When you enable MAC pinning on an interface in a bridge domain or VPLS domain, MAC addresses learned over that interface cannot be relearned on any other interface in the same bridge domain or VPLS domain until the MAC address either ages out on the first interface or is cleared from the MAC table. If a packet with the same MAC address arrives at any other interface in the same bridge domain, it is discarded. This, effectively, controls MAC address moves and prevents the creation of loops in Layer 2 bridges and VPLS domains.
