A virtual MAC will be created for that link.
You may find the link is not dynamically load-balanced. The first device to use the etherchannel will use link 1, the second device
will use link 2, 3rd device will use link 1, 4th device- link2, etc, etc.
The link determination can be made using the source mac or the destination mac- configurable depending on your needs.
It creates some redundancy and higher capacity. It does not create always create more throughput for a single device, but will increase throughput for the network, as spanning-tree won't block the second port.
Example:
Server1 and Server2 connected to Switch1. Switch1 connected to Switch2 via etherchannel on ports 1 and 2. TRaffic from Server1 going to Switch2 will use port1, traffic from Server2 will use port2.
Each server only gets 100Mbps instead of 200, so the throughput of a single device isn't changed, however, the total throughput of the connection between Switch1 and Switch2 is 200Mbps.
Much of this depends on the switch and software running. Later switches and software allow for dynamic load-balancing of the links, but some require an odd number of links (3,5...) to do so (IIRC, the 3750s did this at one time).
Research the details of etherchannel for your switch and software to determine how it will function.
The more advanced the switch, the more capabilities it has. A 2924 or 2950 won't dynamically load-balance, like the larger switches can.
Take this with a grain of salt... its been a few years since I've used etherchannel, so Cisco may have changed things.
Either way, its a good solution but it can appear that things aren't working as expected if you don't research how your particular switches will handle things.
