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Link Aggregation Screen (802.3ad Main Menu Screen)
Port Configuration Menu Screens 6-25
According to the IEEE 802.3ad standard, a port does not detach from an aggregator because of link
loss. If a port is attached to an aggregator and the link is removed, the port’s mux machine will
transition from COLLECTING to ATTACHED; however, it will remain attached to the same
aggregator.
Ports that are attached to an aggregator will enter a Spanning Tree state of AGGREGATING on the
Spanning Tree screens, just as they do when manually placed in a trunk.
In this implementation, the concept of an aggregator is for a non-aggregated port to attach to,
although this aggregator doesn’t exist in any real sense. A port that is not a member of an
aggregation will be displayed in LM as attached to a non-existent aggregation. If a port instance
matches the aggregator instance it is attached to, that means it is not aggregating.
There are a few cases in which the 802.3ad implementation will disable a port’s ability to
aggregate by clearing the aggregable bit ActorOperState:
• A port is attached to another port on this same switch (loopback). There is no available
aggregator for 2 or more ports with the same LAGID. This can happen if either there are simply
no available aggregators, or if none of the aggregators have a matching operational key and
system priority.
• A port is in the same LAG as another port but is running at a slower speed. Ports running at
different speeds are not allowed to aggregate according to 802.3ad.
There is a maximum of six aggregators per module.
Definitions to Know
Rapid Reconfiguration Spanning Tree
Rapid Reconfiguration is an enhancement to the legacy 802.1D Spanning Tree implementation,
which implements a rapidly converging Spanning Tree algorithm that is event-driven instead of
timer-driven.
Spanning Tree
When multiple links are connected from one switch to another, it is necessary that only one link be
allowed to switch network traffic. Due to the functionality of a switch, if multiple links were
active, a packet would end up “looping” around in those links indefinitely. This problem is well
documented and is the reason that bridges implement the Spanning Tree Protocol (STP).
NOTE: Ports running at half-duplex cannot aggregate.