Computer Network: ICMP

주제무·2022년 11월 1일


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Network Layer


Internet Control Message

ICMP is used for communicating with hosts and router.

There are two types of usage.

  • error report
  • query message for dianosing network problems

Error report

  • discard packet
    • destination is not in routing table
    • time exceeded; TTL is equal 1
    • source quench
    • parameter issue
  • redirection


  • 8bytes is transport layer header
  • IP header following ICMP header is datagram received by router

prior IP packet

  • IP header + data(8bytes + rest)

add ICMP header

  • ICMP header + IP header + data(8bytes + rest)

and then, add IP header

  • IP header + ICMP header + IP header + data(8bytes + rest)

Query message

  • echo request and reply; Ex> ping command
  • etc..

ICMP type and code table

There are two application, ping and traceroute using ICMP packet.

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