Learning and unlearning in a network switch

摘要

A modified Ethernet packet includes a MAC address unlearn flag. A port receiving the packet unlearns the specified MAC address, i.e., removes the corresponding entry from its forwarding table. Unlearn packets may be generated by a switch CPU in response to detection of a port failure in order to remove entries associated with the failed port. The modified Ethernet packet may alternatively, or also, include an attribute learn field. An Ethernet switch is operable to learn the specified attribute in response to receipt of the packet. Attributes that may be specified include: copy-to-CPU; static; class-of-service; source-discard; destination-discard; and L3. The copy-to-CPU attribute is operable to prompt copying of subsequent packets observed with the same SA to the CPU. The static attribute is operable to prompt prevention of a specified MAC address from being removed from a forwarding table due to aging. The class-of-service attribute is operable to prompt override of a packet class-of-service value with a specified value for subsequent packets of a specified MAC address. The source-discard attribute is operable to prompt discard of subsequent packets having a specified SA. The destination-discard attribute is operable to prompt discard of subsequent packets having a specified DA. The L3 attribute is operable to prompt packets destined for a specified MAC address to be routed rather than switched.