MFF operation modes

The manual mode applies to networks where the hosts' IP addresses are manually configured. The hosts cannot obtain the gateway information through DHCP. VLAN maintains only the MAC address of the default gateway.

After receiving an ARP request for a host's MAC address from the gateway, the MFF device directly replies the host's MAC address to the gateway according to the ARP snooping entries. After learning the gateway's MAC address, the MFF device updates the MAC address upon receiving an ARP packet with a different sender MAC address from the default gateway.

The automatic mode applies to networks that allocate IP addresses to hosts through DHCP.

In automatic mode, the device configured with DHCP snooping resolves Option 3 (Router IP option) in the received DHCP ACK message to obtain a gateway for the DHCP snooping entry. If the DHCP ACK message contains multiple gateway addresses, only the first one is recorded for the entry. If the message contains no gateway IP address, the first gateway recorded by the current VLAN is used.

If the sender MAC address of an ARP packet from a gateway is different from the MAC address recorded for the gateway, the MFF device updates the gateway's MAC address.

	NOTE: In MFF automatic mode, a VLAN can learn and maintain a maximum of 20 gateways. The gateway IP addresses will not be updated, and the gateway information does not age out unless MFF is disabled.