Examkin

Question

Difficulty: MediumIP Addressing Services

A network technician is deploying a new remote office client subnet (VLAN 40). Hosts connected to VLAN 40 are unable to reach the centralized DHCP server located across a Layer 3 WAN link at IP address 10.10.1.50, causing client machines to automatically receive 169.254.x.x addresses. Which of the following configuration actions on the router's VLAN 40 gateway interface will resolve this issue?

  1. Configure an IP helper address specifying the destination IP 10.10.1.50.Answer
  2. B
    Create an AAAA DNS resource record pointing the gateway hostname to 10.10.1.50.
  3. C
    Change the default gateway DHCP relay setting from UDP port 67 to TCP port 67.
  4. D
    Configure the IP helper address to point to the local interface APIPA network address.

Answer

Configure an IP helper address specifying the destination IP 10.10.1.50.
Because Layer 3 routers block broadcast messages by default, host DHCP DISCOVER broadcasts generated on VLAN 40 cannot reach a DHCP server residing on a different subnet. Setting an IP helper address on the router's local gateway interface acts as a DHCP Relay Agent, converting client broadcasts into directed unicast packets to IP 10.10.1.50.

Step-by-Step Solution

1
Identify the cause of client address allocation failure.
Clients on VLAN 40 generate APIPA addresses because local DHCP broadcast frames (DISCOVER) cannot traverse the Layer 3 router boundary to reach the central DHCP server.
Routers drop Layer 2/3 broadcast packets by default.
2
Determine the required service to enable cross-subnet DHCP functionality.
Deploying a DHCP Relay Agent (IP Helper) on the incoming default gateway interface intercepts broadcast traffic.
The relay agent wraps broadcast DISCOVER messages into unicast IP packets directed to the designated DHCP server address.
3
Select the correct interface configuration command.
Applying the IP helper address command pointing to 10.10.1.50 enables unicast forwarding of DHCP traffic across the WAN link.
This allows clients to successfully complete the DORA process and acquire valid IP leases from the central scope.

Key Concept

DHCP Relay / IP Helper Operation across Layer 3 Boundaries
Rate this question

Topics

IP Addressing Services

More questions from this topic