IPv6 & neighbor discovery messages

The next-generation Internet Protocol (IPv6) standard, IPv6, is designed to ultimately replace IPv4, which is still used by many Internet services today. 

A numerical IP address is required for every computer, smartphone, and other device connected to the Internet in order to interact with other devices. The IPv4 protocol, the first IP address scheme, is out of addresses. The main distinction between IPv6 and IPv4 is the expansion of the IP address from 32 bits to 128 bits in IPv6.

IPV6 neighbor discovery messages
Neighbor Discovery Messages re performed with the below messages

Router Solicitation : To find IPv6 routers on the connection, IPv6 hosts issue Router Solicitation messages. Instead of waiting for a recurring Router Advertisement message, hosts send multicast Router Solicitation messages to IPv6 routers to force them to react right away.

Router Advertisement: Router Advertisement messages are sent by IPv6 routers either on a regular basis or in response to the receipt of Router Solicitation messages. The details needed for hosts to decide on link prefixes, link MTU, whether or not to employ address autoconfiguration, and the time period during which addresses generated by address autoconfiguration are both valid and preferable are contained in router advertisement messages.

Neighbor Solicitation: To learn the link-layer addresses of IPv6 nodes that are on a given link, IPv6 hosts send neighbor solicitation messages. The link-layer address of the sender is included in neighbor solicitation messages. Hosts send Neighbor Solicitation messages to unicast addresses to confirm a neighboring node may be reached as well as to multicast addresses to resolve addresses.

Neighbor Advertisement: In response to receiving Neighbor Solicitation messages, IPv6 nodes send Neighbor Advertisement messages. In order to alert nearby nodes of changes in link-layer addresses, nodes also transmit unsolicited Neighbor Advertisements. Neighbor Advertisement messages provide data that nodes need to identify the message's kind, the sender's link-layer address, and the sender's function within the network.

Redirect: Redirect messages are sent by IPv6 routers to alert originating hosts of a more suitable first-hop address for a given destination. Redirect messages are exclusively sent by routers for unicast traffic and only to originating hosts. Redirect messages are processed only by hosts.

All Neighbor Discovery messages are sent with a hop limit of 255 to guarantee that they were all transmitted by a node on the local network. The Hop Limit field in the IPv6 header is examined when a Neighbor Discovery message is obtained.

The message is quietly rejected if the field's value is not set to 255. Network attacks based on Neighbor Discovery and launched from off-link nodes can be prevented by ensuring that the hop limit of the Neighbor Discovery packet is 255. A router could not have forwarded a message from an off-link node if it had a hop limit of 255.