Can one of you pros explain EhterChannel/Link Aggregation to me?

zrockstar

Hey guys, I am studying for my CCNA right now, and I ran across EtherChannel in my LAN switching book. It gave a brief description of what it does and said that a full discussion of link aggregation is beyond the scope of CCNA, so I was just hoping one of you guys could satisfy my curiosity. I know link aggregation will take up to 8 ports and combine their port speeds for faster transmission, but wouldn't STP just shut down all but one of them? Or are there separate commands in the switch dedicated for EtherChannel where it will load balance across the designated ether channel links? Thanks.

Forsaken_GA

No. When you bind ports together into an port channel, it creates a new logical interface consisting of all the links aggregated. That interface is what is in STP, not the individual links that make it up.

Moeeed

zrockstar wrote: »

Hey guys, I am studying for my CCNA right now, and I ran across EtherChannel in my LAN switching book. It gave a brief description of what it does and said that a full discussion of link aggregation is beyond the scope of CCNA, so I was just hoping one of you guys could satisfy my curiosity. I know link aggregation will take up to 8 ports and combine their port speeds for faster transmission, but wouldn't STP just shut down all but one of them? Or are there separate commands in the switch dedicated for EtherChannel where it will load balance across the designated ether channel links? Thanks.

You definitely do not need it for CCNA.


So here I assume that you have studied a bit of STP (802.1d) normal spanning tree.


SW_A ========== SW_B

according to STP, one of the ports on SW_B (assuming that A has lower MAC and bridge priority) will be in blocking state.

There for if data is going from a host on SW_A to a Host on SW_B, it will ONLY use one port. (since one port is Root Port, and the other is in blocking state).

With EtherChannel you can bundle the 2 links (up to 8 ) and make it act like ONE Link.

This way both the links are open and sending traffic.

so with EtherChannel, the LINK on SW_B will be the Root Port and on SW_A it will be Designated Forwarding port.

The second part of the questions is also another manipulation. You can change the way the data is send across the ether channel. destination-Source MAC or source-Destination MAC. Keep in mind its for Layer 2 EtherChannel.

zrockstar

Excellent, thank you guys. I did a little bit of reading on configs, and it seems like channel-group is really the only non-CCNA command. If that is the case, EtherChannel should be part of CCNA in my opinion, as it seems like the logical way to go switch to switch.