Five segments, one /23
A warehouse, an office, a voice VLAN, a DMZ and a router link all have to fit in 172.16.4.0/23 with no overlap and no waste. Design the VLSM plan, apply it, and route between the segments.
Scenario
A distribution site got the block 172.16.4.0/23 and five segments to fit into it:
- Warehouse floor: needs 200 hosts
- Office: needs 100 hosts
- Voice VLAN: needs 40 hosts
- DMZ: needs 10 hosts
- Router-to-router link: needs 2 usable addresses
Design a VLSM plan that fits all five into the /23 with no overlap and no waste: each
subnet sized to the smallest prefix that works. Apply it, and prove every segment reaches every
other.
Topology
- R1 hosts the warehouse and office segments and links to R2.
- R2 hosts the voice and DMZ segments.
- One host sits on each LAN segment. Interfaces start unaddressed: the addressing is yours to design and apply.
Your job
Produce the plan (largest segment first), apply it to the router interfaces, and add the static routes so all four LAN segments reach each other across the link.
What "done" looks like
A clean, non-overlapping plan from 172.16.4.0/23 with the smallest prefix per segment, applied,
with full reachability between segments.
Teaches: VLSM at a size where sloppy allocation actually runs out of space: a /23 holds these five segments only if the big blocks land first.
What gets checked
Your solution is verified against each of these:
- Each segment uses the smallest prefix that fits its host count, all inside 172.16.4.0/23
- No two subnets in the plan overlap
- Hosts on all four LAN segments can reach each other
Solve it in the browser lab
No setup, no install. Open a live lab: configure each device in the editor or its Cisco IOS terminal, run show/ping/traceroute (or test from the hosts), and watch the network react. The in-house engine grades your fix instantly and issues your proof the moment every check passes.
Open the lab →Prefer your own lab?
- Build the fix locally. New to the tooling? See setting up your lab.
- Push your topology file, device configs, and any playbooks to a public repo (GitHub or GitLab).
- Submit the repo link. We review it by hand, confirm it works, and issue your proof page.