Internet Control Message Protocol Version 6 (ICMPv6) is the implementation of the Internet Control Message Protocol (ICMP) for Internet Protocol version 6 (IPv6). ICMPv6 is an integral part of IPv6 and performs error reporting, diagnostic functions (e.g., ping), neighbor discovery, and a framework for extensions to implement future Internet Protocol control aspects. ICMPv6 is defined in RFC 4443.^[1]

The Internet Protocol Suite
Application Layer
BGP · DHCP · DNS · FTP · GTP · HTTP · IMAP · IRC · Megaco · MGCP · NNTP · NTP · POP · RIP · RPC · RTP · RTSP · SDP · SIP · SMTP · SNMP · SOAP · SSH · Telnet · TLS/SSL · XMPP · (more)
Transport Layer
TCP · UDP · DCCP · SCTP · RSVP · ECN · (more)
Internet Layer
IP (IPv4, IPv6) · ICMP · ICMPv6 · IGMP · IPsec · (more)
Link Layer
ARP/InARP · NDP · OSPF · Tunnels (L2TP) · PPP · Media Access Control (Ethernet, DSL, ISDN, FDDI) · (more)
This box: view • talk • edit

Contents 1 Technical details 2 Packet format 3 Types of ICMPv6 messages 4 Operation 4.1 Message checksum 4.2 Message Processing 5 References 6 External links

[edit] Technical details

ICMPv6 messages may be classified into two categories: error messages and information messages. ICMPv6 messages are transported by IPv6 packets in which the IPv6 Next Header value for ICMPv6 is set to 58.

[edit] Packet format

The ICMPv6 packet consists of a header and the protocol payload. The header contains only three fields: Type (8 bits), Code (8 bits), and Checksum (16 bits). Type specifies the type of the message. Values in the range from 0 to 127 (high-order bit is 0) indicate an error message, and, when the high-order bit is 1 (128 to 255), it is an information message. The Code field value depends on the message type and provides an additional level of message granularity. The Checksum field provides a minimal level of integrity verification for the ICMP message.

ICMPv6 packet

Bit offset	0–7								8–15								16–31
0	Type								Code								Checksum
32	Message body

[edit] Types of ICMPv6 messages

Type	Meaning
ICMPv6 Error Messages
1	Destination Unreachable
2	Packet Too Big
3	Time Exceeded
4	Parameter Problem
100	Private experimentation
101	Private experimentation
127	Reserved for expansion of ICMPv6 error messages
ICMPv6 Informational Messages
128	Echo Request
129	Echo Reply
200	Private experimentation
201	Private experimentation
255	Reserved for expansion of ICMPv6 informational messages

Note that the table above is not comprehensive. The current complete list of assigned ICMPv6 types can be found at this link: IANA: ICMPv6 Parameters

[edit] Operation

[edit] Message checksum

ICMPv6 provides a minimal level of message integrity verification by the inclusion of a 16-bit checksum in its header. The checksum is calculated starting with a pseudo-header of IPv6 header fields according to the IPv6 standard,^[2] which consists of the source and destination addresses, the packet length and the next header field, the latter of which is set to the value 58. Following this pseudo header, the checksum is continued with the ICMPv6 message in which the checksum is initially set to zero. The checksum computation is performed according to Internet protocol standards using 16-bit one's complement summation, followed by complementing the checksum itself and inserting it into the checksum field.^[3]

[edit] Message Processing

When an ICMPv6 node receives a packet, it must undertake actions that depend on the type of message. The ICMPv6 protocol must limit the number of error messages sent to the same destination to avoid network overloading. For example, if a node continues to forward erroneous packets, ICMP will signal the error to the first packet and then do so periodically, with a fixed minimum period or with a fixed network maximum load. An ICMP error message must never be sent in response to another ICMP error message.

[edit] References

[edit] External links

• IANA: ICMPv6 Parameters
• RFC 2894, Router Renumbering for IPv6