Networking
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3 Subnetting Mistakes That Cost Marks
3 mistakes that cost marks in subnetting. Are you making one?
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Lesson notes
Key points
- Forgetting the minus 2: Students write 2^h as usable hosts; subtract two for network and broadcast addresses.
- Counting network bits as…: Using the prefix as host bits flips the answer; host bits are 32 minus the prefix.
- Assigning the broadcast…: Giving a device the last address breaks it; the highest usable host is broadcast minus one.
Takeaway: Host bits = 32 − prefix, then subtract 2 for usable hosts.
Quick check: In 192.168.1.0/24, what is the highest address you can give a host?
- 192.168.1.255
- 192.168.1.254
- 192.168.1.256
.255 is the broadcast address, so .254 is the last usable host.
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