Sharing One Broadband Line Across Three Training Rooms
A private IT training centre has 50 devices: 20 desktops in Room A, 15 desktops in Room B, and 15 laptops in Room C that connect over Wi-Fi. The centre has one broadband router with four LAN ports, a 16-port unmanaged switch in Room A, an 8-port unmanaged switch in Room B, and the router’s built-in Wi-Fi for Room C. The wiring is: router LAN port 1 → Room A switch; Room A switch port 16 → Room B switch port 8. All devices use static addresses in 192.168.1.0/24; the router’s DHCP pool is 192.168.1.100–192.168.1.150. Two staff laptops show “duplicate IP address” warnings. Room B loses connectivity whenever the Room A switch is restarted. Wi-Fi in Room C drops when more than 8 laptops connect, and file sharing between Room A and Room B sometimes fails. The centre cannot afford a new router but can buy one additional switch or access point if justified.
1. Calculate the wired port requirement and recommend the minimum additional device. Justify the choice.
Read the worked answer
Wired desktops = 20 + 15 = 35. Room A’s 16-port switch must also carry the uplink to the router and the uplink to Room B, so only 14 ports remain for 20 PCs-short by 6. Room B’s 8-port switch has one uplink, leaving 7 ports for 15 PCs-short by 8. The existing switches cannot cover 35 wired PCs even if the daisy chain is kept.
Buy one 24-port unmanaged switch for Room A: 20 PCs + router uplink + Room B uplink = 22 ports, leaving 2 spare. Move the existing 16-port switch to Room B: 15 PCs + uplink = 16 ports exactly, so use the 8-port as a spare or for a printer. This is the minimum single purchase that fixes both rooms. A single access point would not fix the missing wired ports; it should be the next request for Room C, because the router’s Wi-Fi is already dropping at 8 laptops.
2. Diagnose the duplicate IP warnings and propose an addressing plan that keeps static devices and DHCP from colliding.
Read the worked answer
The DHCP pool is 192.168.1.100–150, but staff have assigned static addresses inside that same range. Sooner or later the router leases an address that a staff laptop already uses, or two staff members copy the same static address. The warning confirms a conflict, and file sharing “sometimes” fails because one of the conflicting machines loses connectivity.
Plan: keep the router as DHCP server, but reserve a static block outside the pool, e.g. 192.168.1.2–99 for servers, printers and staff laptops, and 192.168.1.100–199 for DHCP. Use DHCP reservations (static lease by MAC) for staff laptops instead of manual configuration where possible. Document every static address in a register, and check with ipconfig /all and arp -a before assigning. If a conflict appears, release/renew the DHCP client and correct the duplicate static host.
3. Explain why Room B loses connectivity when the Room A switch restarts, and why Room C Wi-Fi drops above 8 laptops. Give one fix for each.
Read the worked answer
Room B is daisy-chained through Room A: router → Room A switch → Room B switch. When the Room A switch reboots, the uplink to Room B goes down, so Room B is isolated until Room A returns. That is a single point of failure, not a separate fault. Fix: use one of the router’s spare LAN ports to feed Room B directly (router LAN 2 → Room B switch), so the two rooms have independent uplinks; the 24-port switch can still serve Room A.
Room C’s Wi-Fi drop is likely client limit/congestion: a consumer router’s Wi-Fi may handle about 8 active laptops poorly, especially on 2.4 GHz with interference. Fix: add a wired access point in Room C, use 5 GHz where possible, separate SSIDs, and channel planning; if only one purchase is allowed, the switch is still the priority for 35 wired PCs, but the AP should be requested next.