ASUS USB-C2500 2.5GbE USB 3 Adapter Review

Today we are going to take a look at the ASUS USB-C2500. This is a fairly simple USB 3 to 2.5GbE adapter. Practically, it lets you get 2.5GbE speeds, or speeds thereabout, by using a USB port. This can be very important with smaller systems as we have seen with our Project TinyMiniMicro series where there are limited expansion options. Many of these adapters come from smaller brands, but this one comes from ASUS making it intriguing.

In the first half of 2021, we did a USB 3 to 2.5GbE adapter review series. The last one was the UGREEN USB Type-C to 2.5GbE review. Since we are using these more often, it is time to revisit the topic. We are going to be doing this series over the next few weeks and it will culminate in a buyer’s guide similar to the USB 3.1 Gen1 to 5GbE Network Adapter Guide. With 5Gbps USB 3.1/3.2 Gen1 ports becoming very common, this is a good way to add inexpensive 2.5GbE.

ASUS USB-C2500 2.5GbE USB 3 Adapter Overview

The main body of the USB-C2500 is metal, but it is not entirely metal since both sides of the main box utilize plastic faceplates. Some 2.5GbE adapters like the Plugable 2.5GbE USB-C and USB NIC are plastic. We will quickly note that this is not as heavy as the Sabrent NT-S25G.

On one end of the dongle there is an RJ45 port with two small holes for LEDs. Something we noticed is that this NIC sheds less light out at angles for port status than some other units where the LEDs extend to the edge of the case. If you still want status lights, but you do not want the status LEDs to be flashlights, this is a nice feature.

ASUS utilizes a USB 3.1 Gen1 Type-A (thank you again USB naming convention folks) connection. Some units we have seen have adapters to allow the NICs to operate as either Type-A or Type-C ports. We wish ASUS used a solution for that rather than having a fixed port.

The cable is a nice braided cable, but it is also very short. The cable is just long enough to clear the port area. When installed, the box part starts around 3″ or about 7.6cm from a USB port’s face. Some prefer longer cables, others like smaller cables since there will already be an Ethernet cable sticking out of the other end.

Something that is a bit different is that we see a normal set of regulatory markings. Many of these adapters come from small vendors that have few markings on them, so this is different. We have another unit that has no markings on the chassis. This is an ASUS unit, so it is what we would expect from a big company.

On that front, the majority of units we get come in some small cardboard boxes where there is simply an adapter. Since this is ASUS we get four pamphlets with a warranty, a manual, and other notices. The difference was stark enough to warrant a photo.

Overall, these are very simple devices. One item we wish is that ASUS simply publicly stated it uses the Realtek controller, but we found that information immediately upon plugging the units in.

ASUS USB-C2500 2.5GbE USB 3 Adapter NIC Setup

In Windows 10, the adapter was dead simple to set up, most of the time. You plug in the adapter, and it connects with a DHCP address. It identifies as a Realtek 2.5GbE NIC and everything works. We had a different experience here. Instead of an autoconfiguration, we were presented with a drive that had a Realtek driver.

Our advice, and more on this in the performance section, is to download the Realtek driver (link here) directly from Realtek. The company has added a Captcha for downloads and that is just a pain. Here you will see the Captcha is 5+7 but you put the answer in the box rather than typing “5 + 7”. That seems obvious to some, but it could clearly use a prompt even if it says “Result of the math operation above:”

Once this is done, the adapter, or in this case, adapters, are identified. Many simply say Realtek 2.5GbE, but these show up as “ASUS 2.5G Ethernet USB Adapter” in Windows.

Once that is complete, you have an adapter. These are set to a private network, but one can see the auto negotiated 2.5Gbps speeds.

That driver and setup is important because it directly impacted the NIC’s performance.

ASUS USB-C2500 2.5GbE USB 3 Adapter Performance

We tested the unit in Windows 10, Windows 11, and macOS (Linux will be coming as this series progresses.) Still, since we started this series with Windows 10, we are sticking to that here. We tested Windows 10 PCs going from the ASUS USB-C2500 2.5GbE USB 3 NIC to a TEG-25GECTX NIC. We also pushed these through a multi-gigabit switch and saw the same results within our normal 0.7% margin of error on both setups.

Here is the performance on the older Realtek driver from 2020 that came on the device:

Something you will see is that the device ran into big errors, then dropped completely. It actually reset and was re-initialized by the system.

For comparison, we tried the newer December 2021 driver and saw consistent performance:

Clearly, we are getting better than 1Gbps speeds at closer to 2.3Gbps measured by iperf3. One will also notice better performance on the new driver versus the old one when it was not dropping.

These NICs all generally perform about the same, so our advice is to get new drivers whenever utilizing Realtek NICs, and this goes beyond just these 2.5GbE USB adapters. All of these adapters run relatively cool. It is the 5GbE variants that tend to have heat issues.

ASUS USB-C2500 2.5GbE USB 3 Adapter Power Consumption

ASUS did not list power consumption for its NIC. We tested the ASUS 2.5GbE PCIe NIC both in a direct attach 2.5Gbps connection using CAT5e near the edge of the 100-meter maximum run length. We also tested the solution on a short connection to the switch using CAT6. We measured the impact on an Intel Atom C3558 server because that platform has relatively stable clock speeds and a low platform power base so we could see the impact measured at the wall.

• ASUS USB-C2500 to TEG-25GECTX 300 feet / 91.44 meters: 1.8W
• ASUS USB-C2500 to Switch 10 feet / 3.05 meters: 1.2W

These are very low numbers, and should not dissuade from updating to a faster 2.5GbE standard. All of the units we are testing are in the 1.7-1.9W and 1.2-1.3W ranges respectively to the point that we are considering removing this section since it is so repetitive. Under 2W is a margin of error for higher-end systems. For lower-end systems it is noticeable but likely has little to no impact. If you are upgrading from 1GbE to 2.5GbE for network performance, then this is a very minor power increase.

Final Words

This is certainly far from the only solution on the market. We generally see these ASUS adapters in the $29-30 range (we will have a targeted Amazon Affiliate link price puller above.) Most of these 2.5GbE to USB 3 adapters are in the $17-40 range, putting ASUS directly in the pack. The driver situation was about what we see with others as well. Almost all of these adapters are Realtek RTL8156 / RTL8156B based. As time goes on, more are RTL8156B NICs as it seems the revision has taken over. We have even seen some originally RTL8156 NICs ship with RTL8156B’s recently, so our sense is that this will be homogenized over the next few quarters if it is not already.

With ASUS, we get a nice metal case and a braided cable which are pluses. Sabrent has a sturdier chassis, but it is much heavier. One item we would really have liked to have seen was a dual Type-A and Type-C solution. On the other hand, Type-A ports are more plentiful and if you need Type-A for a system to be a fixed NIC, then that is fine. If you have one of these laying around a rack, just to plug in with a laptop, then perhaps you will prefer having a dual solution. Others will just want Type-A and prefer a branded solution like this ASUS.

Overall, this is a good solution. While the market for these is rather undifferentiated, the ASUS brand shows in simple things like actually having regulatory notices and also picking a few physical attributes that cost slightly more but add to quality. At $50 this would be hard to recommend. At $20, it would easily be a top option. At $30 it is a solid but not stand-out offering.