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Difficulty: MediumTroubleshooting IP Addressing and DHCP Services

A network technician is troubleshooting a newly installed server connected to VLAN 50 (192.168.50.0/24192.168.50.0/24). The server is configured to obtain IP settings dynamically but continually configures an IP address of 169.254.112.45169.254.112.45. The organization's centralized DHCP server is located on VLAN 10 (192.168.10.5192.168.10.5) and correctly services hosts on VLAN 10. Which of the following root causes and remediation steps accurately address this connectivity issue? (Select TWO.)

  1. The router interface servicing VLAN 50 lacks a DHCP relay agent configuration, preventing broadcast DHCP requests from reaching the server on VLAN 10.Answer
  2. An IP helper address pointing to 192.168.10.5 must be configured on the VLAN 50 default gateway interface.Answer
  3. C
    The server failed to obtain an IP address because its static default gateway was configured on a different IP subnet than its 169.254.0.0/16 address.
  4. D
    The DHCP scope failed because a /24 subnet yields 256 usable host addresses and the pool reached maximum allocation capacity.

Answer

The server is receiving an APIPA address (169.254.112.45169.254.112.45) because DHCP broadcast traffic from VLAN 50 is not traversing the router to the DHCP server on VLAN 10. To resolve this, a DHCP relay agent (IP helper address pointing to 192.168.10.5192.168.10.5) must be configured on the router interface for VLAN 50.
DHCP clients issue Layer 2 broadcast requests during discovery. Because routers block Layer 2 broadcasts by default, devices on VLAN 50 cannot reach the DHCP server on VLAN 10 unless a DHCP relay agent is enabled. Configuring an IP helper address on the router interface servicing VLAN 50 converts these local broadcasts into targeted unicast traffic sent to 192.168.10.5, allowing the server on VLAN 50 to receive an IP lease.

Step-by-Step Solution

1
Analyze the IP address symptom (169.254.112.45169.254.112.45).
Recognize that the 169.254.0.0/16169.254.0.0/16 range represents APIPA, indicating the client sent DHCPDISCOVER requests but received no DHCP OFFER response.
When a DHCP client receives no response to its broadcast requests, the operating system self-assigns an APIPA address.
2
Examine the network topology boundaries between VLAN 50 and VLAN 10.
Identify that VLAN 50 (192.168.50.0/24192.168.50.0/24) and VLAN 10 (192.168.10.0/24192.168.10.0/24) are separated by a Layer 3 router.
Routers drop Layer 2 broadcast packets (like DHCPDISCOVER) by default unless explicitly configured to relay them.
3
Determine the required resolution to forward broadcast DHCP traffic across subnets.
Configure `ip helper-address 192.168.10.5` on the default gateway interface for VLAN 50.
The IP helper feature intercepts incoming DHCP broadcasts on the interface and unicasts them to the DHCP server IP specified.

Key Concept

DHCP Relay Agent (IP Helper) Operations and APIPA Diagnosis
Estimated Time:1m 30s
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Topics

Troubleshooting IP Addressing and DHCP Services

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