Campus lan and Wireless lan solution Design Guide

WLAN controller link aggregation 
Cisco wireless controller appliances have multiple physical Ethernet ports. In typical deployments, one or more 
WLANs/service set identifiers (SSIDs) are mapped to a VLAN interface, which is then mapped to a physical port.
In a centralized design, wireless traffic is backhauled across the network infrastructure and terminated on the 
physical ports. With the use of a single physical port per WLAN, the throughput of each WLAN is limited to the 
throughput of the port. Therefore, an alternative is to deploy link aggregation (LAG) across the distribution 
system ports, bundling them into a single high speed interface.
When LAG is enabled, the wireless controller dynamically manages port redundancy and load-balances APs 
transparently. If any of the controller ports fail, traffic is automatically migrated to one of the other ports. If at 
least one controller port is functioning, the wireless controller continues to operate, APs remain connected to 
the network, and wireless clients continue to send and receive data.
Preferred redundancy – Cisco Catalyst 9800 HA SSO pair connected to redundant single logical switch 
LAG requires an EtherChannel Port Group to be configured on the attached Cisco Catalyst switch. The 
EtherChannel port group can be configured across multiple linecards on the switch, or across switches in a 
Cisco StackWise Virtual configuration, for additional redundancy. When configured across switches the group is 
referred to as a Multichassis EtherChannel (MEC). The EtherChannel is configured using 802.1Q trunk 
encapsulation to carry multiple VLANs from the controllers into the switching domain.
The following figure shows an example of wireless controller link aggregation in a high availability configuration 
to a Cisco StackWise Virtual pair. Similar connectivity is used when connecting to a distribution switch stack.