Solicited-Node Multicast IPv6 Address, How Solicited Node Multicast IPv6 Address are generated

In Address Resolution Protocol (ARP), ARP Requests are sent to Limited Broadcast IPv4 Address. Broadcasts are inefficient way of network communication. Broadcasts consume network bandwidth and processing power of devices. There is no ARP in IPv6. Instead IPv6 uses Neighbour Discovery Protocol (NDP) Neighbour Solicitation and Advertisement messages for Link-layer address resolution.

In IPv6, Neighbour Discovery Protocol (NDP) Neighbour Solicitation messages are sent to Solicited-Node Multicast IPv6 address.

Solicited-Node IPv6 multicast addresses are derived from the unicast IPv6 address of the interface. Solicited-Node IPv6 multicast addresses have a network prefix of FF02::1:FF00:0/104 and the remaining 24 bits are taken from the unicast IPv6 address.

I will explain this with an example.

Consider a Global Unicast IPv6 Address 2001:db8:aaaa:1::1111:777f/64. The last 24 bits are the last 6 hexadecimal digits 11777F (in binaries 000100010111011101111111). The complete Solicited-Node IPv6 multicast address is the Solicited-Node prefix (FF02::1:FF00:0/104) prepended to 11777F.

The Solicited-Node IPv6 multicast address for above Global Unicast IPv6 address is FF02::1:FF11:777F

The main advantage behind using Solicited-Node Multicast IPv6 address is that only the interface which is configured with the particular Unicast IPv6 address will be listening to Solicited-Node Multicast IPv6 address. All other interfaces are not disturbed every time a Neighbour Solicitation message is sent to the Solicited-Node Multicast IPv6 address, which belongs to another interface.

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