Unknown Unicast flooding vs broadcast frame

[Chhayheng Chheang]

Hi Guys,

I read some articles the different between Unicast and Broadcast.
Let me explain what I understand from that, then please correct me if I am wrong.

When Source Frame Host-A tries sending Frame to Destination Frame Host-B. SWITCH will looking MAC-ADDRESS has in CAM Table or not, if not, it will flood (Broadcast) to all Destination port except the sender. 

After aged out in SWITCH is expired, the record MAC-ADDRESS of Hosts will delete from Tables, but Host-A still has MAC-ADDRESS of Host-B. It still back to do Broadcast again. I don't which situation Unknown Unicast Flooding occur.


Best Regards,
Chhayheng

[Reza Sharifi]

Hi,

Have a look at this discussion.

https://supportforums.cisco.com/discussion/10793141/flooding-vs-broadcast

HTH

[Georg Pauwen]

Hello Chhayeng,

what you describe is actually exactly what unicast flooding is:

The CAM table is used to direct traffic to specific ports based on the VLAN number and the destination MAC address of the frame. When there is no entry corresponding to the frame's destination MAC address in the incoming VLAN, the (unicast) frame will be sent to all forwarding ports within the respective VLAN, which causes flooding, otherwise known as unicast flooding.

A broadcast frame does not check the CAM table, it is basically simply a method deployed by a sender to deliver a packet to all possible recipients, by using a broadcast address. 

Check the link below for a better explanation of the difference:

Difference Between Flooding and Broadcasting

http://www.differencebetween.com/difference-between-flooding-and-vs-broadcasting/