Are Ethernet Cables Backwards Compatible?

Ethernet Cables Backwards Compatible title page

Are you looking to replace ethernet cables in your home network?

If so, you’ll probably need to answer some important questions before making any decisions.

You’ll need to know:

In addition to the information above, you’ll need to determine if the cables you want to buy are backwards compatible with the ones you’re replacing.

I know, this can feel overwhelming.

So let’s start at a high level: are ethernet cables backwards compatible?

The good news is that most ethernet cables commonly used today (cat5e, cat6, cat6a, and cat8) are backwards compatible with each other. The exception to this is cat7 cables.

In this post, I’ll go into detail about why these cables are backwards compatible. I’ll also talk about why you’ll want to avoid using cat7 cables in your network.

How to tell if an ethernet cable is backwards compatible

When it comes to identifying the ethernet cables that are backwards compatible, there’s one basic specification to pay attention to.

The specification that we care about the most has to do with the connectors at the ends of the cable.

To be specific, I’m talking about these:

Ethernet cable RJ45 connector

The picture above is an RJ45 connector.

RJ45 is an ethernet cable standard that describes how an ethernet cable terminates at each end. In other words, it identifies the type of connector at each end of ethernet cables.

The “RJ” stands for “registered jack”, and the “45” is just an identifier for the interface standard of the connector. Essentially, the purpose of the RJ45 connector standard is to provide a way for everyone to make cables the same way.

On the other side of the coin, it makes it easy for companies making computers, gaming systems, and other devices to make their devices compatible with the standard. All they have to do is add a port on their device that fits the RJ45 standard.

That’s why you’ll find RJ45 ports on most of your electronic devices. For example, my router has 4 ethernet ports on the back of it that are for RJ45 connectors.

Ethernet ports on router

The RJ45 standard is universal. Everyone uses it.

Well, almost everyone. Unfortunately, not every ethernet cable adopted the RJ45 standard.

To bring this all together, the cables that are backwards compatible with each other will all be made to the same RJ45 connector standard.

So which ethernet cables have connectors made to this standard?

I’m glad I asked.

Which cables use RJ45 connectors?

Ok, so we’ve determined that the cables that are backwards compatible will have RJ45 connectors.

The good news here is that most ethernet cables used today are made to that standard of connector.

To be specific, the following categories of cables have RJ45 connectors on them:

  • Category 5e
  • Category 6
  • Category 6A
  • Category 8

So what does this mean, exactly?

It means you can replace any of the above cables with a different category of cable without any issues, so long as the cable you’re replacing it with is also in the list above. For example, you’ll have no problem replacing a cat5e cable with a cat6A cable.

Although the cables listed above are most of the ethernet cables you’ll see today, it’s important to note that not all categories of ethernet cables are compatible with each other. As you’ll find more about later, category 7 cables aren’t compatible with the cables listed above.

You may be wondering if categories 1 through 4 of ethernet cables are backwards compatible. To be honest, I left them off the list above because you won’t see them used today.

They don’t support speeds fast enough to keep up with the demands of today’s networks. It’s sad, but the truth is they’ve been left behind at this stage of the game.

What makes ethernet cables backwards compatible?

Ok, so ethernet cable categories 5e, 6, 6A, and 8 are all interchangeable with each other.

We also know that the reason they’re compatible with each other is because they all have RJ45 connectors.

This only tells a part of the story, however. To find out exactly why these cables are compatible, we have to dig a layer deeper.

That’s right, I’m talking about the wires inside the cables.

Ethernet cable wiring

Let’s start with the basics here.

Inside an ethernet cable, you’ll find 8 copper wires. This is what it looks like inside one of your ethernet cables:

8 wires inside ethernet cable
There are 4 pairs of twisted wires inside most ethernet cables

These 8 wires are used to transfer information through the cable.

How they do that isn’t super important for this discussion, so we’ll blast past that part.

What’s important is that each of these 8 wires inside the ethernet cable has a job to do.

Some wires are used to transfer data to the other side of the cable. Other wires are meant to receive incoming data from the other side.

You might be shocked to find out that some of these wires inside an ethernet cable aren’t used at all.

So now for the hard hitting question: how do you know which wires are meant to send data and which wires are meant to receive data?

The answer to this question is similar to a sports team. Each position on the field has a certain job.

The same goes for ethernet cables.

The job of a particular wire is based upon the position of the wire inside the connector it’s attached to.

So who says what wire is responsible for what?

For this information, we have to go to another standard.

Let’s meet the TIA/EIA-568 standard.

The TIA/EIA-568 Standard

The TIA/EIA-568 standard plays an important role in how ethernet cables are wired.

In short, it provides a few different requirements that ensure ethernet cables are all made the same way. For this discussion, the area we’re focused on has to do with the wiring of cables.

Going back to our sports analogy, if the wires inside the ethernet cable are the players on the field, the TIA/EIA-568 standard is the rulebook for the game.

TIA/EIA-568 details what order the cables should be in inside the RJ45 connector to ensure all cables are made the same way.

In other words, it defines the positions of the players (copper wires) and where they should stand on the field (RJ45 connector).

So how does this apply to ethernet cables?

To answer this, we need to refer back to the RJ45 connectors at the end of ethernet cables.

Inside the connectors, there are 8 channels that the wires inside the ethernet cable fit in to.

Ethernet cable wires inside RJ45 connector

As you can see, the colored wires are laid out side-by-side in the channels of the RJ45 connector. What the TIA/EIA-568 standard does is it defines which wire should be in which channel.

What’s interesting is that there are two different ways that these wires can be laid out inside the RJ45 connector. These are called ethernet cable pinout configurations.

As long as the wires inside the RJ45 connector follow one of these standard pinout configurations, the ethernet cable will work properly. It doesn’t matter which one is chosen.

Why are these standards important for backwards compatibility?

Now that we’ve laid this all out, we can get to answering our question.

How do the RJ45 and TIA/EIA standards allow these ethernet cables to be interchangeable?

In order for ethernet cables to be interchangeable, two things need to be in place. The cables need to:

  • Be wired the same way
  • Have the same connector

These two standards take care of both of those requirements. The RJ45 standard will make sure all the cables have the same connector and fit into the same devices. The TIA/EIA standard will ensure that wires inside the cables will be in the same order.

To put it another way, if two different cables meet both of the above requirements, the only thing different about them will be the speeds they support. They’ll support different speeds because of the different wires that’re used inside the cable. It has nothing to do with the connector on them or the configuration of the wires inside the cable.

This is why different categories of ethernet cables support different speeds. The wires inside the cables are made to different specifications. The different specifications determine the maximum speed the cable can support.

The good news is, if you need to get an ethernet cable that supports a faster speed, it’ll be interchangeable as long as it’s a category 5e, 6, 6A, or 8 cable.

Do yourself a favor and make sure you’re using one of these categories of cable in your network.

Which ethernet cables are not backwards compatible?

If category 5e, 6, 6A, and 8 cables are all interchangeable, which cables aren’t?

There’s only one type of modern-day cable that isn’t. Category 7 cables.

Some of the earlier versions of ethernet cables aren’t backwards compatible either, but you won’t see them in use today.

To understand why cat 7 cables aren’t compatible with the other categories, let’s revisit the criteria we posed before. In order to be compatible with each other, cables need to:

  • Be wired the same way
  • Have the same connector

Let’s address these criteria individually.

Ethernet cable compatibility chart

Are cat 7 cables wired the same way as category 5e, 6, 6A, and 8 cables?

This is a definitive yes.

Cat 7 cables are wired exactly the same way as the other common categories of cables. Cat 7 cables will be wired in one of the two approved configurations detailed by the TIA/EIA standard.

Ok, so we can check the box of the first criteria that compatible cables need to meet.

On to the next one.

Do cat 7 cables have the same connectors as category 5e, 6, 6A, and 8 cables?

This is where things fall apart.

Category 7 cables don’t utilize the RJ45 standard for connectors. They use a different standard called GG45, which stands for GigaGate 45 or ARJ45, which stands for Augmented RJ45. They can also be outfitted with TERA connectors as well.

Of course, the issue here with category 7 cable connectors is that they’re not interchangeable with the other commonly used categories of cables.

On top of that, you won’t find any GG45/ARJ45 or TERA ports on any of your computers or internet devices.

As a result, you won’t see these cables used very much.

With that said, it’s possible to outfit a category 7 cable with an RJ45 connector, but there’s little benefit to this. If you outfit a category 7 cable with an RJ45 connector, it’ll have the same performance characteristics as a category 6 cable.

In fact, if you try to buy a cat 7 cable online, you probably won’t find any with a GG45/ARJ45 or TERA connector. They’ll all have RJ45 connectors on them.

Don’t fall for this. These cables are either fake, or they’ll perform just like a cat6 cable. You’re better off just buying cat6 cable instead.

In conclusion, this is the reason why cat 7 cables are incompatible with cat 5e, cat 6, cat 6a, and cat 8 cables. They don’t utilize the same connector standard.

Wrap up

Well, there you have it.

That’s a complete breakdown of which ethernet cable categories are compatible with each other.

Chances are, the cables you have in your home all have RJ45 connectors, so you shouldn’t have any issues if you ever want to upgrade or replace them. You probably wouldn’t be able to get a cat 7 cable with a GG45/ARJ45 or TERA connector even if you tried.

If you have any questions about this information, or you’d like to share you experiences with your ethernet cables, please drop a line below.

If you’re interested in reading some more about similar topics, check out these posts that I’ve written:

Do the Colors of Ethernet Cables Matter?

How Long Do Ethernet Cables Last?

Are Ethernet and Phone Cables the Same?

How Do You Crimp Ethernet Cables?

What Does Cat Mean for Ethernet Cables?

Ross Ricky

Ross Ricky is an engineer and cybersecurity professional who wants nothing more than for you to get the most out of your home network.

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