To increase bandwidth on a given Cisco network device, typically etherchannel technology is used to accomplish this task. In most scenarios, etherchannel is used between two switches to provide additional bandwidth to the uplink connections. In less common instances, Network cards in servers that have drivers supporting the proprietary technology will be configured for etherchannel. The requirement is usually to increase bandwidth available on a link between two devices.

Etherchannel has not been used nearly as much for such requirements as redundancy, because there is a limitation on all the interfaces that belongs to an etherchannel group, each interface has to be plugged into the same switch. The stackable 3750 switches have allowed a little more redundant ability, in the sense that you can have two switches stacked via the stackwise ports in the back of the switch, which basically extends the backplane. By doing this, you are allowed to have an Etherchannel interface plugged into two different switches (as long as they are stacked). Let’s take a look at an example diagram for clarification:

Let’s take a look at the router configuration to accomplish the task of adding bandwidth.

interface Port-channel1
ip address 192.168.50.1 255.255.255.0
!
interface FastEthernet0/0
duplex full
speed 100
channel-group 1
!
interface FastEthernet0/1
duplex full
speed 100
channel-group 1

Next, the switch configuration:

interface Port-Channel1
switchport
switchport access vlan 10
switchport mode access
!
interface FastEthernet0/1
switchport
switchport access vlan 10
switchport mode access
channel-group 1 mode on
!
interface FastEthernet0/2
switchport
switchport access vlan 10
switchport mode access
channel-group 1 mode on

This example is configured for etherchannel without also being configured as a trunk (which means the aggregated interfaces are in access mode).

Another common configuration that goes along with etherchannel interfaces is Vlan Trunking. The term ‘trunking’ is often misused when referring to etherchannel use. When discussing a trunk, the meaning is an interface that carries multiple vlans across it. The terms trunking and etherchannel do not automatically go with each other.

The following example shows the same Etherchannel configuration as above, only this time the interfaces will also be configured as trunks in order to carry multiple vlans across the link(in this example – vlan 2,3,4,5,6, and 999).

First, the router configuration:

interface Port-channel1
 no ip address
!
interface Port-channel1.2
 encapsulation dot1Q 2
 ip address 192.168.2.1 255.255.255.0
!
interface Port-channel1.3
 encapsulation dot1Q 3
 ip address 192.168.3.1 255.255.255.0
!
interface Port-channel1.4
 encapsulation dot1Q 4
 ip address 192.168.4.1 255.255.255.0
!
interface Port-channel1.5
 encapsulation dot1Q 5
 ip address 192.168.5.1 255.255.255.0
!
interface Port-channel1.6
 encapsulation dot1Q 6
 ip address 192.168.6.1 255.255.255.0
!
interface Port-channel1.999
 encapsulation dot1Q 999 native
!
interface FastEthernet0/0
duplex full
speed 100
channel-group 1
!
interface FastEthernet0/1
duplex full
speed 100
channel-group 1

Here is the switch configuration:

interface Port-Channel1
switchport
switchport trunk allowed vlan 2,3,4,5,6,999
switchport mode trunk
!
interface FastEthernet0/1
switchport
switchport trunk allowed vlan 2,3,4,5,6,999
switchport mode trunk
channel-group 1 mode on
!
interface FastEthernet0/2
switchport
switchport trunk allowed vlan 2,3,4,5,6,999
switchport mode trunk
channel-group 1 mode on