Understanding ICMPv6 Messages

Internet Control Message Protocol (ICMP) for IPv4 (ICMPv4) is used in IPv4 networks to allow nodes to send and respond to error messages and informational messages. For example, when a source node uses the ping command to send ICMP Echo Request messages (ICMP type 8 messages) to a destination node, the destination node can respond with ICMP Echo messages (ICMP type 0 messages) indicating its presence on the network.

On IPv6 networks, ICMP for IPv6 (ICMPv6) fulfills the same functions as ICMPv4 on IPv4 networks-namely, to provide a mechanism for exchanging error messages and informational messages. ICMPv6 also provides informational messages for the following:

• Neighbor Discovery (ND) The process by which hosts and routers discover each other on the network so that they can communicate at the data-link layer. (ND serves the same purpose as Address Resolution Protocol [ARP] does in IPv4 networks.)
• Multicast Listener Discovery (MLD) The process by which membership in multicast groups is determined and maintained.

Note For more information about ND, see the next section titled "Understanding Neighbor Discovery." For more information about ICMPv6 message types and header formats and about MLD, see the white paper, "Introduction to IP Version 6," at http://www.microsoft.com/downloads/details.aspx?FamilyID=CBC0B8A3-B6A4-4952-BBE6-D976624C257C&displaylang=en.