CAS-003 · Question #795
A security engineer is troubleshooting an issue in which an employee is getting an IP address in the range on the wired network. The engineer plus another PC into the same port, and that PC gets an…
The correct answer is A. The company is using 802.1x for VLAN assignment, and the user or computer is in the wrong. The key diagnostic finding is that the problem follows the employee's PC regardless of whether it is connected via wired or wireless - another PC plugged into the same wired port gets a correct IP, ruling out a port or DHCP server issue. The fact that the PC is not receiving an…
Question
A security engineer is troubleshooting an issue in which an employee is getting an IP address in the range on the wired network. The engineer plus another PC into the same port, and that PC gets an IP address in the correct range. The engineer then puts the employee' PC on the wireless network and finds the PC still not get an IP address in the proper range. The PC is up to date on all software and antivirus definitions, and the IP address is not an APIPA address. Which of the following is MOST likely the problem?
Options
- AThe company is using 802.1x for VLAN assignment, and the user or computer is in the wrong
- BThe DHCP server has a reservation for the PC's MAC address for the wired interface.
- CThe WiFi network is using WPA2 Enterprise, and the computer certificate has the wrong IP
- DThe DHCP server is unavailable, so no IP address is being sent back to the PC.
How the community answered
(38 responses)- A79% (30)
- B5% (2)
- C13% (5)
- D3% (1)
Explanation
The key diagnostic finding is that the problem follows the employee's PC regardless of whether it is connected via wired or wireless - another PC plugged into the same wired port gets a correct IP, ruling out a port or DHCP server issue. The fact that the PC is not receiving an APIPA address means DHCP is responding, but the IP is from the wrong range, which maps to the wrong VLAN. 802.1x authenticates the device or user identity and dynamically assigns them to a VLAN based on group membership in a directory (e.g., Active Directory). If the user or computer account is in the wrong group or OU, 802.1x places them in the wrong VLAN, and that VLAN's DHCP scope delivers an IP in an unexpected range. This behavior is identity-bound, explaining why it persists across both wired and wireless connections.
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