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Subnet Masks Table

A subnet mask table can be handy when we need to calculate to the size of subnets with different prefix lengths or subnet masks. The following table lists out CIDR subnet masks along with the decimal equivalents and includes the total number of addresses as well as the total number of host addresses for each subnet mask.

CIDR Decimal # addresses # hosts
/0 0.0.0.0 4294967296 4294967294
/1 128.0.0.0 2147483648 2147483646
/2 192.0.0.0 1073741824 1073741822
/3 224.0.0.0 536870912 536870910
/4 240.0.0.0 268435456 268435454
/5 248.0.0.0 134217728 134217726
/6 252.0.0.0 67108864 67108862
/7 254.0.0.0 33554432 33554430
/8 255.0.0.0 16777216 16777214
/9 255.128.0.0 8388608 8388606
/10 255.192.0.0 4194304 4194302
/11 255.224.0.0 2097152 2097150
/12 255.240.0.0 1048576 1048574
/13 255.248.0.0 524288 524286
/14 255.252.0.0 262144 262142
/15 255.254.0.0 131072 131070
/16 255.255.0.0 65536 65534
/17 255.255.128.0 32768 32766
/18 255.255.192.0 16384 16382
/19 255.255.224.0 8192 8190
/20 255.255.240.0 4096 4094
/21 255.255.248.0 2048 2046
/22 255.255.252.0 1024 1022
/23 255.255.254.0 512 510
/24 255.255.255.0 256 254
/25 255.255.255.128 128 126
/26 255.255.255.192 64 62
/27 255.255.255.224 32 30
/28 255.255.255.240 16 14
/29 255.255.255.248 8 6
/30 255.255.255.252 4 2
/31 255.255.255.254 2 0
/32 255.255.255.255 1 -

Generally, while working as a network administrator or a network engineer you will mostly be working with networks of size /21 to /32. However, you may sometimes be working with larget networks (/16 to /20). You will seldom come across larger networks in practice (unless you work for a large service provider).

For this reason, it is good to be familiar with the details of /21 - /32 networks. The more familiar you are with networks of these sizes, the more comfortable you will be at your job.

IPv4 addressing and subnetting is covered in detail in this course: Course 2 - IP Addressing and Subnetting

Want to test your networking skills with hands-on configuration and troubleshooting questions? Try out the free Workshops section of this website here: Workshops (Login required).

Read how to use the device simulators on this website here: Workshops - General Instructions

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