/23 Subnet

A /23 has 512 addresses, 510 of them usable by hosts. Its netmask is 255.255.254.0. Enter any address below to see its /23 network.

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Examples:

IPv4 network

510 usable hosts · 192.168.0.1 to 192.168.1.254

Private (RFC 1918)

Details

Netmask
Wildcard Mask
Broadcast
First Usable
Last Usable
Usable Hosts
Total Addresses
Netmask in Binary
Address Entered

Split Into Subnets

192.168.0.0/24192.168.0.0 – 192.168.0.255
192.168.1.0/24192.168.1.0 – 192.168.1.255

Subnet Calculator

/23 at a glance

CIDR Prefix/23
Netmask255.255.254.0
Wildcard Mask0.0.1.255
Netmask (Hex)0xFFFFFE00
Total Addresses512
Usable Hosts510
Host Bits9
Contains /24s2
Binary Mask11111111.11111111.11111110.00000000

A /23 fixes the first 23 bits of the address as the network and leaves 9 bits for hosts, so it holds 2^9 = 512 addresses. The first is the network address and the last is the broadcast address, leaving 510 for hosts.

Two /24s. Often announced as two separate /24s so either half can be moved or filtered on its own.

A /23 can be announced in BGP on its own: /24 is the longest prefix most networks accept.

Other IPv4 Prefixes

/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32

IPv6 Prefixes

IPv6 /32IPv6 /36IPv6 /40IPv6 /44IPv6 /48IPv6 /52IPv6 /56IPv6 /60IPv6 /64IPv6 /112IPv6 /126IPv6 /127IPv6 /128

Questions

How many usable IP addresses are in a /23?
510. A /23 has 512 addresses; the network and broadcast addresses are not usable by hosts.
What is the subnet mask for /23?
255.255.254.0. The wildcard (inverse) mask, used in Cisco ACLs, is 0.0.1.255.
How many /24 networks are in a /23?
2. Each step from /23 to /24 doubles the number of networks.
Is 255.255.254.0 the same as /23?
Yes. 255.255.254.0 written in binary is 23 ones followed by 9 zeros, which is what /23 means.

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