Allied Telesis AT-S63 - Manual (Page 88)

Chapter 6: LACP Port Trunks
88 Section I: Basic Operations
LACP System Priority
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 to be active and
which are to be in standby.
If a conflict does occur, the two devices need a mechanism for resolving
the problem and deciding whose LACP settings are to take precedence.
This is the function of the system LACP priority value. A hexadecimal
value of from 1 to FFFF, this parameter is used whenever the devices
encounter a conflict creating a trunk. The lower the number, the higher the
priority. 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.
This parameter can prove useful when connecting an aggregate trunk
between the AT-9400 Switch and another 802.3ad-compliant device that
does not have the same LACP trunking capabilities. If the other device’s
capability is less than that of the AT-9400 Switch, you should give that
device the higher priority so its settings are used by both devices when
forming the trunk.
For example, an aggregate trunk of six links between an AT-9400 Switch
and an 802.3ad-compliant device that supported up to four active links at
one time could possibly result in a conflict. The AT-9400 Switch would try
to use all six links as active, because it can handle up to eight active links
in a trunk at one time, while the other device would want to use only four
ports as active. By giving the other 802.3ad device the higher priority, the
conflict is avoided because the AT-9400 Switch would use only four active
links, as directed by the other 802.3ad-compliant device. The other ports
would remain in the standby mode.