In a corporate network using a Class C address scheme, what is a plausible cause for login failures when many users are connecting late in the day?

In a corporate network using a Class C address scheme, what is a plausible cause for login failures when many users are connecting late in the day?

• A. DHCP pool exhaustion
• B. Leases are set too long
• C. DNS issues
• D. Incorrect subnet mask

Answer: (A)

DHCP pool exhaustion is the most plausible cause. In a Class C subnet you have a limited number of IP addresses (up to 254 usable addresses) that the DHCP server can hand out. If a large number of users try to log in at the same time, the DHCP server may have already leased out most or all of those addresses. Without a free IP, a new device can’t complete network configuration, can’t reach authentication servers (like domain controllers), and login attempts fail because the device has no way to communicate on the network. If leases were set very long, the pool could become unavailable more quickly as devices hold onto addresses longer, but the root issue remains the finite pool and peak demand. DNS problems would show up as general name-resolution failures, not specifically tied to a late-day surge, and an incorrect subnet mask would cause broader connectivity issues for all devices, not just during peak sign-in times.

DHCP pool exhaustion is the most plausible cause. In a Class C subnet you have a limited number of IP addresses (up to 254 usable addresses) that the DHCP server can hand out. If a large number of users try to log in at the same time, the DHCP server may have already leased out most or all of those addresses. Without a free IP, a new device can’t complete network configuration, can’t reach authentication servers (like domain controllers), and login attempts fail because the device has no way to communicate on the network.

If leases were set very long, the pool could become unavailable more quickly as devices hold onto addresses longer, but the root issue remains the finite pool and peak demand. DNS problems would show up as general name-resolution failures, not specifically tied to a late-day surge, and an incorrect subnet mask would cause broader connectivity issues for all devices, not just during peak sign-in times.