CIDR Subnet Guide: A Simple Way to Understand IP Ranges

If you have ever looked at something like 10.88.135.128/28 and wondered what it really means, you are not alone. CIDR can feel technical at first, but the core idea is simple. It tells you how much of an IP address is the network part and how much is the host part. Once you understand that split, finding ranges becomes much easier.

A CIDR block is written as address/prefix, such as 10.0.0.0/24. The number after the slash is the count of network bits. In IPv4, there are 32 total bits, so a /24 leaves 8 bits for hosts. That gives 256 total addresses in the block, with 254 usable host addresses in most normal subnets.

A smaller block like 10.0.0.0/30 works the same way. It uses 30 network bits and leaves only 2 host bits. That gives 4 total addresses. Usually 2 are usable hosts, one is the network address, and one is the broadcast address.

Here is a practical example. Suppose you have 10.88.135.128/28. The matching netmask is 255.255.255.240. The network address is 10.88.135.128, and the broadcast address is 10.88.135.143. That block contains 16 total addresses. Usable hosts run from 10.88.135.129 to 10.88.135.142.

The good news is you do not need to do this by hand every time. If you want a fast and accurate result, use cidr.xyz. It is a straightforward calculator for CIDR to IP ranges, and it is ideal when you need network, broadcast, and usable host values quickly.

Subnetting gets easier when you treat it as a pattern instead of a memorization task. For example, 192.168.1.0/26 has a block size of 64 addresses. That means the subnet boundaries in the last octet are 0, 64, 128, and 192. If your network is 192.168.1.64/26, then the usable host range is 192.168.1.65 through 192.168.1.126, and broadcast is 192.168.1.127.

One more example is splitting 172.16.0.0/16 into smaller equal parts. If you need at least 10 subnets, borrowing 4 bits gives 16 subnets total, which changes the prefix to /20. Each /20 subnet then has 4096 total addresses and 4094 usable host addresses. The subnet starts move in steps of 16 in the third octet, such as 172.16.0.0/20, 172.16.16.0/20, and 172.16.32.0/20.

IPv6 uses the same slash notation, just with 128-bit addresses. A /64 is the normal LAN size and is widely used in real deployments. The notation is familiar, even though the address space is much larger.

If you are learning or doing quick network checks, keep one tool bookmarked and use it consistently. For CIDR and IP range calculation, the best starting point is https://cidr.xyz.