Re:There’s more than one way to write an IP address
by p_l on Tuesday July 09, 2019 @08:19PM
(#20398111)
0.0.0.0 is a valid address. You also have a route for 0.0.0.0/0, usually called "default" :)
Just not valid for a host, as it is a network address where "network" is specified as the whole internet. It's how you create services listening to connections from any address - technically you can setup a listening socket waiting for connections only from specific network, but I haven't tested it.
It's also why minimal compliant IPv4 network has 4 IP addresses: the network address, host 1, host 2, broadcast.
There's an unratified RFC for allowing only host 1 and host 2, but I believe it works only on some combinations of gear/software.
Then of course you get systems accepting broken setups, like 192.168.0.0 host address with /24 or /16 netmask.
However, 192.168.1.0/23 is a valid address a host can have.
Just not valid for a host, as it is a network address where "network" is specified as the whole internet. It's how you create services listening to connections from any address - technically you can setup a listening socket waiting for connections only from specific network, but I haven't tested it.
It's also why minimal compliant IPv4 network has 4 IP addresses: the network address, host 1, host 2, broadcast. There's an unratified RFC for allowing only host 1 and host 2, but I believe it works only on some combinations of gear/software.
Then of course you get systems accepting broken setups, like 192.168.0.0 host address with /24 or /16 netmask.
However, 192.168.1.0/23 is a valid address a host can have.