CIDR and VLSM: Streets of Different Sizes
8:31Coming soon
The new building's headcount arrives: 100, 50, 20, 6 and 2. Four equal streets of 62 can't hold Sales and waste fifty houses on the switch closet, so this lesson cuts one network into streets of different sizes. The only new rule is the order: biggest first, each street the smallest that fits, each one starting on a multiple of its own width. Then the word on every sign: the slash is CIDR, classless means the sign decides, and five streets go into the crossroads as one.
You'll learn
- VLSM step by step: 100/50/20/6/2 from 192.168.1.0/24 → /25 .0, /26 .128, /27 .192, /29 .224, /30 .232, with twenty numbers spare
- Why biggest first works: every smaller street lands on a multiple of its own width for free
- The whole plan on one card: width, mask, slash, network, usable hosts and broadcast for all five subnets
- What CIDR means, and the old classes A, B and C the exam still names (and nobody builds with)
- Same address, three slashes, three different subnets: read the prefix, never the first octet
- Route summarisation: five subnets in, one 192.168.1.0/24 out at the crossroads
- The trap: 192.168.1.200/27 is not a valid network address, and the test that catches it
- The real thing: a router interface table with five different masks, and ipconfig on a /30 point-to-point link
- Exam corner: which of .200, .208, .224, .240 is a valid /27 network address
Chapters
- 0:00The headcount: four equal streets don't fit
- 1:01Biggest first: five streets, five sizes
- 2:06The plan: five streets, five masks
- 3:17What CIDR means: classes, then the slash
- 4:27Five streets in, one sign out
- 4:58The trap: a street on the wrong multiple
- 6:01The real names
- 6:43The real thing: five masks on one router
- 7:31Exam corner
- 7:56Recap and next time
Exam objectives: CompTIA Network+ N10-009: 1.7 (VLSM, CIDR notation, classful vs classless addressing, route summarisation basics), 5.2 (incorrect subnet mask), 5.5 (ipconfig).
Byte City is not affiliated with or endorsed by CompTIA.