PacketGen Structure

PacketGen uses 3 primary concepts:

• a packet is an object describing a network packet,

• a header is an object describing a network protocol,

• a field is of a basic or composed type. A composed type is a type based on one or

  more others composed types or basic types.

Packets

PacketGen is packet centric, so sessions or fragmentation are not handled. Thus, a packet may not contain all data necessary to interpret it.

A packet (PacketGen::Packet class) is merely a container for headers. It also has a body to handle data of most inner protocol.

A packet consists of:

• an array containing headers (PacketGen::Packet#headers),

• a body (PacketGen::Packet#body, which is a shortcut to last header's body).

Packet class also provides methods to interact with packets:

• parsing packets from binary string,

• reading packets from PCAP and PCAP-NG files,

• capturing packets from a network interface,

• writing packets to PCAP-NG files,

• helpers methods to:

  • calculate all length and checksum fields among headers,

  • serialize packet to binary data,

  • encapsulate a packet in another,

  • decapsulate some headers from a packet to a new packet.

Headers

Most of headers are based on PacketGen types. They contain fields. Each field is defined from a type.

Some headers may contain others headers. Such headers should have a #body field to handle inner headers.

Some protocols use length fields and/or checksum fields. To permit computation of these fields at once through PacketGen::Packet#calc, these fields should be named #length and #checksum, respectively.

Most of PacketGen header classes inherit from PacketGen::Header::Base class. This class implements minimal API needed to parse packets and add headers to packets.

Types

Basic types

Basic types are types used to construct headers or composed types. Basic types are listed in table below.

Type	Description
Types::Int8	8-bit integer
Types::Int8Enum	8-bit enumerated integer
Types::Int16, Types::Int16be	16-bit big-endian integer
Types::Int16Enum, Types::Int16beEnum	16-bit big-endian enumerated integer
Types::Int16le	16-bit little-endian integer
Types::Int16leEnum	16-bit little-endian enumerated integer
Types::Int32, Types::Int32be	32-bit big-endian integer
Types::Int32Enum, Types::Int32beEnum	32-bit big-endian enumerated integer
Types::Int32le	32-bit little-endian integer
Types::Int32leEnum	32-bit little-endian enumerated integer
Types::Int64, Types::Int64be	64-bit big-endian integer
Types::Int64le	64-bit little-endian integer
Types::String	binary string
Types::CString	null-terminated string
Types::IntString	binary string prepended with its field
Types::Array	container for types. May contain multiple values of a single type

Composed Types

Composed types are some PacketGen default types built from basic ones. These types are commonly used to define headers:

Type	Description
Types::Fields	a container to concatenate multiple fields of different types together
Types::TLV	Type-Length-Value type
Types::OUI	Organizationally Unique Identifier

Some headers also define commonly used types:

Type	Description
Header::Eth::MacAddr	Ethernet MAC address
Header::IP::Addr	IPv4 address
Header::IPv6::Addr	IPv6 address