What is Frame Flooding?

Frame Flooding is a procedure followed by a switch in which the switch forwards the Ethernet frame received by it to all the ports except the incoming port. Although the process seems identical to another procedure known as an Ethernet Broadcast, it is different in origin from a broadcast.

• Ethernet Frame: 

Source Address	Destination Address
12.EF.56.98.FF	FF.FF.FF.FF.FF

• MAC Address Table:

Port Number	MAC Address
00	12.EF.56.98.FF
01	AB.CD.EF.12.34.56
02	BC.DE.AB.56.32.14

In an Ethernet Broadcast, the Ethernet frame is addressed to the broadcast MAC address, i.e., FF:FF:FF:FF:FF:FF. This makes the frame a Broadcast Frame. This value of the MAC address instructs the switch to send the Ethernet frame to all the active ports except the incoming port. The switch does not look into the MAC Address Table for this MAC Address. Protocols like ARP depend on Ethernet broadcasts.

• Ethernet Frame: 

Source Address	Destination Address
12.3E.EF.65.11.FF	FF.12.34.44.AB

• MAC Address Table:

Port Number	MAC Address
00	12.EF.56.98.FF
01	AB.CD.EF.12.34.56
02	BC.DE.AB.56.32.14

In Frame Flooding, when the switch receives an Ethernet frame with a destination address other than the broadcast address, it looks for an entry against the destination MAC address stored in the frame. If there is no entry found in the MAC Address Table, the frame is forwarded to all the active ports except the incoming port. This ensures that the data frame reaches the intended destination, even if the MAC Address is not mapped to the port number in the MAC Address Table. This leads to a similar effect as an Ethernet Broadcast.

Ethernet Broadcast Vs Frame Flooding:

Ethernet Broadcast	Frame Flooding
The destination MAC Address must be the Ethernet Broadcast Address i.e. FF:FF:FF:FF:FF:FF.	The destination MAC Address may be anything other than the Ethernet Broadcast Address.
The Switch does not check MAC Address Table for any entry.	The switch checks the MAC Address Table and executes Frame Flooding if the Destination MAC Address is not in the table.
Protocols like ARP depend on Ethernet Broadcast.	No protocols depend on Frame Flooding.

In Frame Flooding, the switch sends the packets on all ports when it doesn’t know the port number on which to forward the data frame.