In a world with no redundancy, your workstation sends a packet to the IP address of the server on the same network. The workstation checks its arp table doesn't see the address, arps for it to get the mac address and sends the packet. At this point the switch *should* know of the mac address of the server.

The switch looks at it's table and either says, "i know where that mac is" and forwards it out the right port or, it says, "i don't know where that mac is" and forwards it out all ports but the one the packet came in on. The assumption is the server replied to the arp and from that point on the switch knows what port to send stuff to that server on.

Now, introduce etherchannel. Now you have one logical bundling of multiple physical links and, behind each link a different nic in the same server each with it's own mac address but sharing an IP address. Basically we've used etherchannel to create redundancy.

So now what happens? The workstation arps, the server replies, the switch learns and presumably associates that mac with both physical ports because it looks like one logical port. But as the nics load balance, one of two different macs could be replying every time at the layer 2.

How does the switch distinguish which port or ports to ship packets to the server on? Would we expect to see a lot of flooding of packets or would the switch store both of the server nic's mac addresses to the single ether channel and only send packets out both of those ports or...?

I find this confusing.