Appendix A. Subnetting Class A

Subnetting Class A

Let's start by listing all the Class A masks:

255.0.0.0    (/8)
255.128.0.0  (/9)           255.255.240.0  (/20)
255.192.0.0  (/10)          255.255.248.0  (/21)
255.224.0.0  (/11)          255.255.252.0  (/22)
255.240.0.0  (/12)          255.255.254.0  (/23)
255.248.0.0  (/13)          255.255.255.0  (/24)
255.252.0.0  (/14)          255.255.255.128  (/25)
255.254.0.0  (/15)          255.255.255.192  (/26)
255.255.0.0  (/16)          255.255.255.224  (/27)
255.255.128.0  (/17)        255.255.255.240  (/28)
255.255.192.0  (/18)        255.255.255.248  (/29)
255.255.224.0  (/19)        255.255.255.252  (/30)

That's it. You must leave at least 2 bits for defining hosts. And I hope you can see the pattern by now. Remember, we're going to ...

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