Trying to understand Etherchannel

agtjamesb007

I am trying to understand Etherchannel.
STP is in use, to prevent redundant loops. But Etherchannel is utilized for load balancing.
So what data is able to travel down this Etherchannel in order to load balance that isn't being blocked by the STP?

EdTheLad

An etherchannel bundle is seen as a single link to STP, one link within the bundle is chosen as the ctrl link to send bpdu's down, this is typically the first link in the bundle, but it's really platform dependent. With STP the whole ethernet bundle i.e. all links are either forwarding or blocked.

_Gonzalo_

agtjamesb007 wrote: »

I am trying to understand Etherchannel.
STP is in use, to prevent redundant loops.

I think you are just confused with Etherchannel and STP interaction. To avoid this, think of just two switches:

If you have one single cable between them, STP would do nothing (no loops)
If you have two cables (that´s one loop) STP would block one of them. But now, we do not want any of them to be blocked, so we create an etherchannel and bundle them. This way, they would behave like only one single cable again (for most purposes, including STP operation)

Etherchannel load balancing is really not related to this interaction, but to how etherchannel manages data.

tecnodog7

_Gonzalo_ wrote: »

Etherchannel load balancing is really not related to this interaction, but to how etherchannel manages data.

So if I'm not mistaken, when you created a Etherchannel bundle it takes the two physical link and it then acts as one logical right link right? So if I have two 1 Gbps, I'm only getting the max of 1 Gbps (on both those ports ), but if we are suppose two computers connected to a switch and computer A is using port 1 for a major file transfer then Etherchannel will direct computer B to use port 2 right?

Does EtherChannel always work in conjunction with STP always? Does STP work on WAN Links too?
Also EtherChannel isn't a true sort to speak load balancer right?

My answer is Yes since we are talking about redundant links. But the WAN question still remains?

EdTheLad

Tecnodog7, maybe it's time to take a break from certs and learn some English?

tecnodog7

EdTheLad wrote: »

Tecnodog7, maybe it's time to take a break from certs and learn some English?

Wow, that was HARSH!!!
You hurt my feelings

verbhertz

An interesting fact about Etherchannel is that it is load balanced based on mac, ip, or ports. So you could have 4 links bundled together and potentially only ever be using one in a given direction, depending on the traffic being switched.

agtjamesb007

I wonder why a new loop is not created again? STP blocks the link. It only see's one link. There are say 4 physical links. 1 blocked link and 3 others to supply bandwidth. Why don't those other links negate what STP did and create another loop?

hurricane1091

Etherchannel is seen as a single path, hence why no loops are created. I think you are having a hard time understanding how STP can work here and that's reasonable.

Example: If Fa0/1 and Fa0/2 on two switches are used to connect each other via an etherchannel, you are looking at it as if a loop is possible. STP does not see this making a choice between Fa0/1 or Fa0/2 for which port needs to be blocked because it does not see it as two paths. It sees it as one path. So if SW1 send a broadcast out Fa0/1, SW2 isn't going to send a broadcast back through Fa0/2 since it is a part of the ether-channel - hence no loop. If you left the two links as not an etherchannel, STP would kick in and block a link between the two because a loop would be possible.

You could view Fa0/1 as really Fa0/1.5 and Fa0/2 as Fa0/1.5, it's the same link.

Hopefully that's accurate and makes sense. If not then I'm sure Ed will know. I was confused with this before and haven't really though about it recently. It also sounds like you're trying to imagine an etherchannel link between a switch and two computers, which makes no sense and is not how it works. Etherchannel can be used between two switches like in the example above though...

tecnodog7

Makes sense hurricane.

_Gonzalo_

tecnodog7 wrote: »

So if I have two 1 Gbps, I'm only getting the max of 1 Gbps (on both those ports ), but if we are suppose two computers connected to a switch and computer A is using port 1 for a major file transfer then Etherchannel will direct computer B to use port 2 right?

You cannot have an etherchannel formed when two links are connected to two different devices (except if stacked, but no need to go down this path now...)

tecnodog7 wrote: »

Does EtherChannel always work in conjunction with STP always?

STP is always there, so that´d be a yes. But I believe that you meant to ask something more with this question. Anyway, keep the original idea, which by the way is correct:

"So if I'm not mistaken, when you created a Etherchannel bundle it takes the two physical link and it then acts as one logical right link right?"

tecnodog7 wrote: »

Does STP work on WAN Links too?

ETHERchannel suggests it by itself, don´t you think? Only Ethernet.

tecnodog7 wrote: »

Also EtherChannel isn't a true sort to speak load balancer right?

It is. I don´t remember how it balances traffic, but I believe it to be round robin. I´m sure someone will be able to confirm it (or you could google it )