CIDR to IP Range Calculator

How do I calculate the IP range from a CIDR?

To calculate the IP range from a CIDR notation:

1. Determine the network address (first address in the range)
2. Calculate the broadcast address (last address in the range)
3. The usable host range is all addresses between network and broadcast
4. For a CIDR like 192.168.1.0/24:
   • Network: 192.168.1.0
   • Broadcast: 192.168.1.255
   • Usable: 192.168.1.1 - 192.168.1.254

What's the difference between /32 and /31 CIDR blocks?

/32 represents a single host address (no usable hosts), while /31 is a special case used for point-to-point links that has no network or broadcast addresses (both addresses are usable).

How do I calculate the subnet mask from CIDR notation?

The subnet mask can be derived by setting the first N bits (where N is the CIDR number) to 1 and the remaining to 0. For example:

• /24 = 255.255.255.0 (24 ones followed by 8 zeros)
• /20 = 255.255.240.0 (20 ones followed by 12 zeros)

What is a wildcard mask?

A wildcard mask is the inverse of a subnet mask, used in access control lists (ACLs) and routing protocols. It identifies which bits in an IP address should be matched (0) and which can vary (1).

How many usable IPs are in a /28 network?

A /28 network has 16 total addresses (2^(32-28)), with 14 usable hosts (subtracting network and broadcast addresses).

Can I use the first and last addresses in a subnet?

Typically no - the first address is the network identifier and the last is the broadcast address. However, in /31 networks (point-to-point links), both addresses are usable.

How do I determine if two IPs are in the same subnet?

Compare the network portions of the IPs using the subnet mask. If the network addresses match, they're in the same subnet.

What's the largest CIDR block I can use?

The smallest CIDR is /0 (all IPs) and the largest is /32 (single host). Practical limits depend on your network requirements.