First we need to understand what is Etherchannel and why we use it.Actually this is a technique in which we combine two physical interface(ethernet ports) of cisco switch and use them as one single logical interface(port).
In this way we can combine bandwidth of multiple ports.It also provides redundancy because if any port fails then still there is no connection loss.One port fails other port will still active and will provide communication and hence provide redundancy.
ETHERCHANNEL is actualy a port link aggregation technology or in other word you can say ETHERCHANNEL is a port-channel architecture in which you can see a bundle of multiple physical links working as a single logical link.
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If we combine fa0/3 and fa0/4 interfaces each providing bandwidth of 100Mbs.
The total bandwidth of logical port will be 200Mbs.
This is what we call Link Aggregation.
Etherchannel technique is known as NIC Teaming in Windows and Ethernet Bridging in Linux.
Now I am going to configure Ether channel and for this we need atleast two ethernet ports.
Ether channel Configuration on switch0 :
Switch>enable Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#host switch0 switch0(config)#int range fa0/3-4 switch0(config-if-range)#channel-group 1 mode on switch0(config-if-range)#exit switch0(config)#interface port-channel 1 switch0(config-if)#switchport mode trunk
ether channel configuration on switch1:
Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#host switch1 switch1(config)#int range fa0/3-4 switch1(config-if-range)#channel-group 1 mode on switch1(config-if-range)#exit switch1(config)#interface port-channel 1 switch1(config-if)#switchport mode trunk
Check ether channel configuration;
switch1#show etherchannel summary Flags: D - down P - 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 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) - Fa0/3(P) Fa0/4(P)