Understanding and configuring EtherChannels

Let's imagine you are connecting two switches using their GigabitEthernet interfaces; your objective is to combine the bandwidth of the two physical interfaces to get a total of 2 GB/s between the switches. Making the physical connections between both switches does not simply combine the bandwidth automatically. The following diagram shows a visual representation of the connection:

Figure 5.28 – Two switches connected together

Why is one link blocked between the switches? By default, Cisco switches have a layer 2 loop prevention protocol known as Spanning-Tree Protocol (STP). Therefore, physically interconnecting switches, as shown in the previous diagram, will cause STP to automatically block one of the interfaces.

This is where EtherChannels come in to save us once more. An EtherChannel allows us to combine multiple physical ports on a switch to create a single logical interface. Therefore, the...