IPv4 Range to CIDR
Enter a start and end IPv4 address to get the corresponding CIDR blocks.
Try these examples:
What is CIDR?
CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing Internet Protocol packets. It replaced the older system based on classes A, B, and C networks.
Common Use Cases
Network planning: Optimize IP address allocation
Firewall rules: Simplify IP range configuration
ACL creation: Access control list management
CIDR Notation Explained
CIDR notation consists of an IP address, followed by a slash and a number indicating how many bits are in the network prefix. For example, in 192.168.100.0/24, the /24 indicates that the first 24 bits are the network portion.
The remaining bits (8 in this example) represent the host portion, allowing for 2^8 (256) addresses in this subnet.
Common CIDR Block Sizes
- /24 - 256 addresses (typical small network)
- /22 - 1,024 addresses (medium network)
- /16 - 65,536 addresses (large organization)
- /8 - 16,777,216 addresses (ISP/large region)
Advanced CIDR Concepts
Converting Range to CIDR
Converting an IP range to CIDR notation involves finding the largest possible CIDR blocks that cover the entire range without including any addresses outside the range. This process often results in multiple CIDR blocks representing a single IP range.
CIDR Block Boundaries
CIDR blocks must start at addresses that are multiples of their size. For example, a /24 block contains 256 addresses and must start at an address where the last octet is 0. Understanding these boundaries is crucial when converting ranges to CIDR notation.
Example Range Conversion:
| IP Range | CIDR Blocks | Addresses |
|---|---|---|
| 192.168.1.0 - 192.168.1.255 | 192.168.1.0/24 | 256 |
| 10.0.0.5 - 10.0.0.25 | 10.0.0.5/32, 10.0.0.6/31, 10.0.0.8/29, 10.0.0.16/29, 10.0.0.24/30 | 21 |
Frequently Asked Questions About IP Range to CIDR Conversion
Why would I need to convert an IP range to CIDR blocks?
Converting IP ranges to CIDR notation is essential for network planning, firewall configuration, routing table optimization, and security policy implementation. CIDR blocks are more efficient for representing IP ranges in networking equipment and software.
Why does a single IP range often convert to multiple CIDR blocks?
CIDR blocks must start at specific boundaries based on their size. Most arbitrary IP ranges cannot be represented by a single CIDR block without including addresses outside the range, so multiple blocks are needed to precisely cover the range.
What's the difference between a subnet mask and CIDR notation?
Subnet masks (like 255.255.255.0) and CIDR notation (/24) represent the same concept - how to divide an IP address into network and host portions. CIDR notation is more compact and has become the standard in modern networking.
How can I optimize the CIDR blocks for an IP range?
The optimal representation uses the fewest possible CIDR blocks that exactly cover the range. This is achieved by always using the largest possible block that fits within the range without exceeding it, then continuing with smaller blocks until the entire range is covered.