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CCNA QUICK REFERENCE

IPv4 Cheat Sheet

Subnet boundaries, masks, ranges, private space, and a repeatable exam method.

The five-step subnet method

  1. Convert prefix to mask.
  2. Find the interesting octet.
  3. Calculate block size: 256 − mask value.
  4. Locate the nearest lower block boundary.
  5. Network = boundary; broadcast = next boundary − 1.

Common prefixes

PrefixMaskTotalUsable*/24255.255.255.0256254/25255.255.255.128128126/26255.255.255.1926462/27255.255.255.2243230/28255.255.255.2401614/29255.255.255.24886/30255.255.255.25242
*Conventional host-subnet calculation. `/31` has special point-to-point use and `/32` identifies one host route.

Private ranges

10.0.0.0/8
10.0.0.0–10.255.255.255

172.16.0.0/12
172.16.0.0–172.31.255.255

192.168.0.0/16
192.168.0.0–192.168.255.255

Special-use traps

127.0.0.0/8 loopback

169.254.0.0/16 link-local/APIPA

224.0.0.0/4 multicast

255.255.255.255 limited broadcast

Host capacity

Host bits = 32 − prefix

Total addresses = 2host bits

Usable hosts = total − 2

Choose the smallest prefix that meets the requirement.

SUBNET DRILL // UNLIMITED CHALLENGES

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