1 Figure 3-33: Internet Control Message Protocol (ICMP) ICMP is for Supervisory Messages at the Internet Layer ICMP and IP An ICMP message is delivered (encapsulated) in the data field of an IP packet Types and Codes (Figure 3-2) Type: General category of supervisory message Code: Subcategory of type (set to zero if there is no code)
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1 Figure 3-33: Internet Control Message Protocol (ICMP) ICMP is for Supervisory Messages at the Internet Layer ICMP and IP An ICMP message is delivered.
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Transcript
1
Figure 3-33: Internet Control Message Protocol (ICMP)
ICMP is for Supervisory Messages at the Internet Layer
ICMP and IP An ICMP message is delivered (encapsulated) in
the data field of an IP packet
Types and Codes (Figure 3-2) Type: General category of supervisory message Code: Subcategory of type (set to zero if there is
no code)
2
Figure 8.13: Internet Control Message Protocol (ICMP) for Supervisory Messages
“Host Unreachable”
Error Message
Router
“Echo”“EchoReply”
ICMP Message IP Header
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Figure 3-32: IP Packet with an ICMP Message Data Field
Bit 31
IP Header (Usually 20 Bytes)
Type (8 bits) Depends on Type and Code
Depends on Type and Code
Bit 0
Code (8 bits)
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Figure 3-32: Internet control Message Protocol (ICMP)
Network Analysis Messages Echo (Type 8, no code) asks target host if it is
operational and available Echo reply (Type 0, no code). Target host
responds to echo sender Ping program implements Echo and Echo Reply.
Like submarine pinging a target Ping is useful for network managers to diagnose
problems based on failures to reply Ping is useful for hackers to identify potential
targets: live ones reply
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Figure 3-32: Internet control Message Protocol (ICMP)
Error Advisement Messages Advise sender of error but there is no error