Link Aggregation Control Protocol (LACP) is a part of an IEEE specification (802.3ad) that allows you to bundle several physical ports together to form a single logical channel. LACP allows a switch to negotiate an automatic bundle by sending LACP packets to a peer. By using the LACP, the wireless controller learns the identity of peers that are capable of supporting LACP, and the capabilities of each port. The LACP then dynamically groups similarly configured ports into a single logical link (channel or aggregate port). Similarly, configured ports are grouped based on hardware, administrative, and port parameter constraints. 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.

Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that you can run on controllers. PAgP facilitates the automatic creation of EtherChannels by exchanging PAgP packets between Ethernet ports. PAgP packets are sent between Fast EtherChannel-capable ports in order to form a channel. When any of the active ports fail, a standby port becomes active.

By using PAgP, the controller learns the identity of partners that are capable of supporting PAgP and the capabilities of each port. PAgP then dynamically groups similarly configured ports (on a single device in a stack) into a single logical link (channel or aggregate port). Similarly, configured ports are grouped based on hardware, administrative, and port parameter constraints.

From Cisco IOS XE Bengaluru 17.5.1 onwards, the flexibility to number the port channel interface numbers between 1 and 64 is supported on the following Cisco Catalyst 9800 Series Wireless Controllers:

• Cisco Catalyst 9800-CL Wireless Controller for Cloud: The available range on the CLI is 1 to 64. The maximum supported port channel interfaces are 64.

• Cisco Catalyst 9800-L Wireless Controller: The available range on the CLI is 1 to 64. The maximum supported port channel interfaces are 14.

• Cisco Catalyst 9800-40 Wireless Controller: The available range on the CLI is 1 to 64. The maximum supported port channel interfaces are 16.

• Cisco Catalyst 9800-80 Wireless Controller: The available range on the CLI is 1 to 64. The maximum supported port channel interfaces are 64.

For example on the Cisco Catalyst 9800-L Wireless Controller, port-channel interface numbers can be anywhere between 1 and 64, as long as the total number of port-channel interfaces are 14 or lesser.

Note

If you have configured 16 port-channel interfaces on the Cisco Catalyst 9800-40 Wireless Controller, and if the configured port-channel interfaces have reached their limitation, the following error message is displayed when you try to configure the 17th port-channel interface: Device(config)# Dec 15 08:58:22.209 CST: %ETC-5-CANNOT_ALLOCATE_AGGREGATOR: Aggregator limit reached, cannot allocate aggregator for group 17 When you downgrade from Cisco IOS XE Bengaluru 17.5.1 to an earlier version, and if the port channels are configured with a higher range than the supported range in the earlier version, the following errors are displayed when the earlier version is started. The non supported port channels disappear after the downgrade is completed. interface Port-channel29 ^% Invalid input detected at '^' marker. interface Port-channel35 ^% Invalid input detected at '^' marker. Note that the HA pairing remains intact after downgrade.

Flow control enables connected Ethernet ports to control traffic rates during congestion by allowing congested nodes to pause link operation at the other end. If one port experiences congestion and cannot receive more traffic, it notifies the other port by sending a pause frame to stop sending until the condition clears. Upon receipt of a pause frame, the sending device stops sending any data packets, preventing any data packet loss during the congestion period.

Flow control is enabled by default for both bay0 and bay1 ports as a day-1 behavior. We suggest turning on flow control on uplink switch if overruns are seen on a Cisco Catalyst 9800-L Wireless Controller due to burst traffic. This will help uplink switch to honor flow control settings enabled on the controller.

Note	Though the show command might show the status as flow control off or unsupported on the controller's CLI, the actual & default behavior is turned on. For more information, check https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwk52366.

To configure LAG in ON mode, multiple port-channel interfaces must be created, and these interfaces should be added to the corresponding port bundle. LACP should also be configured on the uplink switch for the LACP bundle to come up.

From Cisco IOS XE Amsterdam 17.2.1, Multichassis Link Aggregation Group (multi-LAG), which provides flexibility in connecting the controller to a switch's infrastructure is supported. Using multi-LAG, you can connect the multiple uplinks from the controller to the separated uplink switches. The controller supports VLAN-based traffic splitting when connected to a multiswitch topology. This provides the ability to distribute traffic on different uplinks, based on VLANs, for example, supporting a use case where guest traffic can be completely isolated to a different switch or network from the enterprise network. Same VLAN cannot be configured on both the uplinks.

You can connect a LAG to a single switch. However, different VLANs must be connected to different LAGs. The redundancy port must be connected to the same distribution switch as the uplinks, or back to back.

Multi-LAG is supported in LAG ON mode, LACP, and PAgP modes.

• Each LAG must be connected to a single switch.

• Different VLANs must be assigned to different LAGs.

• If the primary LAG fails, automatic failover to secondary LAG is not supported.

• The interface on the controller does not come up when you shut or unshut the port on the switch port.

  Note	This is specific to Cisco Catalyst 9800-CL Cloud Wireless Controller in KVM environment for SR-IOV.

The Cisco Catalyst 9800-80 Wireless Controller has eight ports, while the Cisco Catalyst 9800-40 and Cisco Catalyst 9800-L wireless controllers have four ports each. You can create multi-LAGs of ports with similar capabilities, for example, 2.5 G and 2.5 G, or 10 G and 10 G. You cannot have a 2.5 G and a 10 G port in a port channel group with a minimum of two ports in one LAG.