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Cisco Wireless LAN Controller Configuration Guide
OL-8335-02
Chapter 3 Configuring Ports and Interfaces
Enabling Link Aggregation
Step 10 After you configure STP settings for the ports, enter config spanningtree switch mode enable to enable
STP for the controller. The controller automatically detects logical network loops, places redundant
ports on standby, and builds a network with the most efficient pathways.
Step 11 Enter show spanningtree port and show spanningtree switch to verify that your changes have been
saved.
Enabling Link Aggregation
Link aggregation (LAG) is a partial implementation of the 802.3ad port aggregation standard. It bundles
all of the controller’s distribution system ports into a single 802.3ad port channel, thereby reducing the
number of IP addresses needed to configure the ports on your controller. When LAG is enabled, the system
dynamically manages port redundancy and load balances access points transparently to the user.
Cisco 4400 series controllers support LAG in software release 3.2 and higher, and LAG is enabled
automatically on the Cisco WiSM controllers. Without LAG, each distribution system port on the
controller supports up to 48 access points. With LAG enabled, a 4402 controller’s logical port supports
up to 50 access points, a 4404 controller’s logical port supports up to 100 access points, and the logical
port on each Cisco WiSM controller supports up to 150 access points.
Figure 3-11 illustrates LAG.
Figure 3-11 Link Aggregation
LAG simplifies controller configuration because you no longer need to configure primary and secondary
ports for each interface. If any of the controller ports fail, traffic is automatically migrated to one of the
other ports. As long as at least one controller port is functioning, the system continues to operate, access
points remain connected to the network, and wireless clients continue to send and receive data.