Fifteen PCs, Two Switches and a Broken Name Lookup
A school lab has 15 desktop computers, one broadband router with four LAN ports and Wi-Fi, and two 8-port unmanaged switches. The router's DHCP range is 192.168.1.100 to 192.168.1.150. Ten tablets connect over Wi-Fi. On Monday, the teacher's laptop receives 192.168.1.107, but PC-7 and PC-11 show 169.254.18.4 and 169.254.18.9. On PC-7, ping 8.8.8.8 succeeds, but the browser reports “Server not found” for every website. On PC-11, the school website opens when its numeric address 203.0.113.10 is typed, but not by name. The shared printer on PC-4 is not visible from PC-7. The lab has no network diagram and cables run under floor mats.
1. Diagnose the addressing problem on PC-7 and PC-11 and the browser problem on both machines.
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The 169.254.x.x addresses are APIPA addresses. A computer gives itself one when it cannot reach a DHCP server, so PC-7 and PC-11 are not receiving addresses from the router. Because the teacher's laptop gets 192.168.1.107, DHCP works on the Wi-Fi or on that cable, so the fault is likely in the two PCs' cables, switch ports, or network adapter settings - not the router as a whole. Check link lights, swap cables and ports, and confirm that both PCs are set to obtain an IP address automatically.
The browser symptom is separate: ping to 8.8.8.8 succeeds, so IP connectivity and routing work, but name resolution fails. Typing 203.0.113.10 works, which confirms the web server is reachable. The likely cause is a wrong or missing DNS server address, or a DNS service problem. Set DNS to the router or a reliable public resolver, then run ipconfig /flushdns and test with nslookup. On PC-7, the APIPA address must be fixed before DNS can work properly.
2. Propose a simple IP plan and cabling layout, and give a test sequence to confirm the repair.
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Keep one flat private network for simplicity:
- Router LAN address 192.168.1.1, subnet mask 255.255.255.0.
- DHCP range 192.168.1.100–192.168.1.150 for laptops, tablets and phones.
- Reserve 192.168.1.10–192.168.1.30 for the 15 desktops and the printer, either as static addresses or DHCP reservations.
- Connect router → switch 1 → switch 2; avoid loops and do not use a crossover cable where the equipment auto-senses.
Cabling: label both ends of every cable, keep runs away from power lines and water, use cable ties rather than tight knots, and replace cables under mats with proper trunking. Record the layout in a simple diagram with port numbers.
Test sequence: link light → IP address in the correct range → ping the gateway → ping 8.8.8.8 → ping a name such as the school website → open the website in a browser. Test one PC at a time so a failure is easy to localise.
3. Why can PC-7 not see the printer on PC-4, and what should be done? Include one Wi-Fi security measure.
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Printer sharing depends on more than an IP address. PC-4 must have File and Printer Sharing enabled, the printer must be marked as shared with a share name, and PC-7 must be in the same workgroup or be able to authenticate to PC-4. Windows Firewall may block sharing on a “Public” network profile, and the two PCs may be on different network profiles even though they are on the same subnet. PC-7's APIPA address would also prevent it from reaching PC-4's 192.168.1.x address.
Fix the addressing first, then set the network profile to Private, enable sharing, and add the printer on PC-7 using \\PC-4\printername or the Add Printer wizard. Confirm permissions and print a test page.
For Wi-Fi, use WPA2 or WPA3 rather than open or WEP security, change the router's default administrator password, and keep the admin interface off the student network. Do not share the Wi-Fi password publicly; create a separate guest network if visitors need access.