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Difficulty: MediumTroubleshooting IP Addressing and DHCP Services

A network administrator deploys a new workstation on VLAN 35 (10.35.0.0/2410.35.0.0/24). Upon booting up, the workstation cannot access internal servers or the internet. Executing `ipconfig /all` on the workstation yields the following output:

IPv4 Address. . . . . . . . . . . : 169.254.14.88
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . :
DHCP Enabled. . . . . . . . . . . : Yes

The central DHCP server is located on VLAN 10 (10.10.0.0/2410.10.0.0/24) and actively provides IP address leases to clients on VLAN 10. Which of the following represents the most likely cause of this issue?

  1. The Layer 3 interface serving VLAN 35 lacks an IP helper address pointing to the DHCP server.Answer
  2. B
    The workstation has been manually assigned an invalid static default gateway address.
  3. C
    The central DHCP server's scope pool for VLAN 10 has exhausted all available host IP addresses.
  4. D
    The workstation's default gateway resides on a different IP subnet than the host.

Answer

The Layer 3 interface serving VLAN 35 lacks an IP helper address pointing to the DHCP server.
The client address 169.254.14.88169.254.14.88 indicates that the workstation failed to receive a response to its DHCP DISCOVER broadcast and fell back to Automatic Private IP Addressing (APIPA). Because the DHCP server is on a different subnet (VLAN 10), the router interface serving VLAN 35 must be configured with a DHCP Relay Agent (`ip helper-address`) to forward client broadcast requests to the unicast IP address of the DHCP server.

Step-by-Step Solution

1
Analyze host network configuration output.
The workstation has an IPv4 address of 169.254.14.88169.254.14.88 with a /16/16 mask (255.255.0.0255.255.0.0) and no default gateway.
Addresses in the range 169.254.0.1169.254.0.1 through 169.254.255.254169.254.255.254 represent Automatic Private IP Addressing (APIPA), indicating the client tried and failed to contact a DHCP server.
2
Evaluate network topology and DHCP traffic flow boundaries.
The host is on VLAN 35 (10.35.0.0/2410.35.0.0/24), while the DHCP server resides on VLAN 10 (10.10.0.0/2410.10.0.0/24).
DHCP discovery messages are sent as Layer 2 broadcast packets (255.255.255.255255.255.255.255). Routers do not forward Layer 2 broadcasts across subnets by default.
3
Identify missing relay component.
A DHCP Relay Agent (such as `ip helper-address` on a router or Layer 3 switch interface) is required on VLAN 35 to forward broadcast requests as unicast packets to the DHCP server on VLAN 10.
Without an IP helper address configured on VLAN 35's default gateway interface, DHCP DISCOVER broadcasts are dropped by the router.

Key Concept

DHCP Relay Agent and APIPA Diagnosis
Estimated Time:1m 15s
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Topics

Troubleshooting IP Addressing and DHCP Services

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