EtherChannel Configuration - dummies

By Edward Tetz

EtherChannel has been a part of the Cisco IOS for many years, so you should find that all your switches support it with proper configuration. Do not be afraid to enable it on a pair of ports and try it.

When setting up an EtherChannel connection, remember the following points; they can help you avoid problems during the configuration process:

  • You can configure up to eight ports, and all of these ports should be the same type (Fast Ethernet, Gigabit Ethernet).

  • Set all ports to function at the same Speed and Duplex settings.

  • Ensure that all ports are enabled and that none have been configured using the shutdown command.

  • Switchport settings from the first port in EtherChannel are copied to all other ports in the EtherChannel when the ports are added to the channel group. This is a copy action and not a link, so if you change the settings after the fact, you need to change the settings on all ports. The settings that must remain the same across all ports are

    • Allowed VLAN list

    • STP path cost

    • STP port priority

    • STP PortFast settings

    • EtherChannel groups

Cisco’s GigaStack, FlexStack, and other proprietary high speed inter-switch links should never be configured as part of an EtherChannel because these stacking ports have specific functionality enabled for stacking functions that is not compatible with EtherChannel. Only use standard connection ports on the front of your switch for EtherChannel connections.

The basic process for configuring your EtherChannel interfaces is as follows:

  1. Connect to the command-line interface (CLI) your switch.

    This connection may be via SSH, Telnet, or the console port.

  2. Access Privileged EXEC mode.

    Switch1> enable
  3. Access Global Configuration mode.

    Switch1# configure terminal 
  4. Access Interface Configuration mode.

    Switch1(config)# interface range fasttethernet0/11 -12 
  5. Change switchport to trunk or access, but all ports must be in the same VLAN.

    Switch1(config-if-range)# switchport mode access
    Switch1(config-if-range)# switchport access vlan 10
  6. Assign the port to a channel group, which is an integer between 1 and 6.

    You also configure PAgP or LCAP at this time by specifying a mode, as listed in the below table.

    Switch1(config-if-range)# channel-group 5 mode desirable 
  7. Use the end command to exit out of Global Configuration mode.

EtherChannel Modes
Mode Protocol Description
Auto PAgP Sets the interface to respond to PAgP negotiation packets, but
the interface will start negotiations on its own.
Desirable PAgP Sets the interface to actively attempt to negotiate a PAgP
On EtherChannel Forces the connection to bring all links up without using a
protocol to negotiate connections. This mode can only connect to
another device that is also set to on. When using this mode, the
switch does not negotiate the link using either PAgP or LACP.
Active LACP Sets the interface to actively attempt to negotiate connections
with other LACP devices.
Passive LACP Sets the interface to respond to LACP data if it receives
negotiation requests from other systems.

The following commands are the setup commands you use for configuring one of the switches for EtherChannel. Notice the keyword “desirable,” which means that you will be using the Cisco proprietary protocol of PAgP. This also means that the switch at the other end of the connections needs to be a Cisco switch as well.

Switch1> enable
Switch1# configure terminal 
Switch1(config)# interface range fasttethernet0/11 -12 
Switch1(config-if-range)# switchport mode access
Switch1(config-if-range)# switchport access vlan 10
Switch1(config-if-range)# channel-group 5 mode desirable 
Switch1(config-if-range)# end 

Note that on the second switch, you applied the following configuration. Notice that the channel-group used on this switch is different. Different port groups are allowed because it is simply a local (to the switch) configuration to keep each port group uniquely identified. Many IT administrators do keep the channel-group numbers the same because by matching the port group numbers on either end of the connection, you can avoid confusion for others.

Switch2> enable
Switch2# configure terminal 
Switch2(config)# interface range fasttethernet0/1 -2 
Switch2(config-if-range)# switchport mode access
Switch2(config-if-range)# switchport access vlan 10
Switch2(config-if-range)# channel-group 2 mode auto 
Switch2(config-if-range)# end 

In this configuration, this pair of ports allows you to send data only for VLAN 10 over the EtherChannel link. To pass traffic for all VLANs, you must configure the switchport as a trunk because Access ports will only send traffic for one VLAN.