Glossary - Network mask

The "network mask" (or "netmask" or simply "mask") is a value that defines the subnet of an IPv4 address.  It accounts for all 32-bits of the IP address at the bit-level by splitting it into "networks" and "hosts" portions.

Usually the mask is expressed with the IP address either in CIDR notation (where the number of bits in the mask that identifies the "networks" portion is preceeded by a slash), or separately in the same format as the IPv4 address itself (often referred to as "dotted-decimal").

Reference chart

CIDR/bits	Dotted-decimal	Hexadecimal	Binary	Hosts
/0	0.0.0.0	00 00 00 00	00000000 00000000 00000000 00000000	4,294,967,296
/1	128.0.0.0	80 00 00 00	10000000 00000000 00000000 00000000	2,147,483,648
/2	192.0.0.0	c0 00 00 00	11000000 00000000 00000000 00000000	1,073,741,824
/3	224.0.0.0	e0 00 00 00	11100000 00000000 00000000 00000000	536,870,912
/4	240.0.0.0	f0 00 00 00	11110000 00000000 00000000 00000000	268,435,456
/5	248.0.0.0	f8 00 00 00	11111000 00000000 00000000 00000000	134,217,728
/6	252.0.0.0	fc 00 00 00	11111100 00000000 00000000 00000000	67,108,864
/7	254.0.0.0	fe 00 00 00	11111110 00000000 00000000 00000000	33,554,432
/8	255.0.0.0	ff 00 00 00	11111111 00000000 00000000 00000000	16,777,216
CIDR/bits	Dotted-decimal	Hexadecimal	Binary	Hosts
/9	255.128.0.0	ff 80 00 00	11111111 10000000 00000000 00000000	8,388,608
/10	255.192.0.0	ff c0 00 00	11111111 11000000 00000000 00000000	4,194,304
/11	255.224.0.0	ff e0 00 00	11111111 11100000 00000000 00000000	2,097,152
/12	255.240.0.0	ff f0 00 00	11111111 11110000 00000000 00000000	1,048,576
/13	255.248.0.0	ff f8 00 00	11111111 11111000 00000000 00000000	524,288
/14	255.252.0.0	ff fc 00 00	11111111 11111100 00000000 00000000	262,144
/15	255.254.0.0	ff fe 00 00	11111111 11111110 00000000 00000000	131,072
/16	255.255.0.0	ff ff 00 00	11111111 11111111 00000000 00000000	65,536
CIDR/bits	Dotted-decimal	Hexadecimal	Binary	Hosts
/17	255.255.128.0	ff ff 80 00	11111111 11111111 10000000 00000000	32,768
/18	255.255.192.0	ff ff c0 00	11111111 11111111 11000000 00000000	16,384
/19	255.255.224.0	ff ff e0 00	11111111 11111111 11100000 00000000	8,192
/20	255.255.240.0	ff ff f0 00	11111111 11111111 11110000 00000000	4,096
/21	255.255.248.0	ff ff f8 00	11111111 11111111 11111000 00000000	2,048
/22	255.255.252.0	ff ff fc 00	11111111 11111111 11111100 00000000	1,024
/23	255.255.254.0	ff ff fe 00	11111111 11111111 11111110 00000000	512
/24	255.255.255.0	ff ff ff 00	11111111 11111111 11111111 00000000	256
CIDR/bits	Dotted-decimal	Hexadecimal	Binary	Hosts
/25	255.255.255.128	ff ff ff 80	11111111 11111111 11111111 10000000	128
/26	255.255.255.192	ff ff ff c0	11111111 11111111 11111111 11000000	64
/27	255.255.255.224	ff ff ff e0	11111111 11111111 11111111 11100000	32
/28	255.255.255.240	ff ff ff f0	11111111 11111111 11111111 11110000	16
/29	255.255.255.248	ff ff ff f8	11111111 11111111 11111111 11111000	8
/30	255.255.255.252	ff ff ff fc	11111111 11111111 11111111 11111100	4
/31	255.255.255.254	ff ff ff fe	11111111 11111111 11111111 11111110	2
/32	255.255.255.255	ff ff ff ff	11111111 11111111 11111111 11111111	1
CIDR/bits	Dotted-decimal	Hexadecimal	Binary	Hosts

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