I am working on a change in a Java EE application that would authenticate based on the user's IP address using ServletRequest.getRemoteAddr. We store IP address ranges (FROM_IP and TO_IP) in a database and the system would authenticate only if a user's IP address falls in a range.
Now, testers have pointed out that digit 0 (zero) should not be allowed in FROM_IP and TO_IP values (in any place). Note that this is an Internet facing application, and so we will get only public IP addresses.
Are testers right in suggesting that validation? Why can't we have zero in the range value such as in 167.23.0.1 - 167.23.255.255?
No, they are completely incorrect.
In fact, this is a valid IP address:
192.168.24.0As is
167.23.0.1.Separation of the IP address into dotted segments is a purely human convenience for display. It's a lot easier to remember
192.168.1.42than3232235818.What matters to computers is the separation (netmask). It's not valid to have an host address with the host section of the address set entirely to 0 or 1.
So, 192.168.24.0 as long as the netmask is such that some bits get set in the host part. See the following calculations:
In this case, the address part (right side) has 2 bits set. This is a valid host address in the 192.168.0.0/16 subnet.
In this case, the address part has 10 bits set and 6 bits unset. This is another valid host address in the same subnet.
In this case, the address part has zero bits set. This is not a valid host address in the 192.168.24.0/24 network.
Unless I'm misunderstanding, your testers are dead wrong. Valid IP addresses can certainly have a 0 in them.
In general: No, it doesn't matter if there is a 0 in the address or not.
However, there is a grain of truth in what your testers are saying. In some cases old or broken network equipment will not work correctly on addresses with 0 in the last octests. This is due to the old classfull routing rules. In Classfull routing, you can tell the netmask from the first octet of the address. If the equipment still follows classfull routing rules it is likely to handle an address like 200.100.1.0/16 incorrectly.
Let's say you need 510 IP adresses in one range and your network adress is 192.1.1.0, you would have a /23 subnet, of which one of your host IP's is a .0 IP address, your testers are wrong if the .0 address is a host address. If you have a /24 network it would be right to say it was wrong.
To provide a very simple answer: One or more zeros in an ip address are perfectly valid for host addresses as long as those addresses are not the network or broadcast address.
Network and broadcast addresses are valid ip addresses, they're just not usable by hosts.
If the network range contains more than 256 IPv4 addresses, some of them will contain one or more zeros. As IPv4 addresses are classless you can use
sipcalcto verify.