On Monday, all company employees report being unable to connect to the corporate wireless network,
which uses 802.1x with PEAP. A technician verifies that no configuration changes were made to the
wireless network and its supporting infrastructure, and that there are no outages.
Which of the following is the MOST likely cause for this issue?

A.
Too many incorrect authentication attempts have caused users to be temporarily disabled.

B.
The DNS server is overwhelmed with connections and is unable to respond to queries.

C.
The company IDS detected a wireless attack and disabled the wireless network.

D.
The Remote Authentication Dial-In User Service server certificate has expired.

Explanation:
The question states that the network uses 802.1x with PEAP. The 802.1x authentication server is typically
an EAP-compliant Remote Access Dial-In User Service (RADIUS). A RADIUS server will be configured with a
digital certificate. When a digital certificate is created, an expiration period is configured by the Certificate
Authority (CA). The expiration period is commonly one or two years.
The question states that no configuration changes have been made so it’s likely that the certificate has
expired.
Incorrect Answers:
A: The question asks for the most likely cause of the issue. It’s very unlikely that all the users have
forgotten their passwords on the same day to cause too many incorrect authentication attempts and
caused users to be temporarily disabled.
B: The question asks for the most likely cause of the issue. A DNS server can usually handle thousands of
DNS requests. Even if a DNS server was overwhelmed, the users would still be able to connect to the
wireless network.C: The question asks for the most likely cause of the issue. The company IDS detected a wireless attack
and disabled the wireless network is very unlikely.

https://technet.microsoft.com/en-us/library/cc759077%28v=ws.10%29.aspx