Table of Contents

Class IpV4Packet

Namespace
VpnHood.Net.Packets
Assembly
VpnHood.Net.Packets.dll

Represents an IPv4 packet (RFC 791) over a buffer, which it reads and writes in place.

public class IpV4Packet : IpPacket, IDisposable
Inheritance
IpV4Packet
Implements
Inherited Members

Remarks

The PacketMemory a packet is made on says whether the packet owns its memory. Changing a header field does not update the header checksum: call UpdateHeaderChecksum() or UpdateAllChecksums(IpPacket) before sending.

Constructors

IpV4Packet(PacketMemory)

Initializes a new instance of the IpV4Packet class by parsing the packet at the start of some memory.

public IpV4Packet(PacketMemory memory)

Parameters

memory PacketMemory

The memory, which holds the packet from its first byte and may be longer: a Memory<T> or an array the caller keeps, or memory given to the packet (see PacketMemory), which stays the caller's when parsing fails.

Remarks

The packet takes the memory's first total-length bytes and leaves the rest. It checks the header's version and lengths, not its checksum.

Exceptions

ArgumentException

The bytes are no IPv4 packet, their header length or total length is invalid, or the memory is shorter than the packet.

IndexOutOfRangeException

memory is empty.

IpV4Packet(PacketMemory, int, IpProtocol, int)

Initializes a new instance of the IpV4Packet class by building a new packet at the start of some memory.

public IpV4Packet(PacketMemory memory, int packetLength, IpProtocol protocol, int optionsLength)

Parameters

memory PacketMemory

The memory, at least packetLength bytes: a Memory<T> or an array the caller keeps, or memory given to the packet (see PacketMemory), which stays the caller's when building fails.

packetLength int

The packet's total length in bytes, from 20 to 65535, and at least 20 plus optionsLength.

protocol IpProtocol

The protocol of the payload.

optionsLength int

The length of the header options, a multiple of 4 from 0 to 40.

Remarks

The packet's bytes are cleared, then the version, the header length, the protocol and the total length are written. The addresses, the time to live and the checksum are left zero. A build that is refused writes nothing.

Exceptions

ArgumentException

packetLength is below 20, above 65535, or shorter than the header with its options.

ArgumentOutOfRangeException

optionsLength is out of range or not a multiple of 4, or packetLength is negative or exceeds the memory.

Properties

DontFragment

Gets or sets a value indicating whether routers may not fragment the packet.

public bool DontFragment { get; set; }

Property Value

bool

Dscp

Gets or sets the Differentiated Services Code Point, the high 6 bits of the type-of-service byte.

public byte Dscp { get; set; }

Property Value

byte

Remarks

A value is masked to its low 6 bits.

Ecn

Gets or sets the Explicit Congestion Notification codepoint, the low 2 bits of the type-of-service byte.

public IpEcnField Ecn { get; set; }

Property Value

IpEcnField

FragmentFlags

Gets or sets the 3 flag bits: reserved, Don't Fragment and More Fragments, from the highest.

public byte FragmentFlags { get; set; }

Property Value

byte

FragmentOffset

Gets or sets the fragment's place in the datagram, in units of 8 bytes, from 0 to 8191.

public int FragmentOffset { get; set; }

Property Value

int

Remarks

A value is masked to its low 13 bits, so a larger one wraps.

Header

Gets the bytes before the upper layer: the IP header with its options, and IPv6's extension headers.

public override Memory<byte> Header { get; }

Property Value

Memory<byte>

HeaderChecksum

Gets or sets the header checksum field as it is in the header.

public ushort HeaderChecksum { get; set; }

Property Value

ushort

Identification

Gets or sets the identification, which the fragments of one datagram share.

public ushort Identification { get; set; }

Property Value

ushort

InternetHeaderLength

Gets the header length in 32-bit words, from 5 to 15.

public int InternetHeaderLength { get; }

Property Value

int

IsFragment

Gets a value indicating whether the packet is a fragment: More Fragments is set, or the fragment offset is not zero.

public override bool IsFragment { get; }

Property Value

bool

MoreFragments

Gets or sets a value indicating whether more fragments of the datagram follow this one.

public bool MoreFragments { get; set; }

Property Value

bool

Options

Gets the header options: the bytes between the 20-byte fixed header and the payload.

public Memory<byte> Options { get; }

Property Value

Memory<byte>

Protocol

Gets the protocol of the upper layer the payload carries, such as TCP.

public override IpProtocol Protocol { get; }

Property Value

IpProtocol

Remarks

An IPv6 packet reads through its extension headers to the upper layer; when it stops at one it does not read through, it names that header instead (see HasUnreadExtensionHeader).

TimeToLive

Gets or sets the time to live: the number of hops the packet may still take.

public override byte TimeToLive { get; set; }

Property Value

byte

TypeOfService

Gets or sets the whole type-of-service byte, which holds Dscp and Ecn.

public byte TypeOfService { get; set; }

Property Value

byte

Methods

GetPacketLength(ReadOnlySpan<byte>)

Reads an IPv4 packet's total length from its header, without parsing the rest.

public static int GetPacketLength(ReadOnlySpan<byte> buffer)

Parameters

buffer ReadOnlySpan<byte>

The packet's first bytes, at least 4.

Returns

int

The total length field: the packet's length in bytes, header included.

Exceptions

ArgumentException

The bytes are no IPv4 packet, or fewer than 4.

IndexOutOfRangeException

buffer is empty.

IsHeaderChecksumValid()

Checks the header checksum against the header.

public bool IsHeaderChecksumValid()

Returns

bool

true if the checksum is valid; otherwise, false.

UpdateHeaderChecksum()

Computes the header checksum and writes it to HeaderChecksum.

public void UpdateHeaderChecksum()