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CIDR/Netmask Lookup Tool

The CIDR/Netmask tool provides information about a CIDR range including the IP addresses and host addresses contained in it.

Enter an IPv4 or IPv6 address with optional CIDR notation, or just CIDR notation:

About this Tool

This tool provides the following IP information:

  • IPv4 and IPv6 subnet netmask (including binary and decimal expressions)
  • Number of networks and hosts available in each relevant CIDR range
  • IP Classes (e.g., IPv4 A=/8, B=/16, C=/24, etc.)
  • Netmask IP range and binary ip address

What is CIDR? Classless Inter-Domain Routing (CIDR) is an expansion of the IP addressing system that allows for a more efficient and appropriate allocation of addresses. CIDR changed fixed fields into variable-length fields, allowing addresses to be assigned with more granularity. The CIDR IP address includes a number that tells how the address is split between networks and hosts. For example, in the CIDR address the /20 indicates that the first 20 bits are used for network ID and the remaining 12 (there are 32 bits in the IP address) are used for host ID.