What is EtherChannel?

EtherChannel is a link aggregation technology used primarily on Cisco switches. It can bundle two to eight physical port of the same Ethernet media type and speed. All bundled ports must have similar configuration.
EtherChannel can be used to increase bandwidth, provide redundancy and load balance traffic

EtherChannel Negotiation Protocols

Cisco supports two EtherChannel negotiation protocols. They are used to provide automatic EtherChannel configuration and negotiation between switches.

  1. Port Aggregation Protocol (PAgP) – Cisco proprietary negotiation protocol
  2. Link Aggregation Control Protocol (LACP) – standard based alternative to PagP defined in IEEE 802.3ad

Scenario

Suppose Switch SW1 and SW2 are connected to each other via

  • SW1 fa1/1 to SW2 fa1/1
  • SW1 fa1/2 to SW2 fa1/2
  • SW1 fa1/3 to SW2 fa1/3

We are required to make an EtherChannel using port fa1/1, fa1/2 and fa1/3

Configuring EtherChannel using LACP

In the configuration example we will be using Link Aggregation Control Protocol (LACP) for negotiation protocol

Because the ports used in both switches are identical, same configuration can be used on switch SW1 and SW2.
Configure ports on SW1 with LACP as negotiation protocol

SW1(config)#interface range fastEthernet 1/1 - 3
SW1(config-if-range)#no shutdown
SW1(config-if-range)# channel-protocol lacp
SW1(config-if-range)# channel-group 1 mode active
Creating a port-channel interface Port-channel 1

Configure ports on SW2

SW2(config)#interface range fastEthernet 1/1 - 3
SW2(config-if-range)#no shutdown
SW2(config-if-range)#channel-protocol lacp
SW2(config-if-range)#channel-group 1 mode active
Creating a port-channel interface Port-channel 1

Now if we check the interfaces, there should be a new interface called Port-channel1

SW1#show ip interface brief
...
FastEthernet1/11           unassigned      YES unset  up                    down
FastEthernet1/12           unassigned      YES unset  up                    down
FastEthernet1/13           unassigned      YES unset  up                    down
FastEthernet1/14           unassigned      YES unset  up                    down
FastEthernet1/15           unassigned      YES unset  up                    down
Port-channel1              unassigned      YES unset  up                    up
...

Thats it for the configuration part

Verifying EtherChannel Configuration

Use the following command to verify EtherChannel status

SW1# show etherchannel summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+---------------------------------
1      Po1(SU)         LACP      Fa1/1(P)   Fa1/2(P)   Fa1/3(P)

Interesting Fact

EtherChannel technology was invented by Kalpana in the early 1990s and was later acquired by Cisco Systems in 1994. In 2000 the IEEE passed 802.3ad, an open standard of EtherChannel (LACP).