Link aggregation protocols define how multiple physical network links are combined into a single logical connection, with IEEE 802.3ad serving as the industry standard and Cisco's EtherChannel as a widely deployed proprietary implementation. This content covers the distinctions between LACP, PAgP, and static EtherChannel configurations, including how active, passive, desirable, and auto negotiation modes affect whether an aggregated link is established.
Link Aggregation Protocols
802.3ad originally defined link aggregation, and so this was the original set of instructions on how these link aggregations was going to happen, how it was going to be implemented.
And as tradition holds, Cisco decided they wanted their own version, so they came up with EtherChannels. They call it EtherChannels. The industry standard out there is IEEE 802.3ad, so this is what other vendors will use. Some other vendors have their own versions of it as well. Cisco has EtherChannels and has implemented EtherChannels, so essentially it's their version of 802.3ad.
What the IEEE wanted to do is they wanted to create an automatic version of this, something that would auto configure, and so they came up with IEEE 802.1ax. Essentially it still uses this IEEE 802.3ad, but this is the automatic configuration or the auto configuration of it. So it is the link aggregation control protocol, or LACP, and it can set up these link aggregations automatically.
Cisco wanted their own version of this, of course, so they came up with port aggregation protocol, or PAgP. So this is their Cisco proprietary, and it's an alternate to LACP.
One thing to note is that to create EtherChannels, we could either just turn on EtherChannel and have it functioning, or we can set it up to be a LACP connection where it auto creates these links, or we could set it up to be a PAgP, so then we have this port aggregation protocol functioning and setting it up automatically. So we can choose the Cisco version of auto creation of these, we can choose the industry standard or the non-proprietary version of this, or just turn it on and say this is going to be EtherChannel, let's turn it on.
With the Cisco curriculum, with taking the Cisco test, from here on out, rather than calling it link aggregation, let's call it EtherChannels, because that's Cisco's version of this.
Essentially an EtherChannel can be at one of three states. We can turn an EtherChannel on, or we can use LACP, or we could use PAgP. I actually added the off just by not having the command on here altogether.
And then there's also, if we choose LACP, we can either set it to be active, where it is actively trying to be an EtherChannel, it's actively trying to be a link aggregation, or we can set it into passive mode, that says I'll be it if the other side wants to be it.
PAgP has similar settings to it, although they name them a little differently. It's desirable, that I desire to set up a link aggregation, I desire to set up an EtherChannel, or it's auto, well, I'll do it only if the other side wants to do it.
What we're going to be doing is we're going to set up EtherChannels on both switches, but there are some different configurations that we can have, and depending on what configuration we have will depend on what it sets up.
Let's say across the top here we have switch one, and across the left side here we have switch two. Let's say switch 2 is set for EtherChannels to be on, and switch one EtherChannels is to be set on: then yes, we create an aggregation, we create a binding, we've bonded these channels together.
But if we have switch one on and then we try to use LACP, it's not going to create it, because one side's trying to automatically create a link while the other side just says, well, I'm on. That's not going to work out, so that's where we see these nodes are not going to be created here.
If both of them are set to active, they're actively trying to say, hey, let's set up this link, let's aggregate these together, let's bind these together, let's get this EtherChannel going, and so obviously it'll create that. If one of them is in passive mode and the other in active, it'll still create it. But if they're both in passive, they're both saying I'll do it if you do it, I'll do it if you do it, then it doesn't happen, and that's where we see the no.
PAgP is the same way, and it has all the same settings to it, except that we just name it differently: desirable and auto. So I'm not going to cover this rule in depth, because it's pretty much the same settings here.
Link aggregation protocols, as I mentioned, are fairly simplistic. There's not a lot to it. There actually is quite a bit more of nuances to how you can distribute the traffic going across here, so there is quite a bit more to learn with this, but for this course we don't need to know all of that. This is pretty much the information you need to know to pass the CCNA exam.
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