Technology / Networking

How to Deploy LACP Between IOS and Junos

by Jon Welling
How to Deploy LACP Between IOS and Junos picture: A
Published on April 28, 2022

How can you create faster network connections that are also more resilient with higher availability without spending additional money? You could use LACP.

LACP is an industry-standard way to combine multiple network connections together to create a single faster logical network connection with the benefit of redundancy. Though there are numerous proprietary ways to do this, LACP is available on just about every switch. Best of all, it works the same way.

It's common for businesses to use switches from multiple vendors, though. Two of the most popular networking switch vendors are Cisco and Juniper. So, today we are going to walk through how to deploy LACP between IOS and Junos.

What is LACP?

LACP stands for Link Aggregation Control Protocol. It is part of the IEEE 802.3ad specification. LACP is a standard method for combining multiple physical links in a switch into one logical link. By combining physical links, two switches can increase bandwidth, increase receive and transmission rates, load balance connections, and create higher available connections.

What does all of that even mean?

Back in the days of dial-up internet, it was every geek's dream to be able to use multiple internet connections to make downloading music and playing games faster. Back in those days, we didn't have the blazing fast 300+ Mb ISP connections that we have today. Back then, we had a 56Kbps connection that used analog signals traversing over a standard telephone line to transmit data.

Most households were limited by that single 56k connection. Each dial-up internet connection required its own phone line. Most homes only had one phone line due to costs.

Some privileged households had multiple phone lines with different phone numbers, though. Families that could afford multiple phone lines usually paid that extra expense so everyone in the house could both surf the internet and talk on the phone. Because dial-up connections send analog signals through the phone line, you couldn't talk on the phone and surf the internet simultaneously. In fact, picking up a phone while a computer was connected to your ISP would often disconnect that internet connection.

What if you could use both phone lines for two different internet connections and combine them into one?

That's what 'shot gunning' modems were. Special modems were created that could combine two internet connections on different phone lines into one logical internet connection. That doubled the speed from 56K to 112K (almost as fast as the first residential DSL lines). It also made the internet connection more stable. If one connection was lost, the modem would simply connect it again. Thus, the person using the internet would only experience a brief moment when internet speeds dipped.

This is a very long analogy of what LACP is. Instead of combining multiple telephone connections, LACP combines various network connections together.

There are a variety of protocols that do the same thing as LACP. The important thing about LACP is that it is an IEEE standard. Likewise, many network equipment vendors implement LACP faithfully to spec. That means it's not difficult to deploy LACP between different switch OSes like IOS and Junos.

How to Deploy LACP Between IOS and Junos?

LACP is a valuable way to combine multiple network interfaces together to act as one logical interface. For example, that means you can connect three 1Gb connections together to create a 'single' 3Gb link instead.

LACP also has failover strategies built-in. For example, if one of those three interfaces goes down, you still have a 2Gb connection. That means data is still flowing through your network, albeit not as fast.

It's common for organizations to have networking equipment from different vendors. In addition, network switch soup becomes more common as businesses start acquiring or merging with other companies. So, let's look at how to configure LACP in both IOS and Junos.

How to Configure LACP in Cisco IOS

Configuring LACP in Cisco IOS is easy. The steps below are the specific commands you need to enter in the command-line environment while remotely connected to your Cisco equipment. We are assuming that you are using a newer version of IOS for these commands.

  1. Interface range gigabitEthernet 1/0/7-8

  2. Channel-group 1 mode active

  3. Int por1

  4. Switchport mode trunk

  5. End

Now, let's walk through what each of these commands does.

In step one, we are selecting a group of interface ports in the switch. In this case, we are selecting port 7 and port 8. You can use as many or as few ports as you would like, but make sure those ports also connect to the corresponding switch with which you are creating an LACP connection.

Next, we are defining a channel group and setting that group to active. In the instructions above, we designated it '1'. This may be different for your environment. This will create a port1 group.

In steps 3 and 4, we enter configuration mode for port1 and set the mode of that group to 'trunk.'

Finally, we exit the configuration interface.

That's how you configure LACP for IOS devices.

An Overview of How to Deploy LACP Between IOS and Junos [Video]

In this video, Knox Hutchinson covers LACP: an open, standard protocol also known as 802.3ad that’s essential for load balancing and fault tolerance. For networks supported by one hardware vendor, implementing LACP is pretty straightforward. But for networks that don’t work exclusively with one vendor like Cisco or Juniper, deploying LACP and link-aggregation between switches can be tricky. Watch as Knox explains deploying LACP between IOS and Junos.

How to Configure LACP in Juniper Junos OS

Let's walk through how to configure LACP on Junos devices. Junos devices need a few more configuration steps than Cisco devices, but the process is relatively similar. The commands below will be used to create your LACP enabled group of interfaces. Pay attention to steps 2 through 5, though. Notice that they appear to be repeated. We'll discuss that more below.

  1. Set chassis aggregated-devices ethernet device-count 1

  2. Set interfaces ge-0/0/2 ether-options 802.3ad ae0

  3. Delete interfaces ge-0/0/2.0

  4. Set interfaces ge-0/0/3 ether-options 802.3ad ae0

  5. Delete interfaces ge-0/0/3.0

  6. Set interfaces ae0 aggregated-ether-options lacp active

  7. Set interfaces ae0 unit 0 family ethernet-switching port-mode trunk

  8. Commit

  9. quit

Here's what those instructions do. First, after logging into Junos on your switch, you need to tell Junos how many chassis will have aggregated devices enabled. In this case, we are only concerned with a single switch (the one we are logged in to), so enter '1'.

Now we need to configure the interfaces. Unlike Cisco's IOS, you need to configure each port individually for Junos. This is the reason why steps 2 through 5 seem duplicated. In step 2, we are telling Junos to configure port 2 to work with LACP. Next, we delete the prior interface. Then we do the same thing for port 3 in steps 4 and 5. If you have any additional ports that you would like to belong to your LACP group, repeat those steps for each different port.

In step 6, we are enabling LACP. Just because we configured port 2 and port 3 to use LACP doesn't mean that LACP is active yet. We need to enable it first.

Finally, in step 7, we set the group of ports to trunk mode. Then we save the parameters and exit the configuration interface.

That's it. Though configuring Junos to use LACP does require more steps than IOS, the process is very similar. The most significant difference is that each port needs to be configured separately in Junos.

Wrapping Up

If you found this article helpful, you might be interested in taking an entire course for Juniper Link Aggregation.

LACP is a helpful industry-standard protocol for combining multiple switch ports together to act as a single port. This has the benefits of increasing bandwidth, applying load balancing between those ports, and creating failover connections between two switches.

It's common for businesses to have switches from multiple vendors. This is especially true for growing businesses as they acquire competitors. So, it may be necessary to configure LACP between different kinds of devices.

Thankfully, the process for this is typically the same. First, you need to select the ports you want to configure. Next, you need to combine those ports into a single group and enable LACP for that group. The process is typically that easy. Each vendor will have a couple of deviations for those steps. For instance, you can select all the ports you want to configure together in IOS. In contrast, in Junos each port needs to be configured separately.


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