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IP Subnet Calculator
IP Address:
. . .
Subnet mask/bits in mask:
Subnets to display:

IP address: 10.1.1.5
IP class: A
Subnet mask: 255.255.255.0
Subnet address: 10.1.1.0
Bits in mask: 24
Number of hosts: 254
Subnet addr First host Last host Subnet mask Broadcast
10.1.1.0 10.1.1.1 10.1.1.254 255.255.255.0 10.1.1.255
10.1.2.0 10.1.2.1 10.1.2.254 255.255.255.0 10.1.2.255
10.1.3.0 10.1.3.1 10.1.3.254 255.255.255.0 10.1.3.255
10.1.4.0 10.1.4.1 10.1.4.254 255.255.255.0 10.1.4.255

This subnet calculator can help you with the following tasks:

  • Identify subnet parameters for a given IP address and subnet mask (or CIDR prefix).
  • Display subnet parameters for a number of consecutive subnets of the specified length.
CIDR stands for Classless Inter-Domain Routing. CIDR refers to a method for allocating IP addresses and routing Internet Protocol packets.

Number of hosts on a /31 subnet:
Generally, within a subnet, two host addresses - all-zeros and one all-ones are reserved as network address and broadcast, respectively. The same approach applied to a /31 subnet with only two possible addresses in the host identifier would leave no usable addresses for host assignment. RFC3021: Using 31-Bit Prefixes on IPv4 Point-to-Point Links allows assignment of the all-zeros and one all-ones IP addresses to hosts on point-to-point links.