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The Internet Control Message Protocol (ICMP)
An Introduction


Prof. David Bernstein
James Madison University

Computer Science Department
bernstdh@jmu.edu

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Overview
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  • Purpose:
    • Used to communicate IP status and error messages
  • Specifications:
    • RFC 792
  • Note:
    • ICMP describes the format of the payload of "special" IP frames
Frame Format
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  • Header
    • Type (8 bits)
    • Code (8 bits)
    • Checksum (16 bits)
  • Body
    • Varies by type
Message Types
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  • Echo (a.k.a., ping) Reply
  • Destination Unreachable
  • Source Quench
  • Redirect
  • Echo (a.k.a., ping)
  • Time Exceeded
  • Parameter Problem
  • Timestamp
  • Timestamp Reply
  • Information Request
  • Information Reply
  • Address Mask Request
  • Address Mask Reply
There's Always More to Learn
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