An enterprise campus utilizes a Layer 3 core switch handling routing for multiple virtual LANs. Host devices on VLAN 50 () fail to acquire dynamic IP address assignments upon boot, resulting in self-assigned APIPA addresses (). Packet analysis on the core switch reveals that incoming broadcast messages arrive at the VLAN 50 interface, but the switch fails to encapsulate and forward these requests as unicast traffic to the remote DHCP server located at . Which configuration issue on the core switch is preventing clients on VLAN 50 from receiving DHCP leases?
- The ip helper-address statement is omitted from the Switch Virtual Interface (SVI) for VLAN 50.Cevap
- BThe ip helper-address statement was configured on the physical uplink port connecting to the DHCP server rather than the client gateway SVI.
- CThe core switch is improperly attempting to establish a TCP three-way handshake with the DHCP server prior to relaying lease requests.
- DThe relay agent is forwarding client discovery packets using target UDP port 68 instead of target UDP port 67.
Cevap
The ip helper-address statement is omitted from the Switch Virtual Interface (SVI) for VLAN 50.
For a Layer 3 switch or router to act as a DHCP relay agent, the relay directive (such as `ip helper-address`) must be applied to the specific Layer 3 ingress interface (SVI or physical interface) that receives the client's broadcast traffic. When clients on VLAN 50 broadcast a DHCPDISCOVER message, the core switch checks SVI 50 for a helper address. If missing, the broadcast is discarded at the Layer 3 boundary. When properly configured on SVI 50, the switch converts the broadcast into a unicast UDP packet (destined for port 67 on the DHCP server) and populates the `giaddr` field with SVI 50's IP address.
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Anahtar Kavram
DHCP Relay Agent Placement and Gateway SVI Configuration