Design thinking of Solicitation node address in IPv6 Recently I study RFC 4291, and the solicitation node address is defined in that spec. I know what and the function of this solicitation node address. But just wondering why does the address design as FF02::1:FFXX:XXXX I mean why choose the 104 bits as fix prefix, and just use 24 bits of the unicast IP address as variation. I also know that "all nodes on the link" defined as : FF02::1 As far as I know the FF02 means multicast on the local link, but beyond that are there any correlation between them ? Any tips or references are appreciate. Thanks

> I mean why choose the 104 bits as fix prefix, and just use 24 bits of the unicast IP address as variation.

The RFC clearly explains this:

> IPv6 addresses that differ only in the high-order bits (e.g., due to multiple high-order prefixes associated with different aggregations) will map to the same Solicited-Node address, thereby reducing the number of multicast addresses a node must join.

IPv6 allows, and even requires, multiple addresses per interface. Every IPv6 unicast and anycast address that an interface has must have a corresponding solicited node address.