Examkin

Question

Difficulty: MediumIP Addressing Services

Security audit logs indicate that endpoints located in a newly provisioned research laboratory segment (subnet 10.45.80.0/2410.45.80.0/24) are failing to receive dynamic IP address assignments. The organization maintains a centralized redundant DHCP server cluster at 10.45.10.5010.45.10.50. While unicast routing between the subnets is verified to be functioning properly, client broadcast DHCPDISCOVER messages originating from the laboratory segment are stopped at the local router interface. Which configuration change on the gateway router will allow the research segment endpoints to obtain dynamic IP leases from the central cluster?

  1. Adding the IP helper address pointing to 10.45.10.50 on the router interface serving subnet 10.45.80.0/24Answer
  2. B
    Adding the IP helper address pointing to 10.45.80.1 on the router interface directly connected to the DHCP server
  3. C
    Creating an authoritative CNAME record on the DNS server mapping the subnet broadcast address to 10.45.10.50
  4. D
    Reconfiguring the client endpoints to transmit DHCP discovery requests over TCP port 68 instead of UDP port 67

Answer

Configure the IP helper address pointing to 10.45.10.50 on the incoming router interface for subnet 10.45.80.0/24.
Routers do not forward Layer 2 or Layer 3 broadcast messages across subnet boundaries by default. When endpoints emit DHCPDISCOVER broadcasts on subnet 10.45.80.0/24, the router interface serving as their default gateway drops the broadcast. Configuring an IP helper address on that specific incoming interface enables the router to act as a DHCP Relay Agent, converting the broadcast into a unicast frame addressed directly to the central DHCP server at 10.45.10.50.

Step-by-Step Solution

1
Identify the cause of DHCP request drops across subnets
Routers block broadcast frames (such as DHCPDISCOVER sent to 255.255.255.255) by default to prevent broadcast storms across network boundaries.
Layer 3 boundaries isolate broadcast domains.
2
Determine the required relay agent placement
The router interface receiving the client broadcast (subnet 10.45.80.0/24 default gateway) must act as a DHCP Relay Agent.
The relay agent intercept broadcast traffic on the client subnet and encapsulates it into unicast traffic directed to the central server IP address.
3
Select the correct interface configuration command
Applying the IP helper address command on the client-facing interface routes UDP broadcasts (including DHCP on port 67) to 10.45.10.50.
This enables cross-subnet IP addressing service delivery without placing a DHCP server on every local segment.

Key Concept

DHCP Relay / IP Helper Agent Configuration
Estimated Time:1m 15s
Rate this question

Topics

IP Addressing Services

More questions from this topic