A network engineer is configuring a Cisco IOS router to relay DHCP requests from hosts on VLAN 50 () to a centralized DHCP server with the IP address located on VLAN 10. The default gateway for VLAN 50 is configured on subinterface GigabitEthernet 0/0/0.50.
Which two statements accurately describe the required configuration and behavior of the DHCP relay agent in this scenario? (Select TWO.)
- The `ip helper-address 10.10.10.5` command must be configured under subinterface GigabitEthernet 0/0/0.50.Answer
- The router converts incoming client DHCP DISCOVER broadcast packets into unicast UDP packets directed to 10.10.10.5.Answer
- CThe `ip helper-address 10.10.10.5` command must be configured on the router interface connected directly to the DHCP server subnet.
- DThe router floods incoming client DHCP DISCOVER packets out all active trunk ports as Layer 2 broadcast frames.
Answer
The helper address command must be applied on subinterface GigabitEthernet 0/0/0.50, and the router converts incoming client broadcast packets into unicast UDP packets directed to the DHCP server IP address.
DHCP relay agents must be configured on the client-facing gateway interface that receives client broadcast messages. When a client broadcasts a DHCP DISCOVER message, the router intercepts it on subinterface GigabitEthernet 0/0/0.50, populates the Gateway IP Address (giaddr) field with its own interface IP address, and unicasts the frame to the specified DHCP server IP address (10.10.10.5).
Step-by-Step Solution
Key Concept
DHCP Relay Agent Interface Binding and Broadcast-to-Unicast Forwarding Mechanics