Examkin

Question

Difficulty: MediumDHCP Server, Client, and Relay Agent Operation and Configuration

An enterprise network administrator is configuring a Cisco IOS router to forward DHCP requests from host clients in VLAN 30 (192.168.30.0/24192.168.30.0/24) to a centralized DHCP server located in VLAN 10 at IP address 10.10.10.5010.10.10.50. Host workstations in VLAN 30 connect to the router via subinterface `GigabitEthernet0/0.30`, and the DHCP server resides behind egress interface `GigabitEthernet0/1`. Which command must be configured under subinterface `GigabitEthernet0/0.30` on the router to enable DHCP relay services for the VLAN 30 workstations?

  1. ip helper-address 10.10.10.50Answer
  2. B
    ip helper-address 192.168.30.1
  3. C
    ip dhcp relay 10.10.10.50
  4. D
    ip helper-address 255.255.255.255

Answer

The command `ip helper-address 10.10.10.50` must be configured under the client-facing subinterface `GigabitEthernet0/0.30`.
Configuring `ip helper-address 10.10.10.50` under the client-facing subinterface (`GigabitEthernet0/0.30`) allows the router to intercept Layer 2 broadcast DHCP DISCOVER packets from host devices in VLAN 30. The router populates the `giaddr` (gateway IP address) field with `192.168.30.1` and converts the broadcast packet into a unicast IPv4 packet targeted directly to the central DHCP server at `10.10.10.50`.

Step-by-Step Solution

1
Identify the ingress client interface
The workstations in VLAN 30 send broadcast DHCP packets that hit the router subinterface `GigabitEthernet0/0.30`.
DHCP Relay Agents must be enabled on the specific gateway interface where broadcast client packets originate.
2
Determine the destination IP address for the relay command
The destination address must point to the remote DHCP server IP address (10.10.10.5010.10.10.50).
The relay agent converts client UDP broadcasts into unicast UDP packets directed towards the DHCP server's address.
3
Select the correct Cisco IOS syntax
The correct command syntax configured under the interface mode is `ip helper-address 10.10.10.50`.
Cisco IOS uses `ip helper-address [target-IP]` to relay UDP broadcast services including DHCP (UDP ports 67 and 68).

Key Concept

DHCP Relay Agent Configuration (`ip helper-address`)
Rate this question

Topics

DHCP Server, Client, and Relay Agent Operation and Configuration

More questions from this topic