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mediumaddressing~35 min

Carve a /24 to fit four departments

One 10.20.0.0/24 block, four departments with very different sizes. A flat equal split doesn't fit. Design a VLSM plan that sizes each subnet to its host count.

Scenario

You're given one block, 10.20.0.0/24, and a router with four interfaces, one per department. The departments need very different numbers of hosts, so an equal split wastes space and may not even fit. Use VLSM: size each subnet to its department.

Requirements

  • eth1: Sales, ~50 hosts
  • eth2: Support, ~25 hosts
  • eth3: Ops, ~10 hosts
  • eth4: the point-to-point uplink, 2 hosts

The starter splits the block into four equal /26s, which is the wrong shape (and only barely fits).

Your job

In r1/frr.conf, assign each interface an address so its subnet is the smallest prefix that fits its host count, all inside 10.20.0.0/24, with no overlaps.

What "done" looks like

Each connected subnet is the smallest prefix that fits its department, all inside the block, with none overlapping.

Teaches: variable-length subnet masking. Allocate largest-first and size each subnet to its host count so the block isn't wasted.

What gets checked

Your solution is verified against each of these:

  • Every subnet sits inside 10.20.0.0/24
  • Each subnet is the smallest prefix that fits its department's host count
  • No two subnets overlap

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