Subnetting the Fast Way
8:10Coming soon
A company moves into a new building with one network, 192.168.1.0/24, and four departments that each want their own subnet. What mask, and where does Finance start? This lesson is subnetting the fast way: borrow bits from the host part, count the subnets and the hosts, list the networks and broadcasts, and answer the two exam questions in your head with the same three steps you used to read a single address.
You'll learn
- Borrowing bits: every bit you take from the hosts doubles the subnets and halves the block size (/25 → 2 × 128, /26 → 4 × 64, /27 → 8 × 32)
- Listing the subnets: they start at the multiples of the block size (.0, .64, .128, .192) and each ends one short of the next (.63, .127, .191, .255)
- Hosts per subnet: block size minus two, for the network address and the broadcast (64 → 62, 32 → 30, 16 → 14, 8 → 6)
- The other exam flavour: "at least 25 hosts per subnet" → the smallest block that fits (/27) keeps the most subnets for later
- Which subnet is this host on? 192.168.1.44 with 255.255.255.248 → 192.168.1.40/29, hosts .41–.46, broadcast .47, and why the same host under a /28 lands on .32
- The real thing: the router's interface table, one row per subnet, the router at the first usable address of each, and ipconfig on a host checked with the three steps
- Exam corner: at least five subnets with at least 25 hosts each from a /24 — which mask?
Chapters
- 0:00The new building
- 0:35Cutting a street: borrowing lamps
- 1:33The four-street cut
- 2:44The other way round: "at least this many houses"
- 3:53Which street is this house on?
- 5:02The real names
- 5:55The real thing: the router's interface table
- 7:05Exam corner
- 7:32Recap and next time
Exam objectives: CompTIA Network+ N10-009: 1.7 (IPv4 subnetting: CIDR, prefix length, subnet masks, number of subnets and hosts), 5.2 (incorrect subnet mask), 5.5 (ipconfig).
Byte City is not affiliated with or endorsed by CompTIA.