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.
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.