How to configure EtherChannel ?

Previous post describes how EtherChannel works and why we use it.  
Take a look here

Now we’ll discuss how to configure EtherChannel.

As we seen before, we can bundle up to 8 physical interfaces. We must bind the number of physical interfaces into one logical interface (Channel).  Most of the Cisco switches support 64 channels. Single channel can bind min 2 to max 8 physical interfaces.

PAgP and LACP are the two different Protocols which facilitates the automatic creation of EtherChannels by Exchanging packets between Ethernet interfaces.

PAgP is a Cisco proprietary protocol whereas LACP is an open standard protocol 802.3ad

Two types of EtherChannel Configuration:

1.       1. Layer 3 Configuration: In Layer 3 EtherChannel Configuration, first we must create a logical interface which is call Port-Channel. Then we add the physical interfaces to the Port-Channel.

Example to create a Port-Channel:

Router# configure terminal

Router(config)# interface port-channel 6    (port-channel number 1-64)

Router(config-if)# ip address 10.0.0.1 255.0.0.0

Router(config-if)# exit

Router(config)# exit

Router# show running-config interface port-channel 6  (to verify the port-channel configuration)

We created a port-channel successfully. Now we must add the physical interfaces to this port-channel 6.

Router# configure terminal

Router(config)# interface range fastethernet 1/1 -2

Router(config-if)# no ip address

Router(config-if)# channel-group group 6 mode desirable  (by-defalut Cisco devices use PAgP)

Router(config-if)# exit

Router# show running-config interface fastethernet 1/1  (to verify interface 1 configuration)

 Router# show interfaces fastethernet 1/1 etherchannel

2.       2. Layer 2 Configuration:  Command varies in Layer 2. We manually created port-channel in Layer 3, but in Layer 2 we must create a channel-group which automatically assigns logical port-channel.

Example to create a channel-group:

Switch(config)#interface range fastethernet 1/1 - 4

Switch (config-if-range)#channel-group 1 mode on    (Port 1/1-4 assigned to port-channel)

Switch (config-if-range)#switchport

Switch (config-if-range)#switchport trunk encapsulation dot1q

Switch (config-if-range)#switchport mode trunk

Switch #show interfaces port-channel 1

Switch #show etherchannel 1 summary

In the above example we assigned the ports as trunk. The ports with in a EtherChannel must be in trunk mode or in a single VLAN.

Whatever change of configurations made on port-channel must affect all the ports within the channel, but configuring an interface (port) only affects the particular interface not the port-channel.