EtherChannel provides fault-tolerant high-speed links between switches, routers, and servers. You can use the EtherChannel to increase the bandwidth between the wiring closets and the data center, and you can deploy it anywhere in the network where bottlenecks are likely to occur. EtherChannel provides automatic recovery for the loss of a link by redistributing the load across the remaining links. If a link fails, EtherChannel redirects traffic from the failed link to the remaining links in the channel without intervention.

An EtherChannel consists of individual Ethernet links bundled into a single logical link.

Figure 1. Typical EtherChannel Configuration

The EtherChannel provides full-duplex bandwidth up to 8 Gb/s (Gigabit EtherChannel) or 80 Gb/s (10-Gigabit EtherChannel) between your switch and another switch or host.

Each EtherChannel can consist of up to eight compatibly configured Ethernet ports.

The number of EtherChannels is limited to 128.

The LAN Base feature set supports up to 24 EtherChannels.

All ports in each EtherChannel must be configured as either Layer 2 or Layer 3 ports. The EtherChannel Layer 3 ports are made up of routed ports. Routed ports are physical ports configured to be in Layer 3 mode by using the no switchport interface configuration command. For more information, see the Configuring Interface Characteristics chapter.

An EtherChannel comprises a channel group and a port-channel interface. The channel group binds physical ports to the port-channel interface. Configuration changes applied to the port-channel interface apply to all the physical ports bound together in the channel group.

Figure 4. Relationship of Physical Ports, Channel Group and Port-Channel Interface.

The channel-group command binds the physical port and the port-channel interface together. Each EtherChannel has a port-channel logical interface numbered from 1 to 128. This port-channel interface number corresponds to the one specified with the channel-group interface configuration command.

• With Layer 2 ports, use the channel-group interface configuration command to dynamically create the port-channel interface.

  You also can use the interface port-channel port-channel-number global configuration command to manually create the port-channel interface, but then you must use the channel-group channel-group-number command to bind the logical interface to a physical port. The channel-group-number can be the same as the port-channel-number, or you can use a new number. If you use a new number, the channel-group command dynamically creates a new port channel.

• With Layer 3 ports, you should manually create the logical interface by using the interface port-channel global configuration command followed by the no switchport interface configuration command. You then manually assign an interface to the EtherChannel by using the channel-group interface configuration command.

• With Layer 3 ports, use the no switchport interface command to configure the interface as a Layer 3 interface, and then use the channel-group interface configuration command to dynamically create the port-channel interface.

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

By using PAgP, the device or device 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.

The LACP is defined in IEEE 802.3ad and enables Cisco devices to manage Ethernet channels between devices that conform to the IEEE 802.3ad protocol. LACP facilitates the automatic creation of EtherChannels by exchanging LACP packets between Ethernet ports.

By using LACP, the device or device stack learns the identity of partners capable of supporting LACP and the capabilities of each port. It 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. For example, LACP 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, LACP adds the group to the spanning tree as a single device port.

The independent mode behavior of ports in a port channel is changed. With CSCtn96950, by default, standalone mode is enabled. When no response is received from an LACP peer, ports in the port channel are moved to suspended state.

EtherChannel on mode can be used to manually configure an EtherChannel. The on mode forces a port to join an EtherChannel without negotiations. The on mode can be useful if the remote device does not support PAgP or LACP. In the on mode, a usable EtherChannel exists only when the devices at both ends of the link are configured in the on mode.

Ports that are configured in the on mode in the same channel group must have compatible port characteristics, such as speed and duplex. Ports that are not compatible are suspended, even though they are configured in the on mode.

Caution

You should use care when using the on mode. This is a manual configuration, and ports on both ends of the EtherChannel must have the same configuration. If the group is misconfigured, packet loss or spanning-tree loops can occur.

EtherChannel balances the traffic load across the links in a channel by reducing part of the binary pattern formed from the addresses in the frame to a numerical value that selects one of the links in the channel. You can specify one of several different load-balancing modes, including load distribution based on MAC addresses, IP addresses, source addresses, destination addresses, or both source and destination addresses. The selected mode applies to all EtherChannels configured on the device.

Note

Layer 3 Equal-cost multi path (ECMP) load balancing is based on source IP address, destination IP address, source port, destination port, and layer 4 protocol. Fragmented packets will be treated on two different links based on the algorithm calculated using these parameters. Any changes in one of these parameters will result in load balancing.

You configure the load-balancing and forwarding method by using the port-channel load-balance and the port-channel load-balance extendedglobal configuration commands.

If a stack member that has ports participating in an EtherChannel fails or leaves the stack, the active device removes the failed stack member device ports from the EtherChannel. The remaining ports of the EtherChannel, if any, continue to provide connectivity.

When a device is added to an existing stack, the new device receives the running configuration from the active device and updates itself with the EtherChannel-related stack configuration. The stack member also receives the operational information (the list of ports that are up and are members of a channel).

When two stacks merge that have EtherChannels configured between them, self-looped ports result. Spanning tree detects this condition and acts accordingly. Any PAgP or LACP configuration on a winning device stack is not affected, but the PAgP or LACP configuration on the losing device stack is lost after the stack reboots.

If improperly configured, some EtherChannel ports are automatically disabled to avoid network loops and other problems. Follow these guidelines to avoid configuration problems:

• Do not try to configure more than 128 EtherChannels on the device or device stack.

• Configure a PAgP EtherChannel with up to eight Ethernet ports of the same type.

• Configure a LACP EtherChannel with up to 16 Ethernet ports of the same type. Up to eight ports can be active, and up to eight ports can be in standby mode.

• Configure all ports in an EtherChannel to operate at the same speeds and duplex modes.

• Enable all ports in an EtherChannel. A port in an EtherChannel that is disabled by using the shutdown interface configuration command is treated as a link failure, and its traffic is transferred to one of the remaining ports in the EtherChannel.

• When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, you must also make the changes to all ports in the group:

  • Allowed-VLAN list

  • Spanning-tree path cost for each VLAN

  • Spanning-tree port priority for each VLAN

  • Spanning-tree Port Fast setting

• Do not configure a port to be a member of more than one EtherChannel group.

• Do not configure an EtherChannel in both the PAgP and LACP modes. EtherChannel groups running PAgP and LACP can coexist on the same device or on different devices in the stack. Individual EtherChannel groups can run either PAgP or LACP, but they cannot interoperate.

• Do not configure a secure port as part of an EtherChannel or the reverse.

• Do not configure a port that is an active or a not-yet-active member of an EtherChannel as an IEEE 802.1x port. If you try to enable IEEE 802.1x on an EtherChannel port, an error message appears, and IEEE 802.1x is not enabled.

• If EtherChannels are configured on device interfaces, remove the EtherChannel configuration from the interfaces before globally enabling IEEE 802.1x on a device by using the dot1x system-auth-control global configuration command.

• If cross-stack EtherChannel is configured and the device stack partitions, loops and forwarding issues can occur.

The auto-LAG feature provides the ability to auto create EtherChannels on ports connected to a switch. By default, auto-LAG is disabled globally and is enabled on all port interfaces. The auto-LAG applies to a switch only when it is enabled globally.

On enabling auto-LAG globally, the following scenarios are possible:

• All port interfaces participate in creation of auto EtherChannels provided the partner port interfaces have EtherChannel configured on them. For more information, see the "The supported auto-LAG configurations between the actor and partner devices" table below.

• Ports that are already part of manual EtherChannels cannot participate in creation of auto EtherChannels.

• When auto-LAG is disabled on a port interface that is already a part of an auto created EtherChannel, the port interface will unbundle from the auto EtherChannel.

The following table shows the supported auto-LAG configurations between the actor and partner devices:

On disabling auto-LAG globally, all auto created Etherchannels become manual EtherChannels.

You cannot add any configurations in an existing auto created EtherChannel. To add, you should first convert it into a manual EtherChannel by executing the port-channel<channel-number>persistent.

Note	Auto-LAG uses the LACP protocol to create auto EtherChannel. Only one EtherChannel can be automatically created with the unique partner devices.

1.    configure terminal


2.    interface interface-id


3.    switchport mode {access | trunk}


4.    switchport access vlan vlan-id


5.    channel-group channel-group-number mode {auto [non-silent] | desirable [non-silent ] | on } | { active | passive}


6.    end

Device# configure terminal

Device(config)# interface gigabitethernet2/0/1

Device(config-if)# switchport mode access

Device(config-if)# switchport access vlan 22

Device(config-if)# channel-group 5 mode auto

Device(config-if)# end

1.    enable


2.    configure terminal


3.    interface interface-id


4.    no ip address


5.    no switchport


6.    channel-group channel-group-number mode { auto [ non-silent ] | desirable [ non-silent ] | on } | { active | passive }


7.    end

Device> enable

Device# configure terminal

Device(config)# interface gigabitethernet 1/0/2

Device(config-if)# no ip address

Device(config-if)# no switchport

Device(config-if)# channel-group 5 mode auto
               

Device(config-if)# end

1.    configure terminal


2.    port-channel load-balance { dst-ip | dst-mac | dst-mixed-ip-port | dst-port | extended [dst-ip | dst-mac | dst-port | ipv6-label | l3-proto | src-ip | src-mac | src-port ] | src-dst-ip | src-dst-mac src-dst-mixed-ip-port src-dst-portsrc-ip | src-mac | src-mixed-ip-port | src-port}


3.    end

Device# configure terminal

Device(config)# port-channel load-balance src-mac

Device(config)# end

1.    configure terminal


2.    port-channel load-balance extended [ dst-ip | dst-mac dst-port | ipv6-label | l3-proto | src-ip | src-mac | src-port ]


3.    end

Device# configure terminal

Device(config)# port-channel load-balance extended dst-ip dst-mac src-ip

Device(config)# end

1.    configure terminal


2.    interface interface-id


3.    pagp learn-method physical-port


4.    pagp port-priority priority


5.    end

Device# configure terminal

Device(config)# interface gigabitethernet 1/0/2

Device(config-if)# pagp learn-method physical port

Device(config-if)# pagp port-priority 200

Device(config-if)# end

When LACP is enabled, the software, by default, tries to configure the maximum number of LACP-compatible ports in a channel, up to a maximum of 16 ports. Only eight LACP links can be active at one time; the remaining eight links are placed in hot-standby mode. If one of the active links becomes inactive, a link that is in the hot-standby mode becomes active in its place.

You can override the default behavior by specifying the maximum number of active ports in a channel, in which case, the remaining ports become hot-standby ports. For example, if you specify a maximum of five ports in a channel, up to 11 ports become hot-standby ports.

If you configure more than eight links for an EtherChannel group, the software automatically decides which of the hot-standby ports to make active based on the LACP priority. To every link between systems that operate LACP, the software assigns a unique priority made up of these elements (in priority order):

• LACP system priority

• System ID (the device MAC address)

• LACP port priority

• Port number

In priority comparisons, numerically lower values have higher priority. The priority decides which ports should be put in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating.

Determining which ports are active and which are hot standby is a two-step procedure. First the system with a numerically lower system priority and system ID is placed in charge of the decision. Next, that system decides which ports are active and which are hot standby, based on its values for port priority and port number. The port priority and port number values for the other system are not used.

You can change the default values of the LACP system priority and the LACP port priority to affect how the software selects active and standby links.

1.    enable


2.    configure terminal


3.    interface { fastethernet | gigabitethernet | tengigabitethernet} slot/port


4.    lacp rate { normal | fast }


5.    end


6.    show lacp internal

Device> enable

Device# configure terminal

Device(config)# interface gigabitEthernet 2/1

Device(config-if)# lacp rate fast

Device(config)# end

Device# show lacp internal
Device# show lacp counters

1.    enable


2.    configure terminal


3.    [no] port-channel auto


4.    end


5.    show etherchannel auto

Device> enable

Device# configure terminal

Device(config)# port-channel auto 

Device(config)# end

Device# show etherchannel auto

1.    enable


2.    configure terminal


3.    interface interface-id


4.    [no] channel-group auto


5.    end


6.    show etherchannel auto

Device> enable

Device# configure terminal

Device(config)# interface gigabitethernet 1/0/1 

Device(config-if)# channel-group auto

Device(config-if)# end

Device# show etherchannel auto

1.    enable


2.    port-channel channel-number persistent


3.    show etherchannel summary

Device> enable

Device# port-channel 1 persistent

Device# show etherchannel summary