Diagnosing Address Conflicts in a 30-Computer School Lab
The computer lab of a higher secondary school has 30 Windows PCs, one broadband router with four LAN ports, two 24-port unmanaged switches connected to each other, one network printer and a teacher laptop. The ISP supplies one public IP address. Over the years teachers configured addresses by hand: some PCs use 192.168.1.10 to 192.168.1.40, others use 10.0.0.10 to 10.0.0.20; some have default gateway 192.168.1.1 and others 10.0.0.1. This week two PCs report an IP address conflict, several PCs cannot reach the internet, and the printer is reachable only from the PCs in the same room. The school plans to add 10 borrowed laptops for a two-day workshop. The teacher asks whether to buy another router or another switch, and whether every PC should be given a static IP so that the lab is stable.
1. Diagnose the symptoms. Propose one addressing scheme for the 30 PCs, the printer, the teacher laptop and the 10 workshop laptops, including subnet mask, gateway and allocation method.
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Two different private subnets, 192.168.1.0/24 and 10.0.0.0/8, are mixed on the same flat LAN. Hosts with the wrong gateway cannot reach the router, and hosts on different subnets cannot reach each other or the printer without routing. The duplicate static addresses explain the IP conflict. A single subnet solves all three symptoms. The lab needs about 42 addresses, so 192.168.1.0/26 with mask 255.255.255.192 provides 62 usable addresses and is sufficient, or 192.168.1.0/24 can be used if simplicity and future growth matter more than address conservation. Use the router LAN address 192.168.1.1 as the only default gateway on every device. Enable DHCP on the router for student PCs and workshop laptops, with a pool such as 192.168.1.10 to 192.168.1.50. Give the printer a DHCP reservation or a static address outside the pool, for example 192.168.1.5, and do the same for the teacher laptop if it needs a stable address. Document the plan and remove the old 10.0.0.x settings.
2. Should the school buy another router or another switch for the workshop laptops? Explain what each device would do in this network.
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A switch is the appropriate purchase if more ports are needed. A switch extends the same local network at layer 2, so all PCs, the printer and the new laptops remain in one subnet and can reach each other directly. The existing router already provides the single connection to the ISP and performs NAT for the public address. Adding a second router would create another subnet and another NAT boundary. Devices on the new router's LAN would not be reachable from the existing lab without routing, port forwarding or double NAT, which would make the printer and file sharing more complicated. The existing two unmanaged switches may already have enough free ports; the school should count active ports before buying anything. A second router would be justified only if the school deliberately wanted a separate guest network with isolation, and even then a router or access point designed for that role should be configured properly.
3. The teacher wants every PC to have a static IP for stability. Advise on static versus DHCP, including what should still be static or reserved.
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Static addresses on every student PC are the likely cause of the current conflict and will make the workshop harder. DHCP is more stable in practice because it prevents duplicate addresses and automatically configures the gateway and DNS server. The router or a server should hold the DHCP pool, and the pool must exclude any addresses used for reservations. Devices that provide a service and need a predictable address, such as the printer, should have a DHCP reservation or a static address outside the pool. The teacher laptop can also have a reservation if it needs consistent access. Student PCs and the 10 borrowed laptops should use DHCP. If static addressing is required for a specific practical, restrict it to a documented range and disable DHCP on those devices only, rather than mixing static and dynamic addresses unpredictably.