CIDR Range Visualiser

Understanding CIDR notation

CIDR (Classless Inter-Domain Routing) notation represents an IP address range using a base address and a prefix length separated by a slash. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for host addresses — giving 256 total addresses (254 usable).

The prefix length determines how large the network is. A smaller prefix means a larger network: /8 contains ~16.7 million addresses, while /30 contains just 4 (2 usable). CIDR replaced the old classful system, allowing networks to be divided at any bit boundary instead of only at /8, /16, or /24.

Why visualise CIDR ranges?

When planning network architecture, it's critical to ensure address ranges don't overlap. Overlapping ranges cause routing conflicts, split-brain DNS issues, and unpredictable packet delivery. This is especially common when:

• Merging networks from different offices or acquired companies
• Setting up VPN tunnels between sites with independently assigned ranges
• Planning VPC/VNET peering in cloud environments (AWS, Azure, GCP)
• Allocating subnets from a parent CIDR block

Overlap vs supernet

Two ranges overlap when they share some addresses but neither fully contains the other — e.g. 10.0.0.0/16 and 10.0.128.0/17 partially overlap. A supernet relationship exists when one range is entirely contained within another — e.g. 10.0.0.0/8 fully contains 10.10.0.0/16. Both situations need attention: overlaps cause conflicts, while supernets may indicate unintended redundancy in routing tables.

Common CIDR block sizes

/8 (16,777,216 addresses)

Class A equivalent. Used for major allocations like 10.0.0.0/8 private space.

/16 (65,536 addresses)

Class B equivalent. Common for campus or large site networks.

/24 (256 addresses)

Class C equivalent. The most common subnet size for LANs and VLANs.

/28 (16 addresses)

Small subnet. Common for DMZs, management networks, and point-to-point links.

/30 (4 addresses)

Point-to-point links between routers. Only 2 usable host addresses.

/32 (1 address)

Host route. Represents a single IP address, used in routing tables and ACLs.

Subnetting best practices

When dividing a network into subnets, always plan for growth. A common approach is to allocate from the top of a range downward for infrastructure (management VLANs, server subnets) and from the bottom upward for user subnets. Document every allocation in an IPAM system and use this visualiser to verify ranges before committing changes to production routing configurations.