When the packet's destination MAC-address is unknown for the switch (not included in its address table), the unit sends this packet to all hosts of the network, except for the sender interface.
This phenomenon is called "unicast-flood". The most common reasons of unicast-flood are:
- MAC address table overflow (a common problem in large networks);
- Hosts with ARP timers greater than the address cache timeout;
- Incorrect STP settings;
- Incorrect switch groups settings (in particular, when the switch groups for receiving and sending traffic are different).
InfiNet Wireless units provide unicast-flood protection. In this case, you can allow unlimited unicast-flood without protection filter by setting the check box in MAC Switch settings:
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R5000 unit sends packets with unknown MAC-address to all ports until it receives a response with the packet which contains this address as the sender. After this the unit will "learn" (i.e., the unit adds the MAC-address to its address table and reserves this MAC-address for the port where the packet was received). If the unit can't learn in 4 seconds, and packets still arrive, traffic to this direction will be blocked for 4 seconds. Then the process repeats.
This process has the following representation in the graphs, for example, in the unit statistics graphs:
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Also, unicast-flooding can be detected in the "Switch Statistics" section of the "Device Status" tab:
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R5000 units react to unidirectional traffic (which is not a unicast-flood) in a similar manner. This happens, for example, in case of generating "artificial" traffic (using specialized units or software) or when the real traffic is unidirectional. In these cases, it is recommended to allow unlimited unicast-flood without protection filter by checking the appropriate box in the settings (see above).