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ICMP

A ICMP header consists of:

                     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
+---------------+---------------+-------------------------------+
|     Type      |      Code     |           Checksum            |
+---------------+---------------+-------------------------------+

  • 8-bit type (ICMP#type),

  • 8-bit code (ICMP#code),

  • 16-bit checksum (ICMP#checksum),

  • and a body (ICMP#body).

A ICMP header may be built this way:

pg> PacketGen::Header::ICMP.new(type: 8, code: 0, body: 'PING!')
=> ---- PacketGen::Header::ICMP -----------------------------------------
              Int8         type: 8          (0x08)
              Int8         code: 0          (0x00)
             Int16     checksum: 0          (0x0000)

A ICMP packet may be created this way:

pkt = PacketGen.gen('IP', src: '127.0.0.1', dst: '127.0.0.1').
                add('ICMP', type: 8, code: 0, body: 'PING!')
pkt.is?('IP')         # => true
pkt.is?('ICMP')       # => true
pkt.icmp              # => PacketGen::Header::ICMP
pkt.icmp.type         # => Integer
pkt.icmp.code         # => Integer
pkt.icmp.body         # => "PING!"
pkt.body              # => "PING!"

pkt.udp.type = 0 # This is now a pong!

As usual, checksum field may be computed by Header::ICMP#calc_sum. All checksum and length fields from a packet may by computed at once using pkt.calc:

See also http://rubydoc.info/gems/packetgen/PacketGen/Header/ICMParrow-up-right.

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