Would 0.1.0.1/16 be a valid public ip address?

Question

I have a question regarding the validity of the IP address 0.1.0.1/16. After consulting the reserved IP list provided by IANA, I noticed that only the ranges 0.0.0.0/8 and 0.0.0.0/32 are listed as reserved. This leads me to wonder if addresses outside of this range, such as 0.1.0.1/16, can theoretically be used. Or Am I missing something?

Answer 1

the IP address 0.1.0.0/16

... it isn't an "IP address" (singular), but rather a range of addresses that fall into the subnet with a 16-bit mask. This is CIDR notation.

0.1.0.0/16 is:

  255    .   255    .     0    .     0
11111111 . 11111111 . 00000000 . 00000000 - subnet mask, i.e: /16, or 16x 1's

    0    .     1    .     ?    .     ?
00000000 . 00000001 . ???????? . ???????? - network address
                      xxxxxxxx . xxxxxxxx - host address

This leads me to wonder if addresses outside of this range, such as 0.1.0.0/16, can theoretically be used

It's not outside this range - 0.1.0.0/16 (i.e: 0.1.0.0 to 0.1.255.255) is wholly covered by 0.0.0.0/8 (i.e: 0.0.0.0 to 0.255.255.255).

0.0.0.0/8 is:

  255    .     0    .     0    .     0
11111111 . 00000000 . 00000000 . 00000000 - subnet mask, i.e: /8, or 8x 1's

    0    .     ?    .     ?    .     ?
00000000 . ???????? . ???????? . ???????? - network address
           xxxxxxxx . xxxxxxxx . xxxxxxxx - host address

The 0.0.0.0/8 range is listed in the IANA IPv4 Special-Purpose Address Registry, you can see that all of the addresses in this range may be a "Source", but may not be a "Destination", are not "Forwardable", and are not "Globally Reachable" - along with being "Reserved-by-Protocol".

As indicated by the registry, RFC791 Section 3.2 (and other RFCs) is a good place to start if you'd like to read into what's going on here.

A value of zero in the network field means this network. This is only used in certain ICMP messages. The extended addressing mode is undefined. Both of these features are reserved for future use.

Fundamentally, no - you can't use anything starting with 0.*