ICMPv6 NS and RA Messages

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ICMPv4 and ICMPv6 are very similar, most of the informational and error messages. The ICMPv6 has included some new and improved features and functions that are not available in ICMPv4. The ICMPv6 messages encapsulate in IPv6. It has four new protocols as part of the Neighbor Discovery Protocol. Messaging between an IPv6-enabled router and an IPv6-enabled device are the following:

ICMPv6

Router Solicitation (RS) message

We can configure a host computer to get addressing information automatically using SLAAC. The host will send an RS message to the router at system start-up. The RS message was sent as an IPv6 all-routers multicast message to address FF02::2.

Router Advertisement (RA) message

The router sends RA messages periodically to provide addressing information using SLAAC, such as the prefix, prefix length, DNS address, and domain name. RA messages also provide IPv6 prefixes for automatic address configuration and Information such as MTU, hop limit reachable time, and retransmission time for neighbour solicitations.

ICMPv6 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) message

ICMPv6 neighbour solicitation (NS) and advertisement messages permit a node to resolve the MAC address of another node on the same network. This function is just like the Address Resolution Protocol (ARP) function in IPv4. It is also used for Duplicate Address Detection (DAD).

Address Resolution

When the device knows the destination IPv6 unicast address on the same link but does not know the destination device’s MAC address, the Address Resolution is used to know its MAC address, similarly to an ARP Request for IPv4. To resolve the destination’s MAC address, the device will send an NS message to the solicited-node address. The message will contain the destination IPv6 unicast address. The destination device will respond with an NA message containing its Ethernet MAC address.

Duplicate Address Detection

IPv4 nodes use gratuitous ARP to detect a duplicate unicast IPv4 address on the local link. Similarly, IPv6 nodes use Neighbor Solicitation messages (NS message) to identify the uniqueness of an address on the local link in a process known as Duplicate Address Detection (DAD). The device will send an NS message with its IPv6 address as the targeted IPv6 address. If another device on the network has this address, it will respond with an NA message. This NA message will notify the sending device that the address is in use. If a corresponding NA message is not returned within a certain period, the unicast address is unique and acceptable.