Subnet Cheat Sheet

This is part of the Cisco Notes series on Mike’s World News.

I think one of the most important things to write down once you get into the testing center during the Cisco tutorial is your CIDR notation, with the # of hosts, and the full Subnet Mask.  I would go from /22 – /30, although that is my personal preference. 

CIDR Notation # of Hosts Subnet Mask
/30 4 (2 usable) 255.255.255.252
/29 8 (6 usable) 255.255.255.248
/28 16 (14 usable) 255.255.255.240
/27 32 (30 usable) 255.255.255.224
/26 64 (62 usable) 255.255.255.192
/25 128 (126 usable) 255.255.255.128
/24 (Class C) 256 (254 usable) 255.255.255.0
/23 512 (510 usable) 255.255.254.0
/22 1024 (1022 usable) 255.255.252.0
/21 2048 (2046 usable) 255.255.248.0
/20 4096 (4094 usable) 255.255.240.0
/19 8192 (8180 usable) 255.255.224.0
/18 16,384 (16,382 usable) 255.255.192.0
/17 32,768 (32,766 usable) 255.255.128.0
/16 (Class B) 65,536 (65,534 usable) 255.255.0.0
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