Speed Drops Through Switch on One Line

[Spike666]

I rent a house that was finished less than three years ago and has ethernet installed. I am running two Deco units on the ethernet plus the master Deco at the router, one Mac on the ethernet and one Deco with wifi. There is a switch, TP-SG1005D, after the main Deco that the two Decos connect through. The ethernet for the Mac goes direct from the gateway to the panel.

I get 550mbps at the Mac, and similar at the wired Decos, they do close to 500mbps for the wifi connections so they are obviously seeing full bandwidth from the Decos. However, if I put a switch on the line to the Mac, the speed drops to 100. I have tried it with the router at the gateway, at the wall outlet near the Mac, and at the Mac, and it always drops. I have tested a Deco in place of the Mac and it also sees a speed drop.

I have two identical switches, I have tried both of them, swapping them out. I have numerous ethernet cables and have tried many of them. I bought an ethernet cable tester recently and everything checks out, including every cable that is involved to the Mac and to/from the switch.

The only other wired device I have is a television, which shows similar speeds with and without switch, although it is limited to 100mbps.

I'm a bit stuck on this, it doesn't make sense to me unless there is a cabling problem the tester doesn't see.

 

[tgl]

"It's limited to 100Mbps" always makes me think first of faulty cables, but it seems like you eliminated that theory.

I see that the TP-SG1005D advertises "green ethernet", which I assume means EEE (IEEE 802.3az). I have heard reports of that feature causing compatibility problems. You might need to try a switch without it.

 

[Spike666]

Thanks. I can try to pick up another switch, may take a while as I don't live close to a store that has them. However, it's still odd that every other connection through the switch works fine.

 

[degrub]

What link rate (not speed test result) does the Mac indicate when you connect directly and through the switch ? Either the link rate lights on the Mac and the ones on the switch may indicate as well as what is reported by MacOS.
What model Mac ?

There have been some issues reported with Macs on higher rated link rate switches that were only solved by manually setting the link rate in the Mac ethernet driver config.

Just curious, if the Mac reports 100Mb when connected to the switch, what do the other ports on the switch provide to other gigbit devices while the interposing switch is connected to the mac ? Do all the ports switch to 100 Mb ?

 

[Spike666]

Thanks for the response, you may have missed that I have tried using a Deco in the same situation and it sees the speed drop as well.

I did check the Mac, it's an M1 Mini running 15.5. When I go into the settings for the ethernet hardware, it is configured automatically, but if I change it to manual an d 1000BaseT, it's the same. But as I mention just above, I see a speed drop running it into a Deco. If I test the same Deco, it's doing about 480Mbps on wifi without the switch and a little under 100 with the switch, so the behavior is the same. And it's just this one line, so I am not sure what is going on.

I don't have any other gigabit devices to test with, there's a Macbook Air which has no ethernet port and doesn't seem to work with USBC to ethernet adapters. There are a lot of wifi devices but none with ethernet connections.

 

[degrub]

Something to help diagnosing - draw a sketch of all the components - cables (A,B,C,etc) switch and port used, deco (A,B, C, etc) , router, wall cables and wall terminations, central panel terminations and how it is all connected. Do your testing by moving things around , but in a very structured way. write down the result for each test. SEE what change the issue follows - cable, client, wall plate, central location termination, switch, etc.

Again, check what the link rate lights on the switch and devices indicate. It is a different issue if getting slow speed test result versus getting a different link sync rate.