Auto-LAG feature:

• Automatically creates EtherChannels on ports connected to a switch.

• Uses the LACP (Link Aggregation Control Protocol) to create auto EtherChannels.

• Supports only one EtherChannel per unique partner device.

• Disabled globally by default, but is enabled on all port interfaces.

• Requires global enablement for Auto-LAG to operate. Ports must also meet specific conditions:

  • Ports with existing manual EtherChannels cannot participate in auto EtherChannel creation.

  • Disabling Auto-LAG on a port causes it to unbundle from any auto-created EtherChannel.

• Global disablement results in all existing auto-created EtherChannels being converted into manual EtherChannels.

When Auto-LAG is globally enabled, the following configurations are supported between actor and partner devices:

Follow these guidelines when configuring the auto-LAG feature:

• Auto-LAG is enabled on interfaces by default. If enabled globally on the switch, the user wants some ports not to participate in becoming an auto EtherChannel member. Disable the auto-LAG on those port

• A port interface will not bundle to an auto EtherChannel when it is already a member of a manual EtherChannel. To allow it to bundle with the auto EtherChannel:

  • First unbundle the manual EtherChannel on the port interface.

• When auto-LAG is enabled and auto EtherChannel is created:

  • You can create multiple EtherChannels manually with the same partner device.

  • By default, the port tries to create auto EtherChannel with the partner device.

• Auto-LAG is supported only on Layer 2 EtherChannel and is not supported on:

  • Layer 3 interfaces

  • Layer 3 EtherChannel.

• Auto-LAG is supported on cross-stack EtherChannel.

A Link Aggregation Control Protocol (LACP) is a network protocol defined under the IEEE 802.3ad standard that:

• Facilitates the automatic creation of EtherChannels by exchanging LACP packets between Ethernet ports,

• Enables devices to dynamically group similarly configured ports into a single logical link (channel or aggregate port), and

• Ensures compatibility between networking devices that support the IEEE 802.3ad protocol.

LACP identifies ports capable of supporting LACP and their capabilities. Ports are dynamically grouped into an EtherChannel based on hardware, administrative, and port parameter constraints such as:

• Speed,

• Duplex mode,

• Native VLAN, and

• Trunking status and type.

Once grouped, LACP adds the EtherChannel to the spanning tree protocol as a single device port. In default standalone mode, ports that do not receive a response from an LACP peer are moved to a suspended state. This ensures compatibility and stability in connected devices.

LACP modes specify whether a port can send LACP packets or only receive LACP packets.

Both the active and passive LACP modes enable ports to negotiate with partner ports to an EtherChannel based on criteria such as port speed, and for Layer 2 EtherChannels, based on trunk state and VLAN numbers.

Ports can form an EtherChannel when they are in different LACP modes as long as the modes are compatible. For example:

• A port in the active mode can form an EtherChannel with another port that is in the active or passive mode.

• A port in the passive mode cannot form an EtherChannel with another port that is also in the passive mode because neither port starts LACP negotiation.

When one end of an EtherChannel has more members than the other, the unmatched ports enter the standalone state. The standalone mode is also called the independent mode. In the standalone mode the port is not bundled in an EtherChannel. The port functions as a standalone data port and it can send and receive BPDUs and data traffic.

In a topology that is not protected from Layer 2 loops by the spanning tree protocol (STP), a port in the standalone state can cause significant network errors. You can enter the port-channel standalone-disable command in the interface configuration mode to put ports into the suspended state instead of the standalone state.

The standalone mode is particularly relevant when a port (A) in a Layer 2 LACP EtherChannel is connected to an unresponsive port (B) on the peer. When LACP standalone is disabled on the EtherChannel, all traffic arriving on A is blocked (the default behavior on a switch). In some scenarios, you might want to allow management traffic on such ports. You can do this by enabling LACP standalone (or independent) mode. To enable the standalone mode on a Layer 2 LACP Etherchannel, use the no port-channel standalone disable command in the interface configuration mode. To disable the Standalone mode and revert to the default use the port-channel standalone disable command in the interface configuration mode.

Note	LACP standalone mode is disabled by default.

Starting with the Cisco IOS XE Dublin 17.10.1 release, you can configure the LACP standalone mode on a Layer 3 EtherChannel. To configure the standalone mode use the no port-channel standalone disable command in the interface configuration mode. To disable the Standalone mode and revert to the default use the port-channel standalone disable command in the interface configuration mode.

LACP port-channel operation, bandwidth availability, and link redundancy can be further refined with the LACP port-channel min-links and the LACP max-bundle features.

The LACP port-channel min-links feature:

• Configures the minimum number of ports that must be linked up and bundled in the LACP port channel.

• Prevents a low-bandwidth LACP port channel from becoming active.

• Causes an LACP port channel to become inactive if there are too few active members ports to supply the required minimum bandwidth.

The LACP max-bundle feature:

• Defines an upper limit on the number of bundled ports in an LACP port channel.

• Allows hot-standby ports with fewer bundled ports. For example, in an LACP port channel with five ports, you can specify a max-bundle of three, and the two remaining ports are designated as hot-standby ports.

The Link Aggregation Control Protocol (LACP) is a network protocol that:

• combines multiple physical ports into a single logical channel for redundancy,

• operates at the data link layer to enable fast convergence and failover, and

• synchronizes state information across member ports in active or passive mode.

Note	Layer 2 port channel the default load balancing is source MAC and destination MAC Layer 3 port channel the default load balancing is source IP and destination IP.

DTP and CDP send and receive packets over the physical ports in the EtherChannel.

Trunk ports send and receive LACP PDUs on the lowest-numbered VLAN.

In Layer 2 EtherChannels, the first port in the channel that comes up provides its MAC address to the EtherChannel. If this port is removed from the bundle, the next active port provides its MAC address.

In Layer 3 EtherChannels, the MAC address is allocated by the active device when the EtherChannel interface is created using the interface port-channel global configuration command.

The LACP 1:1 Redundancy feature supports an EtherChannel configuration with one active link, and fast switchover to a hot-standby link. The link that is connected to the port with the lower port priority number (and therefore, of a higher priority) will be the active link, and the other link will be in a hot-standby state. If the active link goes down, LACP performs a fast switchover to the hot-standby link to keep the EtherChannel up. When the failed link becomes operational again, LACP performs another fast switchover to revert to the original active link.

To allow the higher priority port to stabilize when it becomes active again after a higher-priority to lower-priority switchover, the LACP 1:1 Hot Standby Dampening feature configures a timer that delays switchover back to the higher priority port after higher priority port becomes active.

The Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that can be run only on Cisco devices and on those devices that are licensed by vendors to support PAgP. PAgP facilitates the automatic creation of EtherChannels by exchanging PAgP packets between Ethernet ports.

By using PAgP, the switch or switch stack learns the identity of partners capable of supporting PAgP and the capabilities of each port. It then dynamically groups similarly configured ports (on a single device in the stack) into a single logical link (channel or aggregate port). Similarly configured ports are grouped based on hardware, administrative, and port parameter constraints. For example, PAgP groups the ports with the same speed, duplex mode, native VLAN, VLAN range, and trunking status and type. After grouping the links into an EtherChannel, PAgP adds the group to the spanning tree as a single device port.

If your switch is connected to a partner that is PAgP-capable, you can configure the switch port for nonsilent operation by using the non-silent keyword. If you do not specify non-silent with the auto or desirable mode, silent mode is assumed.

Use the silent mode when the switch is connected to a device that is not PAgP-capable and seldom, if ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not generating traffic. In this case, running PAgP on a physical port that is connected to a silent partner prevents that switch port from ever becoming operational. However, the silent setting allows PAgP to operate, to attach the port to a channel group, and to use the port for transmission.