Allied Telesis AT-S112, AT-GS950/16PS manual Port Priority Value

Chapter 7: LACP Port Trunks

Port Priority Value

The switch uses a port’s LACP priority to determine which ports are active and which are in the standby mode in situations where the number of ports in the aggregate trunk exceeds the highest allowed number of active ports. This parameter is a value in a range of 1 to 255, based on the port number. For instance, the priority values for ports 2 and 11 are 002 and 011, respectively. The lower the number, the higher the priority. Ports with the highest priorities are designated as the active ports in an aggregate trunk.

For example, if both 802.3ad-compliant devices support up to six active ports and there are a total of eight ports in the trunk, the six ports with the highest priorities (lowest priority values) are designated as the active ports, and the others are placed in the standby mode. If an active link goes down on a active port, the standby port with the next highest priority is automatically activated to take its place.

The selection of the active links in an aggregate trunk is dynamic and changes as links are added, removed, lost, or reestablished. For example, if an active port loses its link and is replaced by another port in the standby mode, the re-establishment of the link on the originally active port causes the port to return to the active state by virtue of having a higher priority value than the replacement port, which returns to the standby mode.

Two conditions must be met for a port in an aggregate trunk to function in the standby mode. First, the number of ports in the trunk must exceed the highest allowed number of active ports and, second, the port must be receiving LACPDU packets from the other device. A port functioning in the standby mode does not forward network traffic. However, it continues to send LACPDU packets. If a port that is part of an aggregator does not receive LACPDU packets, it functions as a normal Ethernet port and forwards network packets along with LACPDU packets.

Note

You can adjust the value of a port’s priority.

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