A network administrator is troubleshooting connectivity issues on a corporate wireless gue… — CompTIA Network+

A network administrator is troubleshooting connectivity issues on a corporate wireless guest network spanning the $192.168.100.0/24$ subnet. Transient users report that their laptops periodically fail to connect to network resources and receive self-assigned IP addresses in the $169.254.0.0/16$ range during peak operating hours. Upon inspecting the central DHCP server status, the administrator observes the following command output snippet:

text
DHCP Scope: Guest_VLAN100
Subnet Prefix: 192.168.100.0/24
Range: 192.168.100.10 - 192.168.100.250
Total Scope Addresses: 241
Active Leases: 241 (100% utilized)
Pending Requests: 14 (Dropped - No available addresses)
Lease Duration: 8 days 00:00:00

Physical attendance logs confirm that no more than 60 guest users are ever present in the facility concurrently. Which of the following is the most likely root cause of this issue?

The DHCP lease duration is configured too long for a network with high host turnover, leading to scope exhaustion.Answer
B
The default gateway interface on the Layer 3 switch is down, causing clients to immediately default to APIPA addresses.
C
The DHCP relay agent is dropping DHCPDISCOVER packets because the helper address points to an incorrect default gateway.
D
The network administrator miscalculated the usable host capacity of the subnet by failing to subtract the network and broadcast addresses.

Answer

The most likely root cause is that the DHCP lease duration is configured too long for a network with high host turnover, leading to scope exhaustion.

The correct answer identifies that an excessively long DHCP lease time (8 days) on a transient network (guest Wi-Fi) leads to scope exhaustion. Even though concurrent user count is low, new MAC addresses consume IP allocations that are retained long after devices leave the network.

Step-by-Step Solution

Analyze the client symptom

Clients receive

169.254.x.x

(APIPA) addresses, indicating a failure to receive a DHCP response during the DORA process.

When a host sends a DHCPDISCOVER and receives no DHCPOFFER, operating systems fall back to Automatic Private IP Addressing.

Examine the DHCP server log output

Active leases equal

241

out of

241

(

100\%

utilization), and

14

pending requests are dropped due to no available addresses.

The server scope is completely exhausted, preventing new DHCPOFFER messages from being issued.

Correlate scope metrics with environment characteristics

The physical presence is only ~60 concurrent users, but the lease duration is set to 8 days.

Transient devices connect, lease an IP, and leave. Because the lease lasts 8 days, old MAC bindings remain occupied in state memory long after devices depart, accumulating 241 assigned leases over time.

Key Concept

DHCP Scope Exhaustion and Lease Time Optimization

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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