Class: PacketGen::Header::GRE

Inherits:

Base

• Object
• BinStruct::Struct
• Base
• PacketGen::Header::GRE

Defined in:

lib/packetgen/header/gre.rb

Overview

Generic Routing Encapsulation (RFC 2784 and 2890)

                     1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| |K|S| Reserved0       | Ver |         Protocol Type         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Checksum (optional)      |       Reserved1 (Optional)    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Key (optional)                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 Sequence Number (Optional)                    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A GRE header is composed of:

• A first 16-bit attribute containing given flags:

  • #c indicates if #checksum and #reserved1 attributes are present.

  • #k indicates if #key attribute is present.

  • #s indicatesid #sequence_number attribute is present.

  • #ver 3-bit version number.

• #protocol_type (BinStruct::Int16).

• optional #checksum and #reserved1 attribute (both BinStruct::Int16).

• optional #key attribute (BinStruct::Int32).

• optional #sequence_number attribute (BinStruct::Int32).

• and a #body (+BinStruct::String or PacketGen::Headerable).

Current implementation supports tunneling IP and IPv6 packets in GRE.

Author:

• Sylvain Daubert

• LemonTree55

Since:

• 2.1.0

Constant Summary

IP_PROTOCOL =

IP protocol number for GRE

Since:

• 2.1.0

47

Instance Attribute Summary

• #body ⇒ BinStruct::String, Headerable
• #c ⇒ Boolean

  Say if #checksum and #reserved1 attributes are present.

• #checksum ⇒ Integer

  IP checksum over all 16-bit words in GRE header and its body.

• #k ⇒ Boolean

  Say if #key attribute is present.

• #key ⇒ Integer

  32-bit integer used to identify an individual traffic flow within a tunnel.

• #protocol_type ⇒ Integer
• #reserved0 ⇒ Integer
• #reserved1 ⇒ Integer

  Reserved field, present only if #c is set.

• #s ⇒ Boolean

  Say if #sequence_number attribute is present.

• #sequence_number ⇒ Integer (also: #seqnum)

  32-bit integer.

• #ver ⇒ Integer

  3-bit GRE protocol version.

Instance Method Summary

• #calc_checksum ⇒ Integer

  Compute checksum and set checksum attribute.

• #initialize(options = {}) ⇒ GRE constructor

  A new instance of GRE.

Methods inherited from Base

bind, calculate_and_set_length, #header_id, inherited, #ip_header, #ll_header

Methods included from PacketGen::Headerable

#added_to_packet, included, #method_name, #packet, #packet=, #parse?, #protocol_name, #read, #to_s

Constructor Details

#initialize(options = {}) ⇒ GRE

Returns a new instance of GRE.

Since:

• 2.1.0

# File 'lib/packetgen/header/gre.rb', line 87

def initialize(options={})
  opts = { r: false, reserved0: 0, version: 0 }.merge(options)
  super(opts)
end

Instance Attribute Details

#body ⇒ BinStruct::String, Headerable

Returns:

• (BinStruct::String, Headerable)

# File 'lib/packetgen/header/gre.rb', line 82

define_attr :body, BinStruct::String

#c ⇒ Boolean

Say if #checksum and #reserved1 attributes are present

Returns:

• (Boolean)

# File 'lib/packetgen/header/gre.rb', line 58

define_bit_attr :u16, c: 1, r: 1, k: 1, s: 1, reserved0: 9, ver: 3

#checksum ⇒ Integer

IP checksum over all 16-bit words in GRE header and its body. Present only if #c is set.

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 66

define_attr :checksum, BinStruct::Int16, default: 0, optional: lambda(&:c?)

#k ⇒ Boolean

Say if #key attribute is present

Returns:

• (Boolean)

# File 'lib/packetgen/header/gre.rb', line 58

define_bit_attr :u16, c: 1, r: 1, k: 1, s: 1, reserved0: 9, ver: 3

#key ⇒ Integer

32-bit integer used to identify an individual traffic flow within a tunnel. Present only if #k is set.

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 75

define_attr :key, BinStruct::Int32, optional: lambda(&:k?)

#protocol_type ⇒ Integer

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 62

define_attr :protocol_type, BinStruct::Int16

#reserved0 ⇒ Integer

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 58

define_bit_attr :u16, c: 1, r: 1, k: 1, s: 1, reserved0: 9, ver: 3

#reserved1 ⇒ Integer

Reserved field, present only if #c is set.

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 70

define_attr :reserved1, BinStruct::Int16, default: 0, optional: lambda(&:c?)

#s ⇒ Boolean

Say if #sequence_number attribute is present

Returns:

• (Boolean)

# File 'lib/packetgen/header/gre.rb', line 58

define_bit_attr :u16, c: 1, r: 1, k: 1, s: 1, reserved0: 9, ver: 3

#sequence_number ⇒ Integer Also known as: seqnum

32-bit integer. Present only if #s is set.

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 79

define_attr :sequence_number, BinStruct::Int32, optional: lambda(&:s?)

#ver ⇒ Integer

3-bit GRE protocol version.

Returns:

• (Integer)

# File 'lib/packetgen/header/gre.rb', line 58

define_bit_attr :u16, c: 1, r: 1, k: 1, s: 1, reserved0: 9, ver: 3

Instance Method Details

#calc_checksum ⇒ Integer

Compute checksum and set checksum attribute.

Returns:

• (Integer)

Since:

• 2.1.0

# File 'lib/packetgen/header/gre.rb', line 94

def calc_checksum
  sum = IP.sum16(self)
  self.checksum = IP.reduce_checksum(sum)
end