System Priority; Port Priority Value - Allied Telesis AT-GS950/24 User Manual

System Priority

Port Priority Value

It is possible for two devices interconnected by an aggregate trunk to
encounter a conflict when they form the trunk. For example, the two
devices might not support the same number of active ports in an
aggregate trunk or might not agree on which ports are active and which
are in standby mode.
If a conflict does occur, the two devices need a mechanism for resolving
the problem and deciding whose LACP settings take precedence. This is
the function of the system LACP priority value. This value is used
whenever the devices encounter a conflict creating a trunk - the lower the
number, the higher the priority. As a result, the settings on the device with
the higher priority take precedence over the settings on the other device. If
both devices have the same system LACP priority value, the settings on
the switch with the lowest MAC address take precedence. In the AT-S109
Version 1.1.0 Management software, the MAC address is called the
System ID.
The LACP System Priority is pre-assigned and you cannot alter this
parameter.
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.
AT-GS950/24 Web Interface User Guide
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