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DEMO: Configuring EtherChannels

EtherChannel configuration on Cisco switches covers how to bundle multiple physical interfaces into a single logical port channel using the channel-group command and supported negotiation modes including static, LACP, and PAgP.

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About this video

EtherChannel is a link aggregation technology that bundles multiple physical Ethernet interfaces on a Cisco switch into a single logical connection, effectively multiplying available bandwidth and providing a level of redundancy between interconnected switches. Rather than treating each physical link independently, the switch presents the bundled group as one interface, simplifying traffic management and making fuller use of available cabling between devices. Configuration requires assigning the relevant physical interfaces to a channel group using the interface range and channel-group commands, specifying both a group ID and an operational mode. Available modes include static on, which establishes the EtherChannel without negotiation, as well as LACP active and passive modes and PAgP desirable and auto modes, which allow the switches on either end to negotiate channel formation automatically. The channel-group command applied to the physical interfaces automatically creates a corresponding logical port-channel interface on the switch. Once the port-channel interface exists, all trunk, access VLAN, and other interface-level settings should be applied there rather than directly to the individual member ports. Configuring at the port-channel level ensures that settings are consistent across every physical link in the bundle and reflects industry best practice for EtherChannel management. The physical member interfaces inherit the configuration from the port-channel, keeping the setup clean and reducing the risk of mismatched settings causing the channel to fail. Several show commands support verification and troubleshooting, including show etherchannel summary, which provides a concise view of configured channels and their member ports, show interfaces port-channel, which displays traffic statistics and interface status, and show running-config, which confirms the configuration applied to both the logical and physical interfaces. These tools allow administrators to quickly confirm that the EtherChannel is properly formed and operating as expected.

What you'll learn

What's covered

EtherChannel Configuration

Aligned to

Cisco CCNA
2.4 Configure and verify Layer 2/Layer 3 EtherChannel (LACP)

Key terms

EtherChannel
Cisco's implementation of link aggregation that bonds multiple physical links into a single logical channel to increase bandwidth and redundancy.
channel-group
The Cisco IOS command used on individual switch interfaces to assign them to an EtherChannel group and specify the negotiation mode.
Port Channel
The logical interface automatically created on a Cisco switch when physical interfaces are assigned to a channel group, used to apply shared configuration settings.
Link Aggregation Control Protocol
LACP
An IEEE 802.3ad protocol that automatically negotiates and manages the bundling of multiple physical Ethernet links into a single logical link aggregation group. LACP enables dynamic detection of compatible links and provides failover if individual member links go down.
Port Aggregation Protocol
PAgP
Cisco's proprietary link aggregation negotiation protocol that automatically creates EtherChannels using desirable or auto modes.
Bandwidth
The maximum rate of data transfer across a network path, typically measured in bits per second.
Redundancy
The duplication of critical components or systems to increase reliability and availability.

Topics

Etherchannel Cisco Switching Lacp Pagp Port Channel Link Aggregation Networking

Transcript

I am on switch one. Let's take a look at some of the configurations to configure EtherChannels.

First of all, I'm going to just show you two of the interfaces I'm going to configure. I'm going to show run interface fa 1 0 4, which is one of them, and there's no configuration on this port at this point in time. Same thing with five: there's no configurations on here.

Configuring the Channel Group

So let's get in here and let's start configuring it. I'm going to get into the global configuration mode and then we will configure both of these ports. I can do one at a time, and they don't need to be next to each other, but it's just easier for me to do this as a range. So, interface range fa 1 0 4 to 5, and we'll configure them both.

I'm going to do a channel group and then a channel group ID, so I'm just going to call this one channel group one. I just need to have an ID for this channel group. And then I'm going to type in mode, and let's do a question mark.

The different modes I can do on this: I can just turn it on, so that's just the straight EtherChannel, I can create an EtherChannel with this. Or I can automatically create these with the other side by turning it on to using LACP, either passive or active. Active actively tries to create an EtherChannel group, versus passive will if the other side wants to. Or PAgP, with desirable or auto.

So I have a few choices here. For most of my networks I just turned them on and just not had this auto-negotiate anything, just create it. So I'm going to type in on, I'll hit enter, and it says creating a port channel interface, Port channel one.

One thing that I always found a little interesting is that I call this a channel group one and then it creates a port channel one. So just realize there's a difference there. The channel group is the command that you enter on the individual interfaces, but the port channel is the interface that it then creates.

Let's just take a look at what we have. We'll do a "do show run interface fa 1 0 4". Let's take a look at one zero four, and we can see that there's only one command that's on here at this point in time.

Configuring the Port Channel

So I'm going to exit out of the interfaces; I'm done configuring it there. I could go into that interface and configure zero four now and configure zero five, but the problem with that is then those configurations can be off. So best practices in this case right here is to then get into that port channel and configure the port channel.

I'm going to get into the interface port channel, and it's Port channel one. So I'm inside that interface, and then I would configure this port channel the way I want to configure it. I have the commands here. It doesn't matter how you're going to configure this, whether it's going to be access or trunk or however you're going to want to configure it. For this particular one I want to configure it as a trunk line, and so I've got my commands.

And now, the port channel. I can do a show interface, or I'll do a "do show run interface port channel one". So I'm going to take a look at the running config of this port channel one, and the commands I just copied and pasted in there are in there, which makes sense. But the only thing I want to show and notice here is that it actually enters the information on this as well, with the exception of the description. The rest of it is entered on here; these three commands are entered onto this interface. So now it's acting as a channel group and as an EtherChannel.

Show Commands

What are a few other commands when I'm going to take a look at things? Of course show run is one of those that is always great to see what is happening on my switch, and I will show you that the port channel shows right at the top, right before the rest of the physical interfaces are on here. So we see that port channel right there. So that's interesting. And then we can scroll down and we see zero four and zero five with the configurations that we just established on there.

I can do port channel, we'll take a look at Port channel one, and just like I can do a show interfaces on my other interfaces and see some stats and stuff involved with that, I can see that with this one as well.

I can do a show etherchannel summary and see a summary of the port channel that's on here. And then I can also do a show etherchannel and see some information on there as well. So there's a few show commands I can use to do some troubleshooting and see what's going on with this, and take a look at what's going on on my interfaces.

So there you have it. Fairly simple, really, to set this up. All there was was really a command to set up EtherChannels on the two ports, and that's the channel group command, and then I go into that interface that it creates, that port channel that it creates, and configure the port channel, and then it's set up. It's as simple as that.

So they're pretty cool. I like setting these up. I like to set up multiple links. I've had switches that have had four or eight connections between the switches, and then you can get more bandwidth out of this. So I think it's a great thing.

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