Short Note on Etherchannel

Etherchannel is a technology that lets you bundle multiple physical links into a single logical link.We know if we connect two switches via one cable there will not be any loop and no need of STP.But if we connect two or more cables between two switches there will be chance for loops.In normal case STP will run and prevent formation of loops.But the problem is we cant add redundancy between switches.

Etherchannel can bundle all physical links into a logical link with the combined bandwidth.For example if there are 4 fast Ethernet cables between switch A and Switch B,by combining 4x 100 Mbit I now have a 400 Mbit link. Spanning tree sees this link as one logical link so there are no loops!

Etherchannel will do load balancing among the different links that we have and it takes care of redundancy. Once one of the links fails it will keep working and use the links that we have left.we can use upto 8 physical interface in one bundle

We can configure Etherchannel using two protocols
•  PAgP(Cisco proprietary)
•  LACP (IEEE standard)

These protocols can dynamically configure an etherchannel. It’s also possible to configure a static etherchannel without these protocols doing the negotiation of the link for you. PAgp and LACP will check if the configuration of the interfaces that you use are the same.If you are going to create an etherchannel you need to make sure that all ports have the same configuration:

•  Duplex has to be the same.
•  Speed has to be  same.
•  Same native AND allowed VLANs.
•  Same switchport mode (access or trunk).

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