A network administrator is troubleshooting network connectivity for several newly installe… — CompTIA Network+

A network administrator is troubleshooting network connectivity for several newly installed point-of-sale (POS) terminals operating on VLAN 40 ( $192.168.40.0/24$ ). Executing `ipconfig /all` on an affected terminal displays an IPv4 address of $169.254.10.45$ with a subnet mask of $255.255.0.0$ and no default gateway specified. The centralized enterprise DHCP server is situated on VLAN 10 ( $10.1.10.5/24$ ), and existing clients on VLAN 10 acquire leases without error.

Which of the following are potential root causes for this issue? (Select TWO.)

The router or Layer 3 switch interface serving VLAN 40 lacks an IP helper address (DHCP relay agent) pointing to $10.1.10.5$ .Answer
The DHCP server scope corresponding to the $192.168.40.0/24$ network is exhausted or deactivated.Answer
C
The default gateway parameter configured on the POS terminal is set to an address on an incorrect IP subnet.
D
The client network adapter has a duplex mismatch with the connected switchport, preventing Layer 2 link initialization.

Answer

The potential root causes are: (1) The router/Layer 3 switch interface for VLAN 40 is missing an IP helper address pointing to the DHCP server on VLAN 10, and (2) The DHCP server scope for subnet 192.168.40.0/24 is exhausted or deactivated.

An APIPA address (

169.254.x.x

) signifies that the host generated its own IP address because it received no DHCP offer. In a multi-VLAN environment where the DHCP server is on a different subnet (VLAN 10), the router interface connecting VLAN 40 must have an IP helper address configured to relay DHCPDISCOVER broadcasts. Additionally, if the relay is functioning properly but the DHCP scope for VLAN 40 is disabled or full, the server will not return a DHCP lease.

Step-by-Step Solution

Analyze the client symptom from the terminal output.

The IP address 169.254.10.45 indicates Automatic Private IP Addressing (APIPA), which occurs when a DHCP client fails to receive a response to its DHCPDISCOVER broadcast.

Recognizing APIPA narrows the troubleshooting focus specifically to DHCP communication failure between the host and the DHCP server.

Evaluate cross-VLAN broadcast behavior and relay requirements.

Since the client resides on VLAN 40 and the server resides on VLAN 10, Layer 3 routers will drop unforwarded broadcast packets. An IP helper address must be configured on the VLAN 40 interface.

DHCP broadcast messages cannot cross router boundaries without explicit relaying configured.

Evaluate DHCP server state for the target subnet.

Even if relaying functions, a scope that is deactivated or depleted of IP addresses will fail to offer an IP lease to requesting clients.

Exhausted or disabled scopes prevent new leases from being issued.

Key Concept

Troubleshooting APIPA symptoms across routed VLAN boundaries (DHCP Relay and Scope Availability)

Estimated Time:1m 30s

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