Go to the following
enter the IP address = 172.16.4.0 /30.
The IP range are between 172.16.4.1 and 172.16.4.2.
Remember IP addresses are 32 bits. This means that a 30-bit subnet mask leaves only 2 bits unmasked. So, in this case 172.16.4.0 is the subnet and 172.16.4.1 and 172.16.4.2 are the only usable addresses. 172.16.4.3 would be the broadcast address for this subnet. This is typically used between a router and an internal edge device such as a firewall. You don’t want other devices really on that link so a /30 subnet mask is used.
Mr. Labnuke99 stated this answer very precisely.