 5
+)
+
+// TCPFields contains the fields of a TCP packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type TCPFields struct {
+	// SrcPort is the "source port" field of a TCP packet.
+	SrcPort uint16
+
+	// DstPort is the "destination port" field of a TCP packet.
+	DstPort uint16
+
+	// SeqNum is the "sequence number" field of a TCP packet.
+	SeqNum uint32
+
+	// AckNum is the "acknowledgement number" field of a TCP packet.
+	AckNum uint32
+
+	// DataOffset is the "data offset" field of a TCP packet.
+	DataOffset uint8
+
+	// Flags is the "flags" field of a TCP packet.
+	Flags uint8
+
+	// WindowSize is the "window size" field of a TCP packet.
+	WindowSize uint16
+
+	// Checksum is the "checksum" field of a TCP packet.
+	Checksum uint16
+
+	// UrgentPointer is the "urgent pointer" field of a TCP packet.
+	UrgentPointer uint16
+}
+
+// TCPSynOptions is used to return the parsed TCP Options in a syn
+// segment.
+type TCPSynOptions struct {
+	// MSS is the maximum segment size provided by the peer in the SYN.
+	MSS uint16
+
+	// WS is the window scale option provided by the peer in the SYN.
+	//
+	// Set to -1 if no window scale option was provided.
+	WS int
+
+	// TS is true if the timestamp option was provided in the syn/syn-ack.
+	TS bool
+
+	// TSVal is the value of the TSVal field in the timestamp option.
+	TSVal uint32
+
+	// TSEcr is the value of the TSEcr field in the timestamp option.
+	TSEcr uint32
+
+	// SACKPermitted is true if the SACK option was provided in the SYN/SYN-ACK.
+	SACKPermitted bool
+}
+
+// SACKBlock represents a single contiguous SACK block.
+type SACKBlock struct {
+	// Start indicates the lowest sequence number in the block.
+	Start seqnum.Value
+
+	// End indicates the sequence number immediately following the last
+	// sequence number of this block.
+	End seqnum.Value
+}
+
+// TCPOptions are used to parse and cache the TCP segment options for a non
+// syn/syn-ack segment.
+type TCPOptions struct {
+	// TS is true if the TimeStamp option is enabled.
+	TS bool
+
+	// TSVal is the value in the TSVal field of the segment.
+	TSVal uint32
+
+	// TSEcr is the value in the TSEcr field of the segment.
+	TSEcr uint32
+
+	// SACKBlocks are the SACK blocks specified in the segment.
+	SACKBlocks []SACKBlock
+}
+
+// TCP represents a TCP header stored in a byte array.
+type TCP []byte
+
+const (
+	// TCPMinimumSize is the minimum size of a valid TCP packet.
+	TCPMinimumSize = 20
+
+	// TCPProtocolNumber is TCP's transport protocol number.
+	TCPProtocolNumber tcpip.TransportProtocolNumber = 6
+)
+
+// SourcePort returns the "source port" field of the tcp header.
+func (b TCP) SourcePort() uint16 {
+	return binary.BigEndian.Uint16(b[srcPort:])
+}
+
+// DestinationPort returns the "destination port" field of the tcp header.
+func (b TCP) DestinationPort() uint16 {
+	return binary.BigEndian.Uint16(b[dstPort:])
+}
+
+// SequenceNumber returns the "sequence number" field of the tcp header.
+func (b TCP) SequenceNumber() uint32 {
+	return binary.BigEndian.Uint32(b[seqNum:])
+}
+
+// AckNumber returns the "ack number" field of the tcp header.
+func (b TCP) AckNumber() uint32 {
+	return binary.BigEndian.Uint32(b[ackNum:])
+}
+
+// DataOffset returns the "data offset" field of the tcp header.
+func (b TCP) DataOffset() uint8 {
+	return (b[dataOffset] >> 4) * 4
+}
+
+// Payload returns the data in the tcp packet.
+func (b TCP) Payload() []byte {
+	return b[b.DataOffset():]
+}
+
+// Flags returns the flags field of the tcp header.
+func (b TCP) Flags() uint8 {
+	return b[tcpFlags]
+}
+
+// WindowSize returns the "window size" field of the tcp header.
+func (b TCP) WindowSize() uint16 {
+	return binary.BigEndian.Uint16(b[winSize:])
+}
+
+// Checksum returns the "checksum" field of the tcp header.
+func (b TCP) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[tcpChecksum:])
+}
+
+// SetSourcePort sets the "source port" field of the tcp header.
+func (b TCP) SetSourcePort(port uint16) {
+	binary.BigEndian.PutUint16(b[srcPort:], port)
+}
+
+// SetDestinationPort sets the "destination port" field of the tcp header.
+func (b TCP) SetDestinationPort(port uint16) {
+	binary.BigEndian.PutUint16(b[dstPort:], port)
+}
+
+// SetChecksum sets the checksum field of the tcp header.
+func (b TCP) SetChecksum(checksum uint16) {
+	binary.BigEndian.PutUint16(b[tcpChecksum:], checksum)
+}
+
+// CalculateChecksum calculates the checksum of the tcp segment given
+// the totalLen and partialChecksum(descriptions below)
+// totalLen is the total length of the segment
+// partialChecksum is the checksum of the network-layer pseudo-header
+// (excluding the total length) and the checksum of the segment data.
+func (b TCP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16 {
+	// Add the length portion of the checksum to the pseudo-checksum.
+	tmp := make([]byte, 2)
+	binary.BigEndian.PutUint16(tmp, totalLen)
+	checksum := Checksum(tmp, partialChecksum)
+
+	// Calculate the rest of the checksum.
+	return Checksum(b[:b.DataOffset()], checksum)
+}
+
+// Options returns a slice that holds the unparsed TCP options in the segment.
+func (b TCP) Options() []byte {
+	return b[TCPMinimumSize:b.DataOffset()]
+}
+
+// ParsedOptions returns a TCPOptions structure which parses and caches the TCP
+// option values in the TCP segment. NOTE: Invoking this function repeatedly is
+// expensive as it reparses the options on each invocation.
+func (b TCP) ParsedOptions() TCPOptions {
+	return ParseTCPOptions(b.Options())
+}
+
+func (b TCP) encodeSubset(seq, ack uint32, flags uint8, rcvwnd uint16) {
+	binary.BigEndian.PutUint32(b[seqNum:], seq)
+	binary.BigEndian.PutUint32(b[ackNum:], ack)
+	b[tcpFlags] = flags
+	binary.BigEndian.PutUint16(b[winSize:], rcvwnd)
+}
+
+// Encode encodes all the fields of the tcp header.
+func (b TCP) Encode(t *TCPFields) {
+	b.encodeSubset(t.SeqNum, t.AckNum, t.Flags, t.WindowSize)
+	binary.BigEndian.PutUint16(b[srcPort:], t.SrcPort)
+	binary.BigEndian.PutUint16(b[dstPort:], t.DstPort)
+	b[dataOffset] = (t.DataOffset / 4) << 4
+	binary.BigEndian.PutUint16(b[tcpChecksum:], t.Checksum)
+	binary.BigEndian.PutUint16(b[urgentPtr:], t.UrgentPointer)
+}
+
+// EncodePartial updates a subset of the fields of the tcp header. It is useful
+// in cases when similar segments are produced.
+func (b TCP) EncodePartial(partialChecksum, length uint16, seqnum, acknum uint32, flags byte, rcvwnd uint16) {
+	// Add the total length and "flags" field contributions to the checksum.
+	// We don't use the flags field directly from the header because it's a
+	// one-byte field with an odd offset, so it would be accounted for
+	// incorrectly by the Checksum routine.
+	tmp := make([]byte, 4)
+	binary.BigEndian.PutUint16(tmp, length)
+	binary.BigEndian.PutUint16(tmp[2:], uint16(flags))
+	checksum := Checksum(tmp, partialChecksum)
+
+	// Encode the passed-in fields.
+	b.encodeSubset(seqnum, acknum, flags, rcvwnd)
+
+	// Add the contributions of the passed-in fields to the checksum.
+	checksum = Checksum(b[seqNum:seqNum+8], checksum)
+	checksum = Checksum(b[winSize:winSize+2], checksum)
+
+	// Encode the checksum.
+	b.SetChecksum(^checksum)
+}
+
+// ParseSynOptions parses the options received in a SYN segment and returns the
+// relevant ones. opts should point to the option part of the TCP Header.
+func ParseSynOptions(opts []byte, isAck bool) TCPSynOptions {
+	limit := len(opts)
+
+	synOpts := TCPSynOptions{
+		// Per RFC 1122, page 85: "If an MSS option is not received at
+		// connection setup, TCP MUST assume a default send MSS of 536."
+		MSS: 536,
+		// If no window scale option is specified, WS in options is
+		// returned as -1; this is because the absence of the option
+		// indicates that the we cannot use window scaling on the
+		// receive end either.
+		WS: -1,
+	}
+
+	for i := 0; i < limit; {
+		switch opts[i] {
+		case TCPOptionEOL:
+			i = limit
+		case TCPOptionNOP:
+			i++
+		case TCPOptionMSS:
+			if i+4 > limit || opts[i+1] != 4 {
+				return synOpts
+			}
+			mss := uint16(opts[i+2])<<8 | uint16(opts[i+3])
+			if mss == 0 {
+				return synOpts
+			}
+			synOpts.MSS = mss
+			i += 4
+
+		case TCPOptionWS:
+			if i+3 > limit || opts[i+1] != 3 {
+				return synOpts
+			}
+			ws := int(opts[i+2])
+			if ws > MaxWndScale {
+				ws = MaxWndScale
+			}
+			synOpts.WS = ws
+			i += 3
+
+		case TCPOptionTS:
+			if i+10 > limit || opts[i+1] != 10 {
+				return synOpts
+			}
+			synOpts.TSVal = binary.BigEndian.Uint32(opts[i+2:])
+			if isAck {
+				// If the segment is a SYN-ACK then store the Timestamp Echo Reply
+				// in the segment.
+				synOpts.TSEcr = binary.BigEndian.Uint32(opts[i+6:])
+			}
+			synOpts.TS = true
+			i += 10
+		case TCPOptionSACKPermitted:
+			if i+2 > limit || opts[i+1] != 2 {
+				return synOpts
+			}
+			synOpts.SACKPermitted = true
+			i += 2
+
+		default:
+			// We don't recognize this option, just skip over it.
+			if i+2 > limit {
+				return synOpts
+			}
+			l := int(opts[i+1])
+			// If the length is incorrect or if l+i overflows the
+			// total options length then return false.
+			if l < 2 || i+l > limit {
+				return synOpts
+			}
+			i += l
+		}
+	}
+
+	return synOpts
+}
+
+// ParseTCPOptions extracts and stores all known options in the provided byte
+// slice in a TCPOptions structure.
+func ParseTCPOptions(b []byte) TCPOptions {
+	opts := TCPOptions{}
+	limit := len(b)
+	for i := 0; i < limit; {
+		switch b[i] {
+		case TCPOptionEOL:
+			i = limit
+		case TCPOptionNOP:
+			i++
+		case TCPOptionTS:
+			if i+10 > limit || (b[i+1] != 10) {
+				return opts
+			}
+			opts.TS = true
+			opts.TSVal = binary.BigEndian.Uint32(b[i+2:])
+			opts.TSEcr = binary.BigEndian.Uint32(b[i+6:])
+			i += 10
+		case TCPOptionSACK:
+			if i+2 > limit {
+				// Malformed SACK block, just return and stop parsing.
+				return opts
+			}
+			sackOptionLen := int(b[i+1])
+			if i+sackOptionLen > limit || (sackOptionLen-2)%8 != 0 {
+				// Malformed SACK block, just return and stop parsing.
+				return opts
+			}
+			numBlocks := (sackOptionLen - 2) / 8
+			opts.SACKBlocks = []SACKBlock{}
+			for j := 0; j < numBlocks; j++ {
+				start := binary.BigEndian.Uint32(b[i+2+j*8:])
+				end := binary.BigEndian.Uint32(b[i+2+j*8+4:])
+				opts.SACKBlocks = append(opts.SACKBlocks, SACKBlock{
+					Start: seqnum.Value(start),
+					End:   seqnum.Value(end),
+				})
+			}
+			i += sackOptionLen
+		default:
+			// We don't recognize this option, just skip over it.
+			if i+2 > limit {
+				return opts
+			}
+			l := int(b[i+1])
+			// If the length is incorrect or if l+i overflows the
+			// total options length then return false.
+			if l < 2 || i+l > limit {
+				return opts
+			}
+			i += l
+		}
+	}
+	return opts
+}
+
+// EncodeMSSOption encodes the MSS TCP option with the provided MSS values in
+// the supplied buffer. If the provided buffer is not large enough then it just
+// returns without encoding anything. It returns the number of bytes written to
+// the provided buffer.
+func EncodeMSSOption(mss uint32, b []byte) int {
+	// mssOptionSize is the number of bytes in a valid MSS option.
+	const mssOptionSize = 4
+
+	if len(b) < mssOptionSize {
+		return 0
+	}
+	b[0], b[1], b[2], b[3] = TCPOptionMSS, mssOptionSize, byte(mss>>8), byte(mss)
+	return mssOptionSize
+}
+
+// EncodeWSOption encodes the WS TCP option with the WS value in the
+// provided buffer. If the provided buffer is not large enough then it just
+// returns without encoding anything. It returns the number of bytes written to
+// the provided buffer.
+func EncodeWSOption(ws int, b []byte) int {
+	if len(b) < 3 {
+		return 0
+	}
+	b[0], b[1], b[2] = TCPOptionWS, 3, uint8(ws)
+	return int(b[1])
+}
+
+// EncodeTSOption encodes the provided tsVal and tsEcr values as a TCP timestamp
+// option into the provided buffer. If the buffer is smaller than expected it
+// just returns without encoding anything. It returns the number of bytes
+// written to the provided buffer.
+func EncodeTSOption(tsVal, tsEcr uint32, b []byte) int {
+	if len(b) < 10 {
+		return 0
+	}
+	b[0], b[1] = TCPOptionTS, 10
+	binary.BigEndian.PutUint32(b[2:], tsVal)
+	binary.BigEndian.PutUint32(b[6:], tsEcr)
+	return int(b[1])
+}
+
+// EncodeSACKPermittedOption encodes a SACKPermitted option into the provided
+// buffer. If the buffer is smaller than required it just returns without
+// encoding anything. It returns the number of bytes written to the provided
+// buffer.
+func EncodeSACKPermittedOption(b []byte) int {
+	if len(b) < 2 {
+		return 0
+	}
+
+	b[0], b[1] = TCPOptionSACKPermitted, 2
+	return int(b[1])
+}
+
+// EncodeSACKBlocks encodes the provided SACK blocks as a TCP SACK option block
+// in the provided slice. It tries to fit in as many blocks as possible based on
+// number of bytes available in the provided buffer. It returns the number of
+// bytes written to the provided buffer.
+func EncodeSACKBlocks(sackBlocks []SACKBlock, b []byte) int {
+	if len(sackBlocks) == 0 {
+		return 0
+	}
+	l := len(sackBlocks)
+	if l > TCPMaxSACKBlocks {
+		l = TCPMaxSACKBlocks
+	}
+	if ll := (len(b) - 2) / 8; ll < l {
+		l = ll
+	}
+	if l == 0 {
+		// There is not enough space in the provided buffer to add
+		// any SACK blocks.
+		return 0
+	}
+	b[0] = TCPOptionSACK
+	b[1] = byte(l*8 + 2)
+	for i := 0; i < l; i++ {
+		binary.BigEndian.PutUint32(b[i*8+2:], uint32(sackBlocks[i].Start))
+		binary.BigEndian.PutUint32(b[i*8+6:], uint32(sackBlocks[i].End))
+	}
+	return int(b[1])
+}
+
+// EncodeNOP adds an explicit NOP to the option list.
+func EncodeNOP(b []byte) int {
+	if len(b) == 0 {
+		return 0
+	}
+	b[0] = TCPOptionNOP
+	return 1
+}
+
+// AddTCPOptionPadding adds the required number of TCPOptionNOP to quad align
+// the option buffer. It adds padding bytes after the offset specified and
+// returns the number of padding bytes added. The passed in options slice
+// must have space for the padding bytes.
+func AddTCPOptionPadding(options []byte, offset int) int {
+	paddingToAdd := -offset & 3
+	// Now add any padding bytes that might be required to quad align the
+	// options.
+	for i := offset; i < offset+paddingToAdd; i++ {
+		options[i] = TCPOptionNOP
+	}
+	return paddingToAdd
+}
diff --git a/pkg/tcpip/header/tcp_test.go b/pkg/tcpip/header/tcp_test.go
new file mode 100644
index 000000000..27d43479a
--- /dev/null
+++ b/pkg/tcpip/header/tcp_test.go
@@ -0,0 +1,134 @@
+package header_test
+
+import (
+	"reflect"
+	"testing"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
+)
+
+func TestEncodeSACKBlocks(t *testing.T) {
+	testCases := []struct {
+		sackBlocks []header.SACKBlock
+		want       []header.SACKBlock
+		bufSize    int
+	}{
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}},
+			40,
+		},
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}},
+			30,
+		},
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			[]header.SACKBlock{{10, 20}, {22, 30}},
+			20,
+		},
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			[]header.SACKBlock{{10, 20}},
+			10,
+		},
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			nil,
+			8,
+		},
+		{
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}, {52, 60}, {62, 70}},
+			[]header.SACKBlock{{10, 20}, {22, 30}, {32, 40}, {42, 50}},
+			60,
+		},
+	}
+	for _, tc := range testCases {
+		b := make([]byte, tc.bufSize)
+		t.Logf("testing: %v", tc)
+		header.EncodeSACKBlocks(tc.sackBlocks, b)
+		opts := header.ParseTCPOptions(b)
+		if got, want := opts.SACKBlocks, tc.want; !reflect.DeepEqual(got, want) {
+			t.Errorf("header.EncodeSACKBlocks(%v, %v), encoded blocks got: %v, want: %v", tc.sackBlocks, b, got, want)
+		}
+	}
+}
+
+func TestTCPParseOptions(t *testing.T) {
+	type tsOption struct {
+		tsVal uint32
+		tsEcr uint32
+	}
+
+	generateOptions := func(tsOpt *tsOption, sackBlocks []header.SACKBlock) []byte {
+		l := 0
+		if tsOpt != nil {
+			l += 10
+		}
+		if len(sackBlocks) != 0 {
+			l += len(sackBlocks)*8 + 2
+		}
+		b := make([]byte, l)
+		offset := 0
+		if tsOpt != nil {
+			offset = header.EncodeTSOption(tsOpt.tsVal, tsOpt.tsEcr, b)
+		}
+		header.EncodeSACKBlocks(sackBlocks, b[offset:])
+		return b
+	}
+
+	testCases := []struct {
+		b    []byte
+		want header.TCPOptions
+	}{
+		// Trivial cases.
+		{nil, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionNOP}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionNOP, header.TCPOptionNOP}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionEOL}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionNOP, header.TCPOptionEOL, header.TCPOptionTS, 10, 1, 1}, header.TCPOptions{false, 0, 0, nil}},
+
+		// Test timestamp parsing.
+		{[]byte{header.TCPOptionNOP, header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{true, 1, 1, nil}},
+		{[]byte{header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{true, 1, 1, nil}},
+
+		// Test malformed timestamp option.
+		{[]byte{header.TCPOptionTS, 8, 1, 1}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionNOP, header.TCPOptionTS, 8, 1, 1}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionNOP, header.TCPOptionTS, 8, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{false, 0, 0, nil}},
+
+		// Test SACKBlock parsing.
+		{[]byte{header.TCPOptionSACK, 10, 0, 0, 0, 1, 0, 0, 0, 10}, header.TCPOptions{false, 0, 0, []header.SACKBlock{{1, 10}}}},
+		{[]byte{header.TCPOptionSACK, 18, 0, 0, 0, 1, 0, 0, 0, 10, 0, 0, 0, 11, 0, 0, 0, 12}, header.TCPOptions{false, 0, 0, []header.SACKBlock{{1, 10}, {11, 12}}}},
+
+		// Test malformed SACK option.
+		{[]byte{header.TCPOptionSACK, 0}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 8, 0, 0, 0, 1, 0, 0, 0, 10}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 11, 0, 0, 0, 1, 0, 0, 0, 10, 0, 0, 0, 11, 0, 0, 0, 12}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 17, 0, 0, 0, 1, 0, 0, 0, 10, 0, 0, 0, 11, 0, 0, 0, 12}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 10}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 10, 0, 0, 0, 1, 0, 0, 0}, header.TCPOptions{false, 0, 0, nil}},
+
+		// Test Timestamp + SACK block parsing.
+		{generateOptions(&tsOption{1, 1}, []header.SACKBlock{{1, 10}, {11, 12}}), header.TCPOptions{true, 1, 1, []header.SACKBlock{{1, 10}, {11, 12}}}},
+		{generateOptions(&tsOption{1, 2}, []header.SACKBlock{{1, 10}, {11, 12}}), header.TCPOptions{true, 1, 2, []header.SACKBlock{{1, 10}, {11, 12}}}},
+		{generateOptions(&tsOption{1, 3}, []header.SACKBlock{{1, 10}, {11, 12}, {13, 14}, {14, 15}, {15, 16}}), header.TCPOptions{true, 1, 3, []header.SACKBlock{{1, 10}, {11, 12}, {13, 14}, {14, 15}}}},
+
+		// Test valid timestamp + malformed SACK block parsing.
+		{[]byte{header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1, header.TCPOptionSACK}, header.TCPOptions{true, 1, 1, nil}},
+		{[]byte{header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1, header.TCPOptionSACK, 10}, header.TCPOptions{true, 1, 1, nil}},
+		{[]byte{header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1, header.TCPOptionSACK, 10, 0, 0, 0}, header.TCPOptions{true, 1, 1, nil}},
+		{[]byte{header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1, header.TCPOptionSACK, 11, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{true, 1, 1, nil}},
+		{[]byte{header.TCPOptionSACK, header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{false, 0, 0, nil}},
+		{[]byte{header.TCPOptionSACK, 10, header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{false, 0, 0, []header.SACKBlock{{134873088, 65536}}}},
+		{[]byte{header.TCPOptionSACK, 10, 0, 0, 0, header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{false, 0, 0, []header.SACKBlock{{8, 167772160}}}},
+		{[]byte{header.TCPOptionSACK, 11, 0, 0, 0, 1, 0, 0, 0, 1, header.TCPOptionTS, 10, 0, 0, 0, 1, 0, 0, 0, 1}, header.TCPOptions{false, 0, 0, nil}},
+	}
+	for _, tc := range testCases {
+		if got, want := header.ParseTCPOptions(tc.b), tc.want; !reflect.DeepEqual(got, want) {
+			t.Errorf("ParseTCPOptions(%v) = %v, want: %v", tc.b, got, tc.want)
+		}
+	}
+}
diff --git a/pkg/tcpip/header/udp.go b/pkg/tcpip/header/udp.go
new file mode 100644
index 000000000..7c2548634
--- /dev/null
+++ b/pkg/tcpip/header/udp.go
@@ -0,0 +1,106 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	udpSrcPort  = 0
+	udpDstPort  = 2
+	udpLength   = 4
+	udpChecksum = 6
+)
+
+// UDPFields contains the fields of a UDP packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type UDPFields struct {
+	// SrcPort is the "source port" field of a UDP packet.
+	SrcPort uint16
+
+	// DstPort is the "destination port" field of a UDP packet.
+	DstPort uint16
+
+	// Length is the "length" field of a UDP packet.
+	Length uint16
+
+	// Checksum is the "checksum" field of a UDP packet.
+	Checksum uint16
+}
+
+// UDP represents a UDP header stored in a byte array.
+type UDP []byte
+
+const (
+	// UDPMinimumSize is the minimum size of a valid UDP packet.
+	UDPMinimumSize = 8
+
+	// UDPProtocolNumber is UDP's transport protocol number.
+	UDPProtocolNumber tcpip.TransportProtocolNumber = 17
+)
+
+// SourcePort returns the "source port" field of the udp header.
+func (b UDP) SourcePort() uint16 {
+	return binary.BigEndian.Uint16(b[udpSrcPort:])
+}
+
+// DestinationPort returns the "destination port" field of the udp header.
+func (b UDP) DestinationPort() uint16 {
+	return binary.BigEndian.Uint16(b[udpDstPort:])
+}
+
+// Length returns the "length" field of the udp header.
+func (b UDP) Length() uint16 {
+	return binary.BigEndian.Uint16(b[udpLength:])
+}
+
+// Payload returns the data contained in the UDP datagram.
+func (b UDP) Payload() []byte {
+	return b[UDPMinimumSize:]
+}
+
+// Checksum returns the "checksum" field of the udp header.
+func (b UDP) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[udpChecksum:])
+}
+
+// SetSourcePort sets the "source port" field of the udp header.
+func (b UDP) SetSourcePort(port uint16) {
+	binary.BigEndian.PutUint16(b[udpSrcPort:], port)
+}
+
+// SetDestinationPort sets the "destination port" field of the udp header.
+func (b UDP) SetDestinationPort(port uint16) {
+	binary.BigEndian.PutUint16(b[udpDstPort:], port)
+}
+
+// SetChecksum sets the "checksum" field of the udp header.
+func (b UDP) SetChecksum(checksum uint16) {
+	binary.BigEndian.PutUint16(b[udpChecksum:], checksum)
+}
+
+// CalculateChecksum calculates the checksum of the udp packet, given the total
+// length of the packet and the checksum of the network-layer pseudo-header
+// (excluding the total length) and the checksum of the payload.
+func (b UDP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16 {
+	// Add the length portion of the checksum to the pseudo-checksum.
+	tmp := make([]byte, 2)
+	binary.BigEndian.PutUint16(tmp, totalLen)
+	checksum := Checksum(tmp, partialChecksum)
+
+	// Calculate the rest of the checksum.
+	return Checksum(b[:UDPMinimumSize], checksum)
+}
+
+// Encode encodes all the fields of the udp header.
+func (b UDP) Encode(u *UDPFields) {
+	binary.BigEndian.PutUint16(b[udpSrcPort:], u.SrcPort)
+	binary.BigEndian.PutUint16(b[udpDstPort:], u.DstPort)
+	binary.BigEndian.PutUint16(b[udpLength:], u.Length)
+	binary.BigEndian.PutUint16(b[udpChecksum:], u.Checksum)
+}