Configuration manual

Link Aggregation Overview
Fixed Switch Configuration Guide 11-3
• Attaches the port to the aggregator used by the LAG, and detaches the port from the
aggregator when it is no longer used by the LAG.
• Uses information from the partner device’s link aggregation control entity to decide whether
to aggregate ports.
The operation of LACP involves the following activities:
• Checking that candidate links can actually be aggregated.
• Controlling the addition of a link to a LAG and the creation of the group if necessary.
• Monitoring the status of aggregated links to ensure that the aggregation is still valid.
• Removing a link from a LAG if its membership is no longer valid, and removing the group if it
no longer has any member links.
Multi-port LAGs will continue to operate as long as there is at least one active port in the LAG.
Therefore, there is no need to create backup single port LAGs or to specifically assign the LAG and
all its physical ports to the egress list of the LAG’s VLAN.
How a LAG Forms
LAGs form automatically with LACP enabled on the device. There are four criteria for forming a
LAG. Both actor and partner ports must:
1. Operate in full duplex mode.
2. Have matching local LAG and physical port admin keys for the device controlling LAG
formation.
3. Operate in parallel in that a LAG can have only two devices associated with it.
4. Consist of two or more physical actor to partner port pairings unless the single port LAG
feature is enabled.
Figure 11-1 on page 11-4 displays a LAG formation example containing three devices with five
100Mbps ports and three 1Gb ports configured. For this example, all ports are operating in full-
duplex mode, and the admin key for all LAG ports has been set to 100. Device A is the actor and
therefore determines which ports will join a LAG. Devices B and C are the partners.
In our example two LAGs have formed because the actor ports are shared between two partner
devices. Attempting to form a single LAG using all the actor ports would have broken the rule
that actor and partner ports must operate in parallel.
Note: A given link is allocated to, at most, one LAG at a time. The allocation mechanism attempts to
maximize aggregation, subject to management controls.