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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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