A link aggregation group is a port-channeling technology that

• combines all of a controller’s distribution system ports into a single 802.3ad port channel

• reduces the number of IP addresses required for port configuration, and

• dynamically manages port redundancy and load-balances AP transparently to the corresponding user.

LAG simplifies controller configuration by eliminating the need to configure ports for each interface. If any controller port fails, traffic migrates automatically to other functioning ports. As long as at least one controller port is functioning, the system continues to operate. Wireless clients can continue to send and receive data, and APs remain connected to the network.

The wireless management VLAN can be assigned to only one port channel.

LACP is supported on a standalone controller from the Cisco IOS XE Gibraltar 16.12.x release. LACP is supported on an SSO pair from Cisco IOS XE Amsterdam 17.1.1s and later.

If a dual MAC entry is generated in the switchport MAC table when using ISE licensing enforcement, it may consume two licenses for a single AP. To avoid this issue when only one port is used, choose wired0.

A link aggregation control protocol (LACP) is a network protocol that:

• Bundles several physical ports together to form a single logical channel.

• Negotiates automatic bundling by sending LACP packets to a peer.

• Maintains network operation by dynamically grouping and rerouting traffic into a single logical link (channel or aggregate port) if any ports fail.

Link Aggregation Control Protocol (LACP) is a part of the IEEE 802.3ad specification. If any port in the bundle fails, traffic shifts to the remaining working ports, ensuring uninterrupted connectivity. APs and wireless clients can continue to send and receive data.

A port aggregation protocol is a Cisco-proprietary network protocol that facilitates the automatic combination 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 support 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.

A port channel interface number is a configuration identifier that uniquely distinguishes a port channel logical interface. It defines allowable ranges and limits depending on the controller model.

From Cisco IOS XE Bengaluru 17.5.1 onwards, port channel interface numbers from one to 64 are supported, with model-dependent limits on the following Cisco Catalyst 9800 Series Wireless Controllers:

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

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

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

• Cisco Catalyst 9800-80 Wireless Controller: The available range on the CLI is one 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 one and 64, provided that no more than 14 port-channel interfaces are configured.

Device(config)#
                Dec 15 08:58:22.209 CST: %ETC-5-CANNOT_ALLOCATE_AGGREGATOR: Aggregator limit reached, cannot allocate aggregator for group 17
            

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.

A flow control mechanism is a network protocol feature that:

• Enables connected Ethernet ports to control traffic rates during congestion by allowing congested nodes to pause link operation at the other end.

• Uses pause frames for signaling congestion and allows congested nodes to pause traffic from other nodes to prevent packet loss.

Flow control is enabled by default for both bay0 and bay1 ports as a first-day behavior. If you see overruns on a Cisco Catalyst 9800-L Wireless Controller due to burst traffic, enable flow control on the uplink switch. This change helps the uplink switch honor the flow control settings enabled on the controller.

Although the show command might indicate that flow control is off or unsupported in the controller’s CLI, the actual default behavior is that flow control is enabled. For more information, check https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwk52366.

A multichassis link aggregation group (multi-LAG) is a switch interconnection technology that:

• Connects multiple controller uplinks to separate uplink switches for redundancy and load balancing.

• Supports VLAN-based traffic splitting when connected to a multiswitch topology.

• Provides the ability to distribute traffic on different uplinks, based on VLANs. For example, guest traffic can be completely isolated to a different switch or network from the enterprise network. You cannot configure the same VLAN on both uplinks.

Starting with Cisco IOS XE Amsterdam 17.2.1, the multichassis link aggregation group (multi-LAG) feature, which provides flexibility in connecting the controller to a switch's infrastructure, is supported.

You can connect a LAG to a single switch. However, different VLANs is connected to different LAGs. The redundancy port is connected to the same distribution switch as the uplinks or directly connected in a back-to-back configuration.

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

Supported topologies are network deployment configurations. They define how Cisco Catalyst 9800 series controllers connect with the network through their available ports and set limitations regarding mixing port types and minimum group sizes for link aggregation.

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. Multi-LAGs can only include ports with matching capabilities, such as 2.5 G with 2.5 G, or 10 G with 10 G ports. You cannot include both a 2.5 G port and a 10 G port in a port channel group. Each group must have a minimum of two ports in one LAG.