As with a lot of things IP related, 127.0.0.0
is the "network" address, so no host should claim it.
The subnet is defined as 127.0.0.0/8
or 127.0.0.0
with a netmask of 255.0.0.0
which means the network address is 127.0.0.0
and the broadcast address is 127.255.255.255
, both of which are reserved.
For any given subnet, the first address is considered the network, the last the broadcast. The remainder is the host addresses.
For smaller subnets, like /24
(255.255.255.0
) the range is proportionately smaller, and for some like a /29
smaller still. Any smaller is just silly as you end up with nothing more than a network and broadcast address, it's not a usable subnet.
Note: /32
isn't a subnet, it's only used as a way of saying "host address" for things like firewall rules.
Many IP stacks respond to any valid 127.0.0.0/8
address, not just 127.0.0.1
, but they will not respond to the network address.
In other words, the valid IP range is 127.0.0.1
through 127.255.255.254
for host addresses.
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