IPv6: Can one use more than 64 bits for the network ID

Solution 1:

Some IPv6 implementations allowed netmasks to be smaller than /64, but the last I saw those died in the 1990's. The modern ones only allow /64 because of RFC and how auto-addressing works. The network part is always 64-bits. When Comcast and company get around to passing out IPv6 to customers, they'll likely be passing out a /64 when they do. When I go to my upstream and ask for an allocation I'll probably get a /48, which I'll then chop into /64's for each subnet I need.

How the addresses end up written in the network documentation is another matter though.

Solution 2:

It says typically - of course other prefix lengths would be as valid as well. See RFC 4291 section 2.3 for reference - it does not impose any limits on prefixes.

Solution 3:

It is possible, but only recommended in special situations. One example is using a /127 on point-to-point links. I have also seen /48 prefixes on a datacenter colocation LAN, where each customer is allowed to use a /64. Weird, but it happens...