MFF operation modes

The manual mode applies to a scenario where IP addresses are statically assigned to the hosts, and the hosts cannot obtain the gateway information through DHCP. A 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 with the host's MAC address to the gateway according to the ARP snooping entries. The MFF device also forges ARP requests to get the gateway's MAC address based on ARP snooping entries.

After learning the gateway's MAC address and then receiving an ARP packet with a different source MAC address from the default gateway, the MFF device updates the gateway's MAC address.

The automatic mode applies to a scenario where hosts use DHCP to obtain IP addresses.

In automatic mode, a DHCP snooping device resolves Option 3 in the received DHCP ACK message (Router IP option) to obtain a gateway for the client's 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.

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.

If the source MAC address of an incoming ARP packet from a gateway is different from that of the gateway, the MFF device updates the gateway's MAC address.