Understanding Unknown Unicast Forwarding

 

Unknown unicast traffic consists of unicast packets with unknown destination MAC addresses. By default, the switch floods these unicast packets that traverse a VLAN to all interfaces that are members of that VLAN. Forwarding this type of traffic can create unnecessary traffic that leads to poor network performance or even a complete loss of network service. This flooding of packets is known as a traffic storm.

To prevent a traffic storm, you can disable the flooding of unknown unicast packets to all VLAN interfaces by configuring specific VLANs or all VLANs to forward all unknown unicast traffic traversing them to a specific interface. You can configure multiple VLANs to forward unknown unicast packets to the same interface or configure different interfaces for different VLANs. This channels the unknown unicast traffic traversing VLANs to specific interfaces instead of flooding all interfaces.