A client workstation on VLAN 20 () broadcasts a DHCPDISCOVER message to obtain an IP configuration. The Layer 3 switch interface acting as the default gateway for VLAN 20 is configured with an IP helper address pointing to a centralized DHCP server at on VLAN 99. Which of the following operations accurately describe how the relay agent processes and forwards this message? (Select TWO.)
- The relay agent inserts the IP address of the VLAN 20 interface into the Gateway IP Address (giaddr) header field.Answer
- The relay agent converts the client broadcast frame into a unicast IP packet targeted to using UDP port 67.Answer
- CThe relay agent forwards the message as a Layer 2 broadcast frame across all trunk links using TCP port 67.
- DThe relay agent populates the Gateway IP Address (giaddr) header field with the IP address of the destination DHCP server ().
Answer
The relay agent populates the Gateway IP Address (giaddr) field with the IP address of its local receiving interface (VLAN 20 gateway) and encapsulates the client's broadcast into a unicast IP packet directed to the destination DHCP server using UDP port 67.
When a Layer 3 relay agent intercepts a broadcast DHCPDISCOVER message, it rewrites the packet payload by setting the Gateway IP Address (giaddr) field to its local client-facing interface address. It then converts the Layer 2 broadcast into a unicast IPv4 datagram and forwards it directly to the IP address specified in the helper configuration using UDP destination port 67.
Step-by-Step Solution
Key Concept
DHCP Relay Agent Operational Mechanics and Packet Header Modification