A network technician is configuring an enterprise router to forward client DHCP requests from a newly created VLAN to a centralized DHCP server situated on a remote management subnet. Clients on the new VLAN are currently receiving APIPA addresses because Layer 3 routers block broadcast traffic by default. Which configuration action on the router interface serving the new VLAN will successfully enable host IP addressing from the central server?
- Configure an IP Helper address on the VLAN interface to relay DHCP broadcast frames as unicast UDP packets to the remote server IP address.Answer
- BAdd a CNAME record on the local router pointing the VLAN gateway hostname directly to the DHCP server's fully qualified domain name.
- CCreate an ACL rule on the interface allowing incoming client broadcast traffic over TCP port 67 to traverse the router WAN links.
- DConfigure a secondary static IP scope directly on the DHCP server without modifying the intervening router interface.
Answer
Configuring an IP Helper address on the VLAN interface to relay DHCP broadcast frames as unicast UDP packets to the remote server IP address.
DHCP clients initiate address acquisition using local broadcast messages (DHCPDISCOVER). Because routers do not forward broadcast packets between subnets, a DHCP relay agent (configured via an IP helper command on the router's local VLAN interface) must intercept these broadcasts and forward them as unicast UDP traffic to the centralized DHCP server.
Step-by-Step Solution
Key Concept
DHCP Relay Agent / IP Helper Operations