Why Am I Not Getting My Full Internet Speed on Fiber?

Despite the fact that fiber is amazingly fast, it’s not necessarily delivering the speed it promises to at least a few people. Everyone loves having a fast connection, but an even faster one beats everything else! The moment you get a 100 Mbps downstream connection, you want to quickly test the line to see how fast you can download enormous files. It’s in that moment that you might come to the realization that your 100 Mbps line isn’t giving you all that much speed. At that point, it’s time to look through this guide to see what’s wrong!

Are you sure you’re using the right measurement?

Remember that megabyte and megabit are used to describe two different measurements of data. The data transfer speed on your network is usually measured in megabits per second. That’s one-eighth of a megabyte per second.

That means that if you’re running on a 100 Mbit connection, your download speed should be roughly 12.5 (100/8) megabytes per second at maximum.

Testing Your Speed

Before reading onward, you should test your internet speed. You can do this through various speed testing utilities online, such as Speedtest.net.

1: You’re using a router.


Most consumer-level routers are absolutely lousy at transferring data at rates higher than roughly 10 to 14 megabits per second. That’s because their internal hardware is very slow and can’t process all of the signals coming in at one time. The problem is further exacerbated when more devices are connected to the router, or when you’re downloading from many sources at the same time (like you would with a torrent).

To test whether the router is causing you problems, try connecting your Ethernet cable directly to a relatively fast computer, if possible. Just be aware that hardware limitations on the computer, including the quality of the network card, could also cause problems! If your computer’s hard drive isn’t fast enough to record all the information coming to it, your network card will make no further queries to it. You end up with an overloaded drive and a bottlenecked connection.

2: You may have internet speeds restricted at an international level.


Various countries restrict the speed of web data crossing their borders (in or out) to avoid bottlenecking the country’s infrastructure. For example, Romania Data Systems (RDS) – one of the biggest Internet service providers (ISPs) in the country – advertised 100 Mbit connections for its customers but restricted international speeds to roughly one-tenth of this in the past. It’s possible that many Internet service providers do this, but I’m not sure exactly how many.

To find out whether you’re affected by this, call your Internet service provider and ask them if you’re being restricted on an international level. They should reply with a clear “yes” or “no”. Don’t forget to be a little assertive.

3: International peering may be at fault.


Are you in Germany downloading something from Malaysia? Is a torrent of yours full of foreign seeders? Answering “yes” to either of these questions may provide the key to finding out whether you’re experiencing peering issues. For one ISP to transfer data to another ISP, the data must first pass an Internet exchange point (IX or IXP). Similar rules apply to transfers being made across oceans or large terrestrial distances. When an IX is clogged, it may result in a slow-down for everyone trying to transfer data outside their ISPs’ networks.

If your speed is very high at some hours, but very low at others, you might be experiencing the Internet’s version of rush hour.

4: Your ISP’s hardware can’t handle those speeds.

While fiber optic cable can transfer at some immense rates, ISPs don’t always upgrade their hardware accordingly. They might be using newer routers, or they may have opted to go the cheap route and just retrofit whatever hardware they can while trying to keep a balance on their budgets. This rarely happens, though. But keep in mind that for the first time in a very long while, even the most state-of-the-art ISP hardware can’t keep up with the optimal speed of fiber optic cables!


As you may have gathered from here, it’s very difficult to properly pinpoint exactly what is causing a slow-down in your system. You’ll have to perform lots of trial-and-error verification, but eventually you may find the culprit. If you have any questions about this subject, be sure to leave a comment below so that others can assist you!

Miguel Leiva-Gomez Miguel Leiva-Gomez

Miguel has been a business growth and technology expert for more than a decade and has written software for even longer. From his little castle in Romania, he presents cold and analytical perspectives to things that affect the tech world.


  1. Another reason may be that your ISP is throtling the fiber speed, hoping to induce the customers to “upgrade” to a faster, more expensive plan.

    1. Surprisingly enough, countries with lower corporate tax rates suffer much less from internet speed throttling than others. I think it has more to do with their willingness to reinvest their revenues in infrastructure. When they see a predictable economy with less impediment, they are more likely to act upon their desires to upgrade their own equipment.

      Despite the fact that fiber can theoretically deliver multi-TB-per-second speeds, the packet transfer and routing equipment limits this by a factor of at least ten. Routers aren’t as straightforward as the cables connected to them. They have to process packets and take the path of least resistance. This involves several calculations just for one user. Since they have limited processing power, one single ISP router might be able to top about 15 Gbits per second (sometimes much less, as is the case with some of Romania’s ISPs).

      Governments forcing ISPs to record packet transfers adds to the hardware burden of the company, making speeds suffer even more. The most powerful incentive for higher speed between the two is actually that of the ISP, which would rather not make service speeds to their customers fluctuate for the sake of recording something they may have typed into an address bar.

  2. Yep it’s unfortunate that in Australia, where we’re gradually rolling out broadband internet (instead of ADSL), it seems that most retail plans (a) are asymmetrical, because the ISPs will be able to get away with that for a while because people are used to it, and (b) involve a range of different speeds, which means that the user decides how much braking is put on the connection by the ISP.

    I don’t even know if any of the ISPs will sell plans where speed is not throttled.

    1. Australia suffers from a weird situation and bad management from the international end of the IXPs. International exchanges leading out of Australia are shoddy at best and must be upgraded significantly to support the upstream bandwidth demands of the country in general. I’d give it at least a few years until they have the ability to offer the whole country a 100/100 bandwidth package.

  3. You left out something important. Even though you have fiber to your house, it is slowed down because you have Copper wires throughout the house to your computers.

  4. A local customer of mine who bought brand new CAT5e or CAT6 cables, could only get 40Mbps out of his connection trying multiple cables, which should have been a 100/100Mbps. One of our techs just to check, made a new cable and tested it and got 98Mbps/97Mbps on what should be a 100/100Mbps fiber connection. They tested a new packaged cable and again, 40Mbps was the max he could get. So don’t rule out bad cabling. We have fiber to the home and 99% of the time will get better than advertised but we do run in to crappy routers like DLink and then bad cables. Just FYI.

    1. I’ve been in that neck of the woods before. Is it possible that your customer may have had EM interference? Although from what I understood in your message, you did achieve a 98/97 Mbps throughput. Were you trying to run the cabling through a different area? Because that looks like an EM issue if so.

      I don’t mean to sound overly annoying and redundant, but did you check hard drive load? When the HDD’s overworked, network packets sit silently in the queue waiting for it to free up again, impacting speed.

      Thanks for your contribution to this discussion! It’s very helpful!

  5. This particular setup was in a room in an underground garage. The run was about 15 feet from router to ONT. The drops were the same and tested on multiple laptops. The result was virtually identical on both. Never over 40Mb. It was weird. I suspected that it was marked as CAT5 but was really something equivalent to a CAT3. The twist could have been off, who knows. They had been getting an average of 80/80 but a new vendor wanted to update the wiring so they ordered all new jumpers. After we added the home made cable, each device got similar results around 98/97. So, I am convinced it was a cable issue.

    1. Bad wiring? I’m not sure what it could have been, but I’m glad you resolved the issue. Cabling is bound to be off at the crimping point on some cables. I’ve heard of those problems before, but never experienced them myself.

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