Coaching Centre LAN and a Fake Result Link
A coaching centre has 12 desktop PCs, one broadband router at 192.168.1.1 with subnet mask 255.255.255.0, and a shared printer with static address 192.168.1.200. The router's DHCP pool is 192.168.1.100 to 192.168.1.150. Staff laptops use the staff Wi-Fi; students use a separate guest Wi-Fi. A staff laptop receives 192.168.1.160 and can browse the Internet but cannot print or open the printer's web page. Another staff laptop receives 192.168.1.100 and prints normally. Separately, several students received a WhatsApp message: “Check WBBSE result at wbbse-result-check.net - enter roll number and OTP.” Three students entered their roll numbers and one entered an OTP before a teacher intervened. The centre wants a technical fix for the laptop and a response plan for the students.
1. Diagnose why the laptop at 192.168.1.160 cannot reach the printer, even though Internet access works. Give an ordered set of checks and a practical fix.
Read the worked answer
The address 192.168.1.160 is in the same /24 subnet as the printer, so this is not a basic subnet-mask mismatch. But it is outside the stated DHCP pool (.100–.150), which suggests the laptop either has a manually assigned address, received a lease from a second DHCP server, or is connected through a different access point that uses the same address range.
Order of checks:
- Run ipconfig /all on the laptop: record IP address, subnet mask, default gateway and DHCP server. If the DHCP server is not 192.168.1.1, a second router or guest network is involved.
- Confirm which Wi-Fi SSID the laptop has joined. Guest networks often enable client isolation, which blocks access to the wired printer while still allowing Internet traffic.
- Ping 192.168.1.200 from the laptop. If ping fails, check the printer's own network settings and whether it is online.
- Try opening the printer's web page from the working laptop; compare results.
Practical fix: if the laptop is on the guest SSID, connect it to the staff SSID. If it is on the staff network but has a static address, change it to automatic DHCP or assign a documented address outside the DHCP pool but away from the printer. Avoid simply giving it .200, which is already the printer.
2. Assess the WhatsApp message. What evidence suggests phishing, and what should the centre tell the three students to do immediately?
Read the worked answer
The message has several phishing indicators: an unofficial-looking domain rather than the official board site, a request for an OTP, urgency about results, and circulation through WhatsApp rather than a known portal. A result-check site normally needs a roll number and date of birth or similar; it does not need a one-time password that could authorise a separate account action.
Immediate advice to the three students:
- Do not enter any more data, and do not forward the link.
- If an OTP was entered, treat the associated account or phone number as exposed; change the password of any account that uses that number and enable two-factor authentication where possible.
- Report the link to the teacher and to the appropriate cybercrime reporting channel; preserve screenshots.
- Tell the centre's IT contact so that the link can be blocked on the centre network and other students warned.
The centre should not try to “test” the link by entering fake data, because that can still expose the device and confirm the link is active.
3. Should the printer's static address be moved inside the DHCP pool? Explain the trade-off and give a recommendation for this centre.
Read the worked answer
No. A static device such as a printer should sit outside the DHCP pool, otherwise the router could lease the same address to a laptop and cause an address conflict. The current choice of .200, outside .100–.150, is correct.
The trade-off is documentation: an address outside the pool must be recorded and reserved in the router if possible. The centre should either add a DHCP reservation for the printer or keep a simple address register. The pool itself has 51 addresses; with 12 desktops, staff laptops and phones, that is workable but not generous, so unused leases should expire and guest devices should remain on the guest network. The fix for the .160 laptop is therefore not to enlarge the pool blindly, but to find why that laptop bypassed the expected DHCP range.