Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 Bulletins

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Link aggregation is also used on the Cisco Catalyst 6500 Series WiSM. The WiSM consists of two Cisco 4404 Wireless LAN Controller

subsystems; the four gigabit links for each of the 4404 subsystems are aggregated, as shown in the Figure 9.

Figure 9. Link Aggregation on the Cisco WiSM

Note that link aggregation is enabled by default on the Cisco WiSM and cannot be disabled.

Notes on Link Aggregation

•

Any change to the link aggregation configuration will require the system to be rebooted.

•

When link aggregation is enabled, existing interfaces are modified as follows:

–

The management interface is moved to the link aggregation port.

–

The static AP-Manager interface is moved to the link aggregation port. All dynamic AP-Manager interfaces are removed from the system.

–

All VLAN-tagged dynamic interfaces are moved to the link aggregation port. Any untagged interfaces are removed from the system.

•

When link aggregation is disabled, existing interfaces are modified as follows:

–

The management interface is moved to Port 1

–

The static AP-Manager interface is moved to Port 1

–

All dynamic interfaces are moved to Port 1

•

The mechanism used to load-balance traffic across the links is determined by the Ethernet switch the controller connects to. The controller simply

sends a packet out on the same port that it received the packet on. For example, if an LWAPP packet from an access point enters the controller on
physical Port 1, the controller will remove the LWAPP wrapper, process the packet, and forward it back to the network on physical Port 1.

•

Link aggregation is enabled by default on the Cisco WiSM and cannot be disabled.

Benefits of Link Aggregation

•

Link Redundancy—Any single link in the bundle can go down and traffic will automatically migrate to the other links. As long as at least one of

the physical links is functioning, the system remains functional; access points remain connected to the switch and data service for users continues
uninterrupted.

•

Eliminates the Complexity of Configuring Primary and Backup Ports for the Management and Dynamic Interfaces—Link failure

protection is an inherent part of the link aggregation bundle and does not need to be configured by the network manager.

•

Simplified Configuration—Eliminates the need for multiple AP-Manager interfaces; only a single AP-Manager interface needs to be defined for

the system.

•

Simplified Network Design—No traffic engineering is needed to ensure distribution of traffic across the multiple physical interfaces; the

aggregate bandwidth of the link aggregation bundle is available to all logical interfaces on the controller.