A while ago I was having some conceptual barriers dealing with
sanity-checking a given IPv6 network specification, e.g.,
why are
2620:0:A0::/48
2620:0:A00::/43
2620:0:500::/41
valid but 2620:0:510::/41 not valid? So I coded up something
that would offer a bit of an explanation:
checknet 2620:0:510::/41
The network prefix has more bits than the prefix size:
2620:0000:0510:0000:0000:0000:0000:0000
^
This is the rightmost non-zero hex digit for a /41 prefix.
If non-zero, the digit must be an 8.
Otherwise, the tool the quite basic compared to the others
that were mentioned.