CIDR / Subnet Reference

Quick reference for CIDR notation, IPv4/IPv6 subnet sizes, private ranges, special addresses, subnet examples, and wildcard masks with host counts

Related Categories:Network

73 entries

/0

Entire address space

0.0.0.0 / 4,294,967,296 hosts

/1

Half of address space

128.0.0.0 / 2,147,483,648 hosts

/4

1/16 of address space

240.0.0.0 / 268,435,456 hosts

/8

Class A equivalent

255.0.0.0 / 16,777,216 hosts

/9

Half of /8 size

255.128.0.0 / 8,388,608 hosts

/10

Half of /9 size

255.192.0.0 / 4,194,304 hosts

/12

Large private network

255.240.0.0 / 1,048,576 hosts

/16

Class B equivalent

255.255.0.0 / 65,536 hosts

/17

Half of /16 size

255.255.128.0 / 32,768 hosts

/18

Half of /17 size

255.255.192.0 / 16,384 hosts

/19

Half of /18 size

255.255.224.0 / 8,192 hosts

/20

Medium network

255.255.240.0 / 4,096 hosts

/21

Half of /20 size

255.255.248.0 / 2,048 hosts

/22

Half of /21 size

255.255.252.0 / 1,024 hosts

/23

Half of /22 size

255.255.254.0 / 512 hosts

/24

Class C equivalent (most common)

255.255.255.0 / 256 hosts

/25

Half of /24 size

255.255.255.128 / 128 hosts

/26

Small subnet

255.255.255.192 / 64 hosts

/27

Small network

255.255.255.224 / 32 hosts

/28

Very small subnet

255.255.255.240 / 16 hosts

/29

Point-to-point plus

255.255.255.248 / 8 hosts

/30

Point-to-point link

255.255.255.252 / 4 hosts (2 usable)

/31

Point-to-point only (RFC 3021)

255.255.255.254 / 2 hosts

/32

Single host

255.255.255.255 / 1 host

10.0.0.0/8

Class A private address (RFC 1918)

10.0.0.0 - 10.255.255.255

172.16.0.0/12

Class B private address (RFC 1918)

172.16.0.0 - 172.31.255.255

192.168.0.0/16

Class C private address (RFC 1918)

192.168.0.0 - 192.168.255.255

127.0.0.0/8

Loopback address

127.0.0.1 (localhost)

169.254.0.0/16

Link-local address (APIPA)

169.254.0.0 - 169.254.255.255

0.0.0.0/0

Default route (all addresses)

0.0.0.0 - 255.255.255.255

255.255.255.255/32

Limited broadcast

255.255.255.255

100.64.0.0/10

CGNAT address (RFC 6598)

100.64.0.0 - 100.127.255.255

192.0.2.0/24

Documentation address (TEST-NET-1)

192.0.2.0 - 192.0.2.255

198.51.100.0/24

Documentation address (TEST-NET-2)

198.51.100.0 - 198.51.100.255

203.0.113.0/24

Documentation address (TEST-NET-3)

203.0.113.0 - 203.0.113.255

224.0.0.0/4

Multicast address

224.0.0.0 - 239.255.255.255

/128

Single host

1 address

/127

Point-to-point link (RFC 6164)

2 addresses

/126

Point-to-point (legacy)

4 addresses

/64

Standard subnet (most common)

18,446,744,073,709,551,616 addresses

/56

End site allocation (small)

256 /64 subnets

/48

End site allocation (standard)

65,536 /64 subnets

/32

ISP allocation (minimum recommended)

65,536 /48 subnets

/16

Large ISP allocation

65,536 /32 subnets

::1/128

Loopback address

::1 (localhost)

::/0

Default route

All IPv6 addresses

fe80::/10

Link-local address

fe80:: - febf::ffff:...

fc00::/7

Unique local address (ULA)

fc00:: - fdff::ffff:...

2000::/3

Global unicast address

2000:: - 3fff::ffff:...

ff00::/8

Multicast address

ff00:: - ffff::ffff:...

::ffff:0:0/96

IPv4-mapped address

::ffff:192.0.2.1

64:ff9b::/96

NAT64 prefix

64:ff9b::192.0.2.1

2001:db8::/32

Documentation address

2001:db8:: - 2001:db8:ffff:...

192.168.1.0/24 を /25 に分割

Split 256 addresses into 2 subnets of 128 hosts

192.168.1.0/25 + 192.168.1.128/25

192.168.1.0/24 を /26 に分割

Split 256 addresses into 4 subnets of 64 hosts

192.168.1.0/26, .64/26, .128/26, .192/26

10.0.0.0/16 を /24 に分割

Split 65,536 addresses into 256 /24 subnets

10.0.0.0/24 - 10.0.255.0/24

/24 のネットワークアドレス

Network address is the first address in /24

192.168.1.0 (使用不可)

/24 のブロードキャストアドレス

Broadcast address is the last address in /24

192.168.1.255 (使用不可)

/24 の使用可能ホスト数

256 - 2 = 254 usable hosts

192.168.1.1 - 192.168.1.254

/30 の使用可能ホスト数

4 - 2 = 2 usable hosts

192.168.1.1 - 192.168.1.2

サブネット数の計算

Number of subnets = 2^(new prefix - old prefix)

/24 to /26 = 2^(26-24) = 4 subnets

0.0.0.0 (ワイルドカード)

Wildcard mask for /32 (exact match)

ACL: host 192.168.1.1

0.0.0.3

Wildcard mask for /30

4 addresses matched

0.0.0.7

Wildcard mask for /29

8 addresses matched

0.0.0.15

Wildcard mask for /28

16 addresses matched

0.0.0.31

Wildcard mask for /27

32 addresses matched

0.0.0.63

Wildcard mask for /26

64 addresses matched

0.0.0.127

Wildcard mask for /25

128 addresses matched

0.0.0.255

Wildcard mask for /24

256 addresses matched

0.0.255.255

Wildcard mask for /16

65,536 addresses matched

0.255.255.255

Wildcard mask for /8

16,777,216 addresses matched

255.255.255.255

Match all addresses (any)

ACL: any

ワイルドカード計算式

Wildcard = 255.255.255.255 - Subnet mask

255.255.255.255 - 255.255.255.0 = 0.0.0.255