ICMP

• Internet Control Message Protocol
• This is out of order, but it very directly apply here.
• Pages 582 - 585
• It is built on top of ip, but it is needed by people doing ip.
  • ICMP packets are encapsulated within IP packets.
  • Delivery is not guaranteed.
• This tool is used exclusively for controlling IP networks.
• Both for IPV4 and IPV6
• RFCs 792, 1122
• All ICMP packets contain
  • An 8 bit type field, indicating the type of message.
  • A 8 bit code field, which can contain short parameters.
  • A 16 bit checksum
• Other fields depend on the type of message.
• Look at Wikipedia for a partial list of types, codes, ...
  • We have talked about echo-reply (0) and echo-request (8)
  • We have also discussed time exceeded( 11).
  • Redirect (5) is used to notify a entity that it is sending packets to the wrong next hop.
  • Destination Unreachable (3) seams reasonable too.
  • Source quench (4) becomes important here.
• Stallings gives us this picture:
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