Appendix H. ICMP Type and Code Numbers

Appendix H. ICMP Type and Code Numbers

The Internet Control Message Protocol (ICMP) is used to transport error or control messages between routers and other devices. An ICMP message is encapsulated as the payload in an IP packet. Figure H-1 shows the ICMP message format. Notice that in the case of an error condition, the first 8 bytes (64 bits) of the original datagram causing the error are included in the ICMP message. This provides the protocol and port numbers of the original message to be seen, making troubleshooting easier.

Figure H-1. ICMP Message Format

ICMP type codes are registered with the Internet Assigned Numbers Authority (IANA). The information presented here is reproduced with permission from the IANA. For the most current ICMP type code number assignment information, refer to http://www.iana.org/numbers.htm under the "ICMP Type" link.

Table H-1 shows the assigned ICMP type numbers, ICMP codes (where applicable ), a brief description, and a reference to an RFC.

Table H-1. Assigned ICMP Type Numbers, Codes, Descriptions and Associated RFCs

Type	Code	Name	Reference
		Echo Reply	[RFC 792]
1		Unassigned
2		Unassigned
3		Destination Unreachable	[RFC 792]
		Net Unreachable
	1	Host Unreachable
	2	Protocol Unreachable
	3	Port Unreachable
	4	Fragmentation Needed and Don't Fragment was Set
	5	Source Route Failed
	6	Destination Network Unknown
	7	Destination Host Unknown
	8	Source Host Isolated
	9	Destination Network is administratively prohibited
	10	Destination Host is administratively prohibited
	11	Destination Network Unreachable for Type of Service
	12	Destination Host Unreachable for Type of Service
	13	Communication Administratively Prohibited	[RFC 1812]
	14	Host Precedence Violation	[RFC 1812]
	15	Precedence cutoff in effect	[RFC 1812]
4		Source Quench	[RFC 792]
5		Redirect	[RFC 792]
		Redirect Datagram for the Network (or subnet)
	1	Redirect Datagram for the Host
	2	Redirect Datagram for the Type of Service and Network
	3	Redirect Datagram for the Type of Service and Host
6		Alternate Host Address
		Alternate Address for Host
7		Unassigned
8		Echo	[RFC 792]
9		Router Advertisement	[RFC 1256]
10		Router Solicitation	[RFC 1256]
11		Time Exceeded	[RFC 792]
		Time to Live exceeded in Transit
	1	Fragment Reassembly Time Exceeded
12		Parameter Problem	[RFC 792]
		Pointer indicates the error
	1	Missing a Required Option	[RFC 1108]
	2	Bad Length
13		Timestamp	[RFC 792]
14		Timestamp Reply	[RFC 792]
15		Information Request	[RFC 792]
16		Information Reply	[RFC 792]
17		Address Mask Request	[RFC 950]
18		Address Mask Reply	[RFC 950]
19		Reserved (for Security)
20 “29		Reserved (for Robustness Experiment)
30		Traceroute	[RFC 1393]
31		Datagram Conversion Error	[RFC 1475]
32		Mobile Host Redirect
33		IPv6 Where-Are-You
34		IPv6 I-Am-Here
35		Mobile Registration Request
36		Mobile Registration Reply
37		Domain Name Request
38		Domain Name Reply
39		SKIP
40		Photuris
		Reserved
	1	Unknown security parameters index
	2	Valid security parameters, but authentication failed
	3	Valid security parameters, but decryption failed
41 “255		Reserved