If subnetting questions feel slow, start with the subnet boundaries rather than converting every address from scratch. For a conventional IPv4 /27 subnet, five host bits remain. That creates 32 addresses per subnet, normally with one network address, one broadcast address and 30 usable host addresses.
This article uses original arithmetic examples for study. They are not copied Cisco exam items. Check the current Cisco CCNA training scope when deciding how subnetting fits into the rest of your networking preparation.
Work through 192.168.10.77/27
The /27 mask is 255.255.255.224. In the final octet, subnet starts occur every 32 addresses: 0, 32, 64, 96, 128, 160, 192 and 224.
The address 77 lies between 64 and 95. Therefore:
- Network address: 192.168.10.64.
- Broadcast address: 192.168.10.95.
- Conventional usable host range: 192.168.10.65 through 192.168.10.94.
The next subnet starts at 96, so its preceding address, 95, is the broadcast address for this subnet. This is a boundary calculation, not a guess based on the address ending in a familiar number.
Check whether a proposed host belongs
A question might offer 192.168.10.96 as another host in the same subnet. It does not belong: 96 begins the next /27 block. Another option might be 192.168.10.95. That address is inside the block but is its broadcast address, not a conventional host assignment.
These are different errors. “Outside the subnet” and “reserved address within the subnet” should have different explanations in your review notes.
Use the CCNA subnetting practice questions to practice identifying the requested quantity before calculating. A question asking for a network address is not asking for the first usable host, even though those addresses are adjacent.
Try a second block without the answer first
For 172.16.4.201/27, which block contains the host? The boundaries remain multiples of 32 in the final octet. The containing block begins at 192 and ends at 223, giving a conventional usable range from 193 through 222.
Verify the answer by checking the next boundary, 224, and by counting 32 addresses inclusively from 192 through 223. Two independent checks are more useful than repeatedly rereading your first calculation.
Build a compact reference you can reconstruct
On your own review page, write three items for /27: mask 224 in the relevant octet, block size 32 and five host bits. Then derive the answers for an unfamiliar address. The CCNA subnetting quick reference is useful for revisiting those relationships after a missed question.
Keep the scope of the shortcut clear. This example describes ordinary IPv4 subnets; special /31 point-to-point and /32 cases should not be forced into the same “subtract two” rule. A strong subnetting method includes knowing when the method applies.