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Appendixes Appendix A: ICMP Types and Codes
The Internet Control Message Protocol (ICMP) has many messages that are identified by
a “type” field; many of these ICMP types have a "code" field. Here we list the types with their
assigned code fields.
Type Name Code Description Reference
0 Echo Reply 0 No Code RFC792
3 Destination Unreachable 0 Net Unreachable RFC792
1 Host Unreachable RFC792
2 Protocol Unreachable RFC792
3 Port Unreachable RFC792
4 Fragmentation Needed and
Don't Fragment was Set
RFC792
5 Source Route Failed RFC792
6 Destination Network Unknown RFC792
7 Destination Host Unknown RFC792
8 Source Host Isolated RFC792
9 Communication with
Destination Network is
Administratively Prohibited
RFC792
10 Communication with
Destination Host is
Administratively Prohibited
RFC792
11 Destination Network
Unreachable for Type of
Service
RFC792
12 Destination Host Unreachable
for Type of Service
RFC792
13 Communication
Administratively Prohibited
RFC1812
14 Host Precedence Violation RFC1812
15 Precedence cutoff in effect RFC1812
4 Source Quench 0 No Code RFC792