CIDR – Network Conversion

Posted on by tygaradmin

For future reference

** note to self ** /31 is for point to point, ie wireless isp to client

Bitmask (Bits) Dotted Decimal Hexadecimal Binary
/0 0.0.0.0 0x00000000 00000000 00000000 00000000 00000000
/1 128.0.0.0 0x80000000 10000000 00000000 00000000 00000000
/2 192.0.0.0 0xc0000000 11000000 00000000 00000000 00000000
/3 224.0.0.0 0xe0000000 11100000 00000000 00000000 00000000
/4 240.0.0.0 0xf0000000 11110000 00000000 00000000 00000000
/5 248.0.0.0 0xf8000000 11111000 00000000 00000000 00000000
/6 252.0.0.0 0xfc000000 11111100 00000000 00000000 00000000
/7 254.0.0.0 0xfe000000 11111110 00000000 00000000 00000000
/8 255.0.0.0 0xff000000 11111111 00000000 00000000 00000000
/9 255.128.0.0 0xff800000 11111111 10000000 00000000 00000000
/10 255.192.0.0 0xffc00000 11111111 11000000 00000000 00000000
/11 255.224.0.0 0xffe00000 11111111 11100000 00000000 00000000
/12 255.240.0.0 0xfff00000 11111111 11110000 00000000 00000000
/13 255.248.0.0 0xfff80000 11111111 11111000 00000000 00000000
/14 255.252.0.0 0xfffc0000 11111111 11111100 00000000 00000000
/15 255.254.0.0 0xfffe0000 11111111 11111110 00000000 00000000
/16 255.255.0.0 0xffff0000 11111111 11111111 00000000 00000000
/17 255.255.128.0 0xffff8000 11111111 11111111 10000000 00000000
/18 255.255.192.0 0xffffc000 11111111 11111111 11000000 00000000
/19 255.255.224.0 0xffffe000 11111111 11111111 11100000 00000000
/20 255.255.240.0 0xfffff000 11111111 11111111 11110000 00000000
/21 255.255.248.0 0xfffff800 11111111 11111111 11111000 00000000
/22 255.255.252.0 0xfffffc00 11111111 11111111 11111100 00000000
/23 255.255.254.0 0xfffffe00 11111111 11111111 11111110 00000000
/24 255.255.255.0 0xffffff00 11111111 11111111 11111111 00000000
/25 255.255.255.128 0xffffff80 11111111 11111111 11111111 10000000
/26 255.255.255.192 0xffffffc0 11111111 11111111 11111111 11000000
/27 255.255.255.224 0xffffffe0 11111111 11111111 11111111 11100000
/28 255.255.255.240 0xfffffff0 11111111 11111111 11111111 11110000
/29 255.255.255.248 0xfffffff8 11111111 11111111 11111111 11111000
/30 255.255.255.252 0xfffffffc 11111111 11111111 11111111 11111100
/31 255.255.255.254 0xfffffffe 11111111 11111111 11111111 11111110
/32 255.255.255.255 0xffffffff 11111111 11111111 11111111 11111111

Class address ranges:

Class A = 1.0.0.0 to 126.0.0.0
Class B = 128.0.0.0 to 191.255.0.0
Class C = 192.0.1.0 to 223.255.255.0

Reserved address ranges for private (non-routed) use:

10.0.0.0 -> 10.255.255.255
172.16.0.0 -> 172.31.255.255
192.168.0.0 -> 192.168.255.255

Other reserved addresses:

127.0.0.0 is reserved for loopback and IPC on the local host
224.0.0.0 -> 239.255.255.255 is reserved for multicast addresses

Chart notes:

Number of Subnets – “( )” Refers to the number of effective subnets, since the use of subnet numbers of all 0s or all 1s is highly frowned upon and RFC non-compliant.
Number of Hosts – Refers to the number of effective hosts, excluding the network and broadcast address.

Class A
Network Bits Subnet Mask Number of Subnets Number of Hosts
/8 255.0.0.0 0 16777214
/9 255.128.0.0 2 (0) 8388606
/10 255.192.0.0 4 (2) 4194302
/11 255.224.0.0 8 (6) 2097150
/12 255.240.0.0 16 (14) 1048574
/13 255.248.0.0 32 (30) 524286
/14 255.252.0.0 64 (62) 262142
/15 255.254.0.0 128 (126) 131070
/16 255.255.0.0 256 (254) 65534
/17 255.255.128.0 512 (510) 32766
/18 255.255.192.0 1024 (1022) 16382
/19 255.255.224.0 2048 (2046) 8190
/20 255.255.240.0 4096 (4094) 4094
/21 255.255.248.0 8192 (8190) 2046
/22 255.255.252.0 16384 (16382) 1022
/23 255.255.254.0 32768 (32766) 510
/24 255.255.255.0 65536 (65534) 254
/25 255.255.255.128 131072 (131070) 126
/26 255.255.255.192 262144 (262142) 62
/27 255.255.255.224 524288 (524286) 30
/28 255.255.255.240 1048576 (1048574) 14
/29 255.255.255.248 2097152 (2097150) 6
/30 255.255.255.252 4194304 (4194302) 2

Class B
Network Bits Subnet Mask Number of Subnets Number of Hosts
/16 255.255.0.0 0 65534
/17 255.255.128.0 2 (0) 32766
/18 255.255.192.0 4 (2) 16382
/19 255.255.224.0 8 (6) 8190
/20 255.255.240.0 16 (14) 4094
/21 255.255.248.0 32 (30) 2046
/22 255.255.252.0 64 (62) 1022
/23 255.255.254.0 128 (126) 510
/24 255.255.255.0 256 (254) 254
/25 255.255.255.128 512 (510) 126
/26 255.255.255.192 1024 (1022) 62
/27 255.255.255.224 2048 (2046) 30
/28 255.255.255.240 4096 (4094) 14
/29 255.255.255.248 8192 (8190) 6
/30 255.255.255.252 16384 (16382) 2

Class C
Network Bits Subnet Mask Number of Subnets Number of Hosts
/24 255.255.255.0 0 254
/25 255.255.255.128 2 (0) 126
/26 255.255.255.192 4 (2) 62
/27 255.255.255.224 8 (6) 30
/28 255.255.255.240 16 (14) 14
/29 255.255.255.248 32 (30) 6
/30 255.255.255.252 64 (62) 2

Class D
CIDR Block Supernet Mask Number of Class C Addresses Number of Hosts
/14 255.252.0.0 1024 262144
/15 255.254.0.0 512 131072
/16 255.255.0.0 256 65536
/17 255.255.128.0 128 32768
/18 255.255.192.0 64 16384
/19 255.255.224.0 32 8192
/20 255.255.240.0 16 4096
/21 255.255.248.0 8 2048
/22 255.255.252.0 4 1024
/23 255.255.254.0 2 512