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My Mac mini is connected to my router/modem by Ethernet. I want to know how fast the connection speed is between the Mac and the router.

Obviously, I can use a website like Speedtest.net to get my Internet connection speed, but that doesn't tell me whether the Ethernet connection is a limiting factor, or how much 'spare' capacity there is for local traffic.

The mini serves to other devices. The Ethernet is over a powerline, and the cables are ancient, so may not be optimal.

If I were using Wi-Fi, then the data throughput is shown by holding Alt and clicking on the Wi-Fi menulet icon.

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  • What is your EOP equipment rated for? The actual throughput is almost always far less then advertised. How accurate are you trying to be? Sans appropriate physical wire testing equipment, the only thing I can think of is to copy a large file created with dd and /dev/random of a appropriate size to easily preform calculation after timing its transfer from the mini to another device. This of course is not the same as testing just the wiring but if will give you something local verses Speedtest.net data to chew on. Sep 6 '19 at 14:43
  • The equipment is rated 500Mbps (BT Broadband Extender 500). Speedtest gives me 47Mbps. Network Utility gives the Link Speed as 100Mbps. It's configured to be Automatic, and if I change it to 1000T, the Ethernet disconnects. I'm just looking for a rough idea.
    – benwiggy
    Sep 6 '19 at 17:26
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As a rough idea - your speed must be somewhere between 47 and 100 Mbps. Must probably it is 100 Mbps.

If you want to test, get a second computer and take the connection out of the router and plug it into that. Then you can start a transfer from one to the other and measure the speed.

One of the most common tools for making such a transfer and measuring its speed is called "iperf". You can install it via HomeBrew (if you have that), or you can download the Mac binary from their webpage.

After installation, start Terminal.app on both computers and run:

iperf -s

on one, and:

iperf -c 1.2.3.4

on the other. Replace 1.2.3.4 with the IP address of the first computer.

After a short while it will tell you the bandwidth in Mbits/sec.

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Found an app called LAN SpeedTest, which unsurprisingly is well-suited to the task.

Running it on another computer, connected directly to the router by Ethernet, and writing/reading a chunk of data to a shared folder on the Mini, it gives Read speeds of c.60Mbps and Write speeds of c.50Mpbs.

Why it's so low is, of course, another question.

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  • Don’t connect it via the router - connect it directly to the cable that otherwise plugs in the router from the Mac Mini. Don’t use a testing program that stores data on a shared folder - then you’re no longer testing network speeds, but multiple things at once. Use the testing method in my answer, and you get the real network speeds measured.
    – jksoegaard
    Sep 7 '19 at 10:58
  • Surely the router itself is an important part of the equation in determining network speed? If I remove the router altogether, then I'm just testing the cabling between two Macs, which might be much faster. I'm presuming that the disk speed of the Mini (2018) is not going to be a limiting factor at this speed.
    – benwiggy
    Sep 7 '19 at 20:13
  • Well, in your original question you asked how fast the connection between the Mac and router is - this is what I answered. If you want to know how fast it is when going through the router and out a different connection, you can measure that too - but that’s a different thing.
    – jksoegaard
    Sep 8 '19 at 11:09
  • And no disk speed is usually not a limiting factor here, but protocol overheads and inefficiencies usually are. Therefore it is not a good idea to measure networking speeds by saving stuff on a shared folder. Avoid disk access at all and get a true measurement of networking speeds.
    – jksoegaard
    Sep 8 '19 at 11:10
  • I gave the program a try - but its name is misleading. It does NOT measure the LAN speed, it measures the transfer speed of files to a file server. So you (a) need another computer that acts as a file server, and if that one is slow, you may get slower results than what your LAN connection supports. I expected this tool to simply make a TCP or even UDP speed test to a peer computer (which may as well be the router itself, using the various echo protocols), as that's what the name suggests. Jul 16 '20 at 10:19

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