Mac Mini wired internet connection drops in speed, reboot restores?

[MrDoh]

I'm using a Mac Mini with an M2 Pro chip set as my desktop computer. I have the latest Tahoe release on it, macOS 26.5. I was using only the ethernet cable connection for some time to see if the problem I'm having recurred. It did.

The problem is that occasion the mac's internet speed will drop from about the normal 365Mbps from my ISP to about 85Mbps. About a 75% drop in speed. When I notice this, I restart the system and it comes back up at normal speed. Other devices here don't do this, they just run along happily at the normal speed. Don't think the problem is a cable or other hardware problem, or a restart wouldn''t fix it every time.

I don't know where to start to troubleshoot this one. Seems like it's most likely a software problem of some sort. Any ideas what might be going on, or how I might get to the bottom of this. It isn't a showstopper, just annoying to have to deal with.

 

[MrDoh]

Trying a couple of things...have changed the Ethernet Network TCP Details "Hardware" "Configure" setting from automatic to manual. As well as the IPv6, switched that to manual as well. Hoping that this will help, I guess time will tell. Seems to have helped some other folks.

 

[monokakata]

I experienced something similar, and fixed it by going to the Ethernet tab on Network, Details, and then not just changing to "Manual," but making sure that the "energy efficient" options were not selected. It seems that this can take a Mac offline and then back on again. Perhaps this is happening very quickly or in such a way that your effective speed drops.

 

[MrDoh]

Not seeing energy saving/efficient options under "Network", "Ethernet", "Details"...likely because my Mac isn't a laptop? Not worried about battery life for a desktop, I guess 🙂.

No recurrence of speed drop since the changes I made yesterday. Time will tell.

Oh yeah, I just installed "orb" to try and catch this when it happens, with active speed monitoring. Might be helpful in narrowing down possible causes.

 

[monokakata]

I'm surprised. My Mac is a Studio, not a laptop. I'd think your Mini would behave the same way. Oops! I didn't say you should go to "Hardware" after "Details." Sorry. See attached, where I show it set to the wonky option.

 

[MrDoh]

Interesting...the 2 choices that I have for "Duplex" are "Full duplex" or "Full duplex with flow control", that's it. No "energy-efficient-ethernet" in my settings. Probably would have turned that off if I had it as a choice after my experiences with disks and network interface power-saving settings.

Can't account for the difference, on the latest Tahoe release here, 26.5. Says "Your Mac is up to date" under General -> Software Update. Do you perhaps have "Beta Updates" turned on, and are running a Beta version?

 

[monokakata]

That is hard to understand. My Studio is on 26.5, but as I remember, the "energy-efficient" choice has been there since early Tahoe.

Perhaps it has something to do with what's at the other end -- in my case, a Netgear 2.5g switch.

I think once I had my Air (also 26.5) plugged into ethernet via an adaptor and I didn't see that option.

Sorting it out probably won't help with your issue, but I'll try to find time today to see what's happening.

 

[Bill_D]

I had a similar problem with a 2018 Mac mini. Turned out the Cat 5e ethernet cable was marginal. The system would connect at 1000Base-T on reboot, then sometime later drop to 100Base-T for no apparent reason. A new ethernet cable fixed it.