An enterprise network has deployed a centralized DHCP server on VLAN 100 (). Client workstations on VLAN 15 () and VLAN 25 () connect to a Layer 3 switch serving as their default gateway but fail to receive dynamic IP leases, resulting in APIPA address assignments. Which of the following configuration steps and operational mechanics must be implemented on the Layer 3 switch to resolve this issue? (Select TWO.)
- Configure the `ip helper-address 10.100.0.10` command directly under the Switched Virtual Interfaces (SVIs) for VLAN 15 and VLAN 25.Answer
- The switch converts incoming client DHCP broadcasts into unicast UDP packets destined for port 67 of the central server address.Answer
- CConfigure the `ip helper-address 10.100.0.10` command once in global configuration mode to apply across all defined switch subnets.
- DConfigure inter-VLAN Access Control Lists (ACLs) to permit TCP destination port 67 traffic from the client SVIs to the DHCP server.
Answer
The Layer 3 switch must be configured with `ip helper-address 10.100.0.10` on the SVIs for VLAN 15 and VLAN 25, and the switch operates by relaying broadcast DHCP client packets as unicast UDP destination port 67 traffic to the central server.
DHCP clients broadcast initial DHCPDISCOVER packets within their local VLAN. Because Layer 3 devices drop broadcasts, a DHCP Relay Agent (`ip helper-address`) must be configured on each client-facing Layer 3 interface (SVI). Upon receiving the broadcast, the relay agent converts the request into a unicast UDP packet (using UDP port 67 for both source and destination or forwarding to UDP 67) and sends it directly to the unicast IP address of the remote DHCP server.
Step-by-Step Solution
Key Concept
DHCP Relay Agent Architecture and UDP Forwarding Mechanics
Estimated Time:2m 0s