Just in case anyone wants to know, a /30 is the smallest IP subnet on a multi-point network. It has four IP addresses: a network address used for routing, two assignable IP addresses -- one for the connected device and one for the router, and a broadcast address.
Smaller subnets are possible, in certain instances:
- /31 subnets (two IP addresses) may be possible for point-to-point network segments. (You can find examples of /31 implementations by searching the Internet, but I have never tested one.)
- /32 subnets (one IP address) are usable with loopback and alias addresses.