Internet Control Message Protocol - ICMP Header (RFC 792)
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Byte Offset 0
Byte Offset 1
Byte Offset 2
Byte Offset 3
Message Type (8-bit)
Message Code (8-bit)
Checksum (16-bit)
Byte Offset 4
Byte Offset 5
Byte Offset 6
Byte Offset 7
(contents depends on type and code)
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Common Types & Codes
Type
Type Description
Code
Message Code Description
0
Echo reply
0
3
Destination Unreachable
0
Net Unreachable
1
Host Unreachable
2
Protocol Unreachable
3
Port Unreachable
4
Fragmentation Needed & Don't Fragment Flag Set
5
Source Route Failed
6
Destination Network Unknown
7
Destination Host Unknown
8
Source Route Isolated
9
Network Administratively Prohibited
10
Host Administratively Prohibited
11
Network Unreachable for TOS
12
Host Unreachable for TOS
13
Communication Administratively Prohibited
4
Source Quench
0
5
Redirect
0
Redirect Datagram for the Network
1
Redirect Datagram for the Host
2
Redirect Datagram for the TOS & Network
3
Redirect Datagram for the TOS & Host
8
Echo
0
9
Router Advertisement
0
10
Router Selection
0
11
Time Exceeded
0
Time to Live exceeded in transit
1
Fragment Reassembly Time Exceeded
12
Parameter Problem
0
Pointer indicates the error
1
Missing a Required Option
2
Bad Length
13
Timestamp Request
0
14
Timestamp Reply
0
15
Information Request
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16
Information Reply
0
17
Address Mask Request
0
18
Address Mask Reply
0
30
Traceroute
0
31
Datagram Conversion Error
0
37
Domain Name Request
0
38
Domain Name Reply
0
40
Photuris (RFC 2521)
0
(Note: Byte offset 4-5: identification #)