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CIDR Calculator

IP Address / CIDR
Network Information
Network Address:
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Broadcast Address:
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First Usable IP:
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Last Usable IP:
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Subnet Mask:
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Wildcard Mask:
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Total Addresses:
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Usable Hosts:
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IP Class:
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Network Type:
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Binary Representation
Network: -
Mask: -

About CIDR Notation

CIDR (Classless Inter-Domain Routing) is a method for allocating IP addresses and routing that replaces the older classful network design. CIDR notation represents an IP address and its associated routing prefix with a slash (/) followed by the prefix length.

For example, 192.168.1.0/24 represents the network with:

  • Network address: 192.168.1.0
  • Subnet mask: 255.255.255.0 (24 bits set to 1)
  • 256 total addresses (192.168.1.0 - 192.168.1.255)
  • 254 usable host addresses (excluding network and broadcast)

Common CIDR Notations

CIDR Subnet Mask Wildcard Mask Total IPs Usable Hosts
/32255.255.255.2550.0.0.011
/31255.255.255.2540.0.0.122*
/30255.255.255.2520.0.0.342
/29255.255.255.2480.0.0.786
/28255.255.255.2400.0.0.151614
/27255.255.255.2240.0.0.313230
/26255.255.255.1920.0.0.636462
/25255.255.255.1280.0.0.127128126
/24255.255.255.00.0.0.255256254
/23255.255.254.00.0.1.255512510
/22255.255.252.00.0.3.2551,0241,022
/21255.255.248.00.0.7.2552,0482,046
/20255.255.240.00.0.15.2554,0964,094
/16255.255.0.00.0.255.25565,53665,534
/8255.0.0.00.255.255.25516,777,21616,777,214
* /31 networks (RFC 3021) are used for point-to-point links

Private IP Address Ranges (RFC 1918)

These address ranges are reserved for private networks and are not routable on the public Internet:

  • 10.0.0.0/8 - 10.0.0.0 to 10.255.255.255 (16,777,216 addresses)
  • 172.16.0.0/12 - 172.16.0.0 to 172.31.255.255 (1,048,576 addresses)
  • 192.168.0.0/16 - 192.168.0.0 to 192.168.255.255 (65,536 addresses)

Special-Use IPv4 Addresses

  • 0.0.0.0/8 - Current network (only valid as source address)
  • 127.0.0.0/8 - Loopback addresses (127.0.0.1 is localhost)
  • 169.254.0.0/16 - Link-local addresses (APIPA - Automatic Private IP Addressing)
  • 224.0.0.0/4 - Multicast addresses (224.0.0.0 to 239.255.255.255)
  • 240.0.0.0/4 - Reserved for future use (240.0.0.0 to 255.255.255.255)
  • 255.255.255.255/32 - Broadcast address for current network

IPv4 Address Classes (Legacy)

Before CIDR, IPv4 addresses were allocated using classful networking:

  • Class A: 0.0.0.0 to 127.255.255.255 (1.0.0.0 to 126.0.0.0 usable, /8 networks)
  • Class B: 128.0.0.0 to 191.255.255.255 (128.0.0.0 to 191.255.0.0 usable, /16 networks)
  • Class C: 192.0.0.0 to 223.255.255.255 (192.0.0.0 to 223.255.255.0 usable, /24 networks)
  • Class D: 224.0.0.0 to 239.255.255.255 (Multicast)
  • Class E: 240.0.0.0 to 255.255.255.255 (Reserved)

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