Allied Telesis AT-8700XL, RAPIER I, X900-48FE, AT-8900 Limiting Rapid MAC Movement, PortDisable

Software Version 2.8.1 27

Limiting Rapid MAC Movement

This Software Version introduces the ability to limit rapid MAC movement. MAC address thrashing occurs when MAC addresses move rapidly between one or more ports or trunks. For example, certain MAC addresses are learnt on one port, then very shortly afterwards are learnt on another port, then learnt on the original port again, and so on. This typically occurs when there is an uncontrolled loop on the network.

Disabling a port There are different ways you can disable a port when thrashing is detected. These are called thrash actions:

■learnDisable

Address learning is temporarily disabled on the port.

■portDisable

The port is logically disabled. Traffic flow is prevented, but the link remains up. The device at the other end does not notice that the port has changed status, and the link LEDs at both ends stay on. This is equivalent to entering the disable switch port command.

■linkDown

The port is physically disabled and the link is down. This is equivalent to entering the disable switch port link=disabled command.

■vlanDisable

The port is disabled only for the VLAN on which thrashing has occurred. It can still receive and transmit traffic for any other VLANs of which it is a member.

When a MAC address is thrashing between two ports, only one of those ports is disabled. When multiple ports are involved, enough ports are disabled to prevent the storm.

To set a thrash action for a port, use the command:

set switch port={port-listall} [thrashaction={learndisablelinkdownnoneportdisablevla ndisable}]

To view the thrash action that is set for a port, use the command:

show switch port={port-listall}

To set a thrash action for a trunk, use one of the commands:

create switch trunk=trunk [port=port-list] [thrashaction={learndisablelinkdownnoneportdisablevla ndisable}]

set switch thrashlimit=trunk [thrashaction={learndisablelinkdownnoneportdisablevla ndisable}]

To view the thrash action that is set for a trunk, use the command:

show switch trunk={trunk}

Software Version 2.8.1 C613-10477-00 REV B