Slow wired Ethernet speed on m1 MacBook Air using Belkin adapter

Try a different patch cable and preferably a previously-unused Cat 6 or better cable.

Check the Mac port settings: Use Gigabit Ethernet on Mac - Apple Support

Confirm the switch or router port is capable of Gigabit Ethernet (GbE) speeds.

If you’re connecting into a managed network switch, confirm that the port is set to auto-negotiate, or to GbE.

If the adapter still isn’t working at speed, swap it for another, and check with Belkin.

HELP! I've been having huge performance issues associated with an Belkin USB-C to Gigabit Ethernet Adapter.

Model number is hard to decipher but the numbers on the back are: R-R-K7S F2CU040, F2CU040, 8830ds22833 Rev.K00, 3423OL, HJKF2ZM/A and 45883 70160 under the UPC code sticker from Apple.

When I compare my speeds I get on my iMac which has a direct Ethernet port to the speeds I get using the Belkin adapter, there's a world of difference. The iMac is a consistent 933 down and 225 up (through Comcast). But the MacBook Pro connected to the Internet through an Ethernet cable going through the Belkin adapter, the speeds are all over the map, sometimes 140 down and 225 up, sometimes off, sometimes 922 down and 225 up, sometimes 113 down and 233 up, changing second to second (literally).

I tested this on 7 different MacBook Pro's both with Intel Chips and M1 chips with the same issue.

One post says that a 2.5GB dongle will solve but only 1 post says that.

Does anyone know anything about this and have an absolute answer? Thanks so much!

Looks to be this dongle: https://www.belkin.com/usb-c-to-gigabit-ethernet-adapter/P-F2CU040.html

Check with Belkin.

It would not be unexpected to have Wi-Fi outrun what you’re measuring with that dongle, and quite possibly also with Wi-Fi outrunning GbE on a semi-recent Mac mixed with decent-grade Wi-Fi gear with low interference.

As for some suggestions, scroll up and partake.

In addition to that, check the USB cable ratings too, as there are lots of cheap USB cables, and there are also some over-spec’d cables around.

Caveat: some vendors will have the same part number on different versions of the dongle, with very different parts. I don’t happen to know Belkin practices here, but several major vendors of my acquaintance will freely switch major components while preserving the same part salable part number. Put differently, characterizing the performance or behavior of the apparently-same part number may not be comparable or even applicable to a different implementation of that same part number.

StevenSulkin wrote:

I'm not comparing wifi with wired. All comparisons are wired. I'm not using a USB cable, I'm using a Belkin adapter as described above, the one from apple.

Yes, and Wi-Fi may well be faster than this particular effort.

Particularly at the speeds you’re reporting.

Various Wi-Fi 5 and Wi-Fi 6 connections are faster than GbE.

Solution: Simple, straightforward and absolute. Use a 2.5GB USB-C to Ethernet adapter rather than a 1GB and that will solve everything. Whether other people will have this problem if they are not configured like me, I don't know. But I sense many people are having this issue without even knowing it as they might not measure their speeds as often as I do, or it might not be that critical for them. My setup: My ISP is Comcast (cable) and their speed is 1000mbs down and 225mbs up. I have a Mac Book pro, Apple 1 Max and am on Sonoma 14.4.1. If I use a Belkin 1GB USB to Ethernet adapter (or other brands) the Internet speeds wildly change minute to minute and often doesn't exceed 175mbs down. When I changed to a 2.5 Belkin USB to Ethernet adapter all was solved. I tested back and forth many times and this solution is definitely correct for this problem. I tested on 6 other Mac Book pros with Intel chips and M1 chips and had the exact same result the 2.5 works, the 1 doesn't. I also tested my iMac which has a native Ethernet port built in and there was no issue coming from the same Comcast Ethernet cable. So the adapter is definitely the problem. Why? I don't know? Hardware or software mis-match of some sort I assume. Apple had no idea about this as I called Apple support and at least that person had no record of this problem, but said "he did hear some chatter" and I went into an Apple Store and no one heard of this issue (which doesn't mean the issues doesn't exist). I hope Apple fixes this as the 1GB adapter is sold at Apple Stores and doesn't work with this config.

@J1SG70 so to confirm you purchased the 2.5 gb ethernet adapter to get 979 Mbps download speed. Is that correct?

Here are some discussions of Ethernet adapter testing, FWIW:

https://forums.macrumors.com/threads/studio-display-usb-c-ethernet-adapter-performance-issues.2338556/

The only variable left is the dongle. ON my iMac with the same cables, connections, etc. no issue. Any Mac though that needs a dongle, there's issues.

I'm not comparing wifi with wired. All comparisons are wired. I'm not using a USB cable, I'm using a Belkin adapter as described above, the one from apple.

Seems like the Belkin GbE adapter might have an issue that the 2.5 GbE adapter doesn’t.