CIDR/IP Range Converter

Instantly Convert Between CIDR Notation and IP Ranges

Free online CIDR/IP range converter. Perform bidirectional conversion from CIDR notation (e.g., 192.168.1.0/24) to IP address ranges, or from IP address ranges to CIDR notation in real-time. Perfect tool for network administrators, security engineers, and infrastructure designers. Fully supports IPv4 and all calculations are performed in your browser.

How to Use

CIDR/IP range conversion in 3 simple steps:

Step 1: Select Conversion Direction
Choose either 'CIDR → IP Range' tab or 'IP Range → CIDR' tab. Select the former if you want to know the IP address range from CIDR notation, or the latter if you want to express an IP address range in CIDR notation.
Step 2: Enter Input Values
For CIDR → IP Range: Enter CIDR notation (e.g., 192.168.1.0/24). For IP Range → CIDR: Enter start IP address (e.g., 192.168.1.0) and end IP address (e.g., 192.168.1.255).
Step 3: Execute Conversion
Click the 'Convert' button to instantly display conversion results. CIDR → IP Range shows network address, broadcast address, usable host range, total hosts, etc. IP Range → CIDR displays a list of optimal CIDR blocks.

All conversions are performed in your browser. Entered IP addresses are not sent to the server, ensuring complete privacy protection.

CIDR/IP Range Conversion Tool

CIDR Notation

Start IP Address

End IP Address

Practical Use Cases

CIDR/IP Range Converter can be utilized in various network management scenarios:

1. Firewall Rule Configuration

When configuring firewall or access control list (ACL) settings, you often need CIDR notation to specify allowed/denied IP address ranges. For example, if you want to allow access from 192.168.1.0 to 192.168.1.255, IP Range → CIDR conversion gives you '192.168.1.0/24' CIDR notation. Conversely, to confirm what IP address range an existing CIDR rule '10.0.0.0/16' actually covers, CIDR → IP Range conversion is useful.

2. Cloud Security Group Configuration

Cloud environments like AWS, Azure, and GCP use CIDR notation in security group and network ACL configurations. When you want to allow access only from specific offices or data centers, you need to convert their IP ranges to CIDR notation. For example, convert company IP range '203.0.113.0 - 203.0.113.127' to CIDR notation '203.0.113.0/25' and set it in security group rules.

3. Network Design and Subnet Division

When designing corporate networks or data centers, you need to appropriately divide the entire IP address space among departments or services. Using CIDR → IP Range conversion, you can confirm how many hosts each CIDR block (e.g., 10.0.1.0/24, 10.0.2.0/24) can actually support. Also, deriving optimal CIDR blocks from existing IP ranges enables efficient use of address space.

4. IP Address Inventory Management

In ISP or enterprise networks, IP address inventory management is important. You can calculate the number of actually usable IP addresses from CIDR notation-managed address blocks, or consolidate multiple consecutive IP ranges into efficient CIDR blocks. For example, from 192.168.0.0/24 (256 addresses), exclude already-used 192.168.0.0/26 (64 addresses) and express remaining addresses in optimal CIDR blocks.

5. Log Analysis and Security Monitoring

When analyzing security logs or access logs, you may want to filter access from specific IP address ranges. Check if IP addresses recorded in logs are included in specific CIDR blocks, or identify IP ranges showing suspicious access patterns, convert to CIDR notation, and add to blocklists. For example, block IP range '203.0.113.128 - 203.0.113.191' identified as attack source as '203.0.113.128/26'.

What is CIDR/IP Range Conversion?

CIDR (Classless Inter-Domain Routing) notation and IP address ranges are two different methods of expressing IP address ranges on networks. Converting between them makes network design and security configuration more efficient.

How CIDR Notation Works and Its Benefits

CIDR notation expresses IP address ranges concisely in the format 'IP address/prefix length'. Example: **192.168.1.0/24**. The prefix length (/24) indicates the number of network portion bits, with remaining bits being the host portion. For /24, the first 24 bits (192.168.1) are the network portion, and the remaining 8 bits (0-255) are the host portion. **Benefits**: (1) **Conciseness** - Express 256 IP addresses in one notation, (2) **Hierarchy** - Clearly express network hierarchical structure, (3) **Standardization** - Widely adopted in routing, firewalls, cloud configurations, (4) **Efficiency** - Reduce routing table size. Unlike traditional classful addressing (Class A/B/C), CIDR enables flexible subnet division and efficient use of IP address space.

Relationship Between IP Address Ranges and CIDR

IP address ranges express consecutive IP address ranges in the format 'start IP address - end IP address'. Example: **192.168.1.0 - 192.168.1.255**. While this format is intuitive and easy to understand, it's not suitable for routing or firewall rules. **Need for CIDR Conversion**: (1) **Firewall Configuration** - Most firewalls require CIDR notation, (2) **Routing** - Routing protocols like BGP and OSPF use CIDR notation, (3) **Cloud Configuration** - Security groups in AWS, Azure, GCP use CIDR notation, (4) **Efficient Aggregation** - Express multiple IP ranges with minimum number of CIDR blocks. However, not all IP ranges can be expressed with a single CIDR block. For example, 192.168.1.10 - 192.168.1.50 is expressed as a combination of multiple smaller CIDR blocks.

Conversion Algorithms and Optimization

**CIDR → IP Range**: (1) Calculate subnet mask from prefix length (/24 → 255.255.255.0), (2) Get network address by AND operation of IP address and subnet mask, (3) Calculate broadcast address by setting all host portion bits to 1, (4) Network address + 1 = first host, broadcast address - 1 = last host. **IP Range → CIDR**: Requires more complex algorithm. (1) Calculate range size from start IP and end IP, (2) Check if start IP is aligned to power-of-2 boundary, (3) Extract maximum CIDR block (starts from start IP, ends at or before end IP), (4) Recursively process remaining range, (5) Finally generate list of multiple CIDR blocks. This tool is optimized to cover given IP ranges with minimum number of CIDR blocks, minimizing the number of firewall rules.

Frequently Asked Questions

What is a CIDR/IP Range Converter?

A CIDR/IP Range Converter is a tool that converts between CIDR notation (e.g., 192.168.1.0/24) and IP address ranges (e.g., 192.168.1.0 - 192.168.1.255). Used for network management, firewall configuration, and cloud security group setup. All conversions are executed in your browser, and entered IP addresses are not sent to the server.

What do CIDR notations /24, /16, /8 mean?

The CIDR prefix length (such as /24) indicates how many of the 32 bits in an IP address constitute the network portion. **/8** - Class A equivalent (16,777,216 addresses, e.g., 10.0.0.0/8), **/16** - Class B equivalent (65,536 addresses, e.g., 172.16.0.0/16), **/24** - Class C equivalent (256 addresses, e.g., 192.168.1.0/24), **/32** - Single host address (1 address). The smaller the prefix length, the more IP addresses it contains. Example: /24 is 256 addresses, /23 is 512 addresses, /22 is 1024 addresses.

Can all IP ranges be converted to CIDR notation?

No, not all IP ranges can be expressed with a single CIDR block. CIDR blocks contain a power-of-2 number of addresses and require the start address to be aligned to specific boundaries. For example, **192.168.1.0 - 192.168.1.255** can be expressed as a single CIDR block **192.168.1.0/24**, but **192.168.1.10 - 192.168.1.50** requires a combination of multiple smaller CIDR blocks. This tool automatically calculates the minimum number of CIDR blocks to cover the given IP range.

What's the difference between subnet mask and wildcard mask?

**Subnet mask** indicates which part of an IP address is the network portion. Network portion bits are 1, host portion bits are 0. Example: /24 subnet mask is 255.255.255.0 (11111111.11111111.11111111.00000000 in binary). **Wildcard mask** is bit-inverted subnet mask. Host portion bits are 1, network portion bits are 0. Example: /24 wildcard mask is 0.0.0.255. Wildcard masks are used in Cisco router ACL configuration and OSPF network specification.

How do you use /31 and /32 CIDR blocks?

**/32** - Represents a single host address (1 address). Example: 192.168.1.10/32 refers only to 192.168.1.10. Used when allowing/denying specific IP addresses in firewalls or setting host routes (routes to specific hosts). **/31** - Special subnet for Point-to-Point connections (2 addresses). Defined in RFC 3021, used when only two hosts are needed, such as connections between routers. Traditionally, two addresses were lost for network and broadcast addresses, but /31 omits these, efficiently using two addresses.

What's the difference between private and public IP addresses?

**Private IP addresses** are not routed on the Internet and are used only in local networks within organizations. RFC 1918-defined ranges: **10.0.0.0/8** (10.0.0.0 - 10.255.255.255), **172.16.0.0/12** (172.16.0.0 - 172.31.255.255), **192.168.0.0/16** (192.168.0.0 - 192.168.255.255). **Public IP addresses** are globally unique on the Internet, used for Internet communication. Private IP addresses access the Internet through NAT. Enterprises and home networks use private IP addresses, conserving limited public IP addresses.

How does this tool work? Is data secure?

This CIDR/IP Range Converter executes all conversions in JavaScript within your browser. Operation process: (1) User enters CIDR notation or IP range, (2) JavaScript validates input, (3) Converts IP addresses to 32-bit integers, (4) Calculates network address, broadcast address, host range using bit operations, (5) Displays results. **No data is sent to the server**. Since all calculations are completed within your browser, privacy is completely protected and it can be used in offline environments. Corporate internal IP address information can also be converted safely.

Can multiple CIDR blocks be aggregated into one?

Yes, if multiple consecutive CIDR blocks are aligned to power-of-2 boundaries, they can be aggregated into one larger CIDR block. Example: **192.168.0.0/24** and **192.168.1.0/24** can be aggregated to **192.168.0.0/23** (512 addresses). However, aggregation has conditions: (1) Address ranges are consecutive, (2) Start address is aligned to appropriate boundary, (3) Range size is power-of-2. Using this tool's IP Range → CIDR conversion feature, you can enter ranges of multiple CIDR blocks and get optimally aggregated CIDR blocks.