Hello ADP,
2001:DB8:100::/40 is short for 2001:0db8:0100:0000:0000:0000:0000:0000/40. For this network address, the valid ranges are:
2001:0db8:0100:0000:0000:0000:0000:0000
up to
2001:0db8:01ff:ffff:ffff:ffff:ffff:ffff
2001:0DB8:01::/40 is short for 2001:0db8:0001:0000:0000:0000:0000:0000/40. (be aware of the leading zeroes) This is an address in the following range:
2001:0db8:0000:0000:0000:0000:0000:0000
up to
2001:0db8:00ff:ffff:ffff:ffff:ffff:ffff
See how this works? By specifying 2001:0DB8:01::/40, you get 2001:0DB8:0001::/40. An address of the 2001:0DB8:00::/40 network.
Hope this helps If not let me know.
Rene