When the switch is configured with the MFF function and a static gateway address, users with static IP addresses must send ARP request packets or gratuitous ARP packets to trigger creation of MFF user entries on the switch. Otherwise, the users cannot ping each other. When you use a tester to simulate users with static IP addresses, ensure that the tester can send ARP request packets and gratuitous ARP packets. If the tester cannot send ARP request packets or gratuitous ARP packets, the switch does not create MFF entries for the users with static IP addresses, and the users cannot ping each other.        

MFF Features

Static Gateway

The static gateway is applicable to the scenario where the IP addresses are set statically. When users are assigned IP addresses statically, the users cannot obtain the gateway information through the DHCP packets. In this case, a static gateway address needs to be configured for each VLAN. If the static gateway address is not configured, all the users cannot communicate with each other except for the DHCP users.

Gateway Address Detection and Maintenance

If the function of timed gateway address detection is enabled, MFF sends detection packets periodically to check whether the gateway address needs to be updated.

The detection packet is a forged ARP packet whose source IP address and MAC address are the addresses of the first user in the MFF user list. If the first user entry is deleted, the MFF selects another user entry to forge the ARP packet. If the gateway does not have any matching user information after the user entry is deleted, the MFF deletes the probe information.

ARP Proxy

The Layer 3 communication between users is implemented through the ARP proxy. The ARP proxy reduces the number of broadcast packets at the network side and user side.

The MFF processes ARP packets as follows:

• Responds to the ARP requests of users.

  The MFF substitutes for the gateway to respond to the ARP requests of users. Therefore, all the packets of users are forwarded at Layer 3 by the gateway. The ARP packet of a user may be the request for the gateway address or the request for the IP addresses of other users.

• Responds to the ARP requests of the gateway.

  The MFF substitutes for user hosts to respond to the ARP requests of the gateway. If the ARP entry mapping the request of the gateway exists on the MFF, the MFF returns a response with the requested address to the gateway. If the entry does not exist, the MFF forwards the request. In this way, the number of broadcast packets is reduced.

• Monitors the ARP packets on the network and updates the IP address and MAC address of the gateway.

Server Deployment on the Network

The IP address of the server can be the IP address of the DHCP server, the IP address of another server, or the virtual IP address of the VRRP group.

If a network interface receives an ARP request whose source IP address is the IP address of the server, the interface responds to the ARP request as a gateway. That is, the packets sent from users are forwarded to the gateway, and then sent to the server. The packets sent by the server, however, are not forwarded to the gateway.