With DHCP Smart Relay functionality, the relay agent inserts both the primary and secondary IP addresses of the client-facing interface (VLAN or VRRP) as the gateway IP address in the DHCP packet. The DHCP relay agent can use secondary IP addresses if there is no reply to the DHCPOFFER message on the server.
For more information about secondary IP addresses, see Secondary IP Interfaces.
DCHP Smart Relay functionality provides two modes:
parallel
In parallel mode, the relay agent makes multiple copies of DHCP requests and inserts each IP address of the client-facing interface (VLAN or VRRP) as the gateway address in each copy of the request. The switch simultaneously relays multiple packets to the DHCP server, assigning each packet the correct IP address in the correct subnet.
sequential
In sequential mode, the relay agent forwards received DHCP packets from all IP addresses on the VLAN or VRRP interface one at a time, starting with the primary address and continuing with each secondary address. Each time a packet is received, the agent selects an address on the VLAN or VRRP interface. The relay agent forwards three client requests to the DHCP Server before repeating the process and cycling through the primary and all secondary IP addresses.
For DHCP Smart Relay to use a subset of VRRP addresses, you must configure the agent IP in the forwarding path with a VRRP address and you must configure at least the following VRRP items on the VLAN:
Note
These requirements are not specific to DHCP Smart Relay and also apply to DHCP Relay in general.VRRP version
VRRP address
VRRP status (enabled)
For configuration information, see the following sections: