2020 iMac 5k - 10G ethernet not working

If you’re getting self-assigned, your DHCP is not playing well, or your host is badly botching the request, or you’re not getting to the DHCP server.

Given your report, there should be differences between the working and non-working states, for whichever en* device you’re using:

ipconfig getpacket en0

Check switch firmware and update, and check the DHCP server logs, too.

That static with a designated router also fails is not an auspicious sign; that’s either the host IP stack gone bad, or problems with the cabling, the switch, or the router.

Not having visibility into the switch port makes this more difficult too, unfortunately. Does your unmanaged switch have link speed indicators on the port? That might provide some clue when working or not-working.

Yeah, install macOS on an external, boot that, and see if that works.

Your planned other 10 GbE client test is also a good one.

Does physically un-plugging and re-plugging the patch cable clear the self-assigned wedge?

Absent some debugging luck, or maybe some missed setup step, I don’t know that this is going to get sorted here. What you have should work, but without a view into the switchport?

No 16-port 2.5 GbE / 10 GbE switch is listed at the NICGIGA vendor’s website, so details on that are unclear. The NICGIGA unmanaged switches don’t seem to have firmware, either.

For those following along at home and (like me) unfamiliar with NICGIGA…

Here’s a review of what seems closest (albeit 8 ports and POE): https://www.servethehome.com/nicgiga-s25-0802p-8-port-2-5gbe-and-2-port-10g-poe-switch-review/

Here is an aggregate listing and review of the lowest-cost 2.5 GbE switches: https://www.servethehome.com/the-ultimate-cheap-2-5gbe-switch-mega-round-up-qnap-netgear-hasivo-mokerlink-trendnet-zyxel-tp-link/

Looks like NICGIGA, VIMIN, and ienRon (and probably some AliExpress offers) all share common sources for at least some of their products, too.

As for the mesh part of this (and that’s very likely involved here as that looks to be the local DHCP server), the TP-Link DECO BE95 mesh router does have firmware, and there is an update from June 2024. Is that firmware loaded?

I don’t have an analog to this configuration though, as the 2.5 GbE switching gear I have access to is mid-range and managed and all from the same vendor as the mesh, firewall, DHCP server, and related.

Quite a chop suey mix. How about a picture?

The mesh router is the most-likely culprit IMO. It’ll probably work without - swap it with something less exotic (at least for troubleshooting). Or see if it’ll work minus all the switch-wall-cat-cable-jazz i.e. direct-connect (probably will).

Good luck!

hcsitas wrote:

Quite a chop suey mix. How about a picture?

The mesh router is the most-likely culprit IMO. It’ll probably work without - swap it with something less exotic (at least for troubleshooting). Or see if it’ll work minus all the switch-wall-cat-cable-jazz i.e. direct-connect (probably will).

Yeah; a description of the network would be goodness; what’s where, for the major pieces. I’d hope the switch is directly off the core router (and the core router is presumably also DHCP server), and not dangling off the mesh somewhere else, for instance.

This is incorrect. Ethernet is downwardly compatible. As such, the same computer that supports 10Gb/s also works with 100Mb/s or 1000Mb. I have plugged another computer's 1000Mb/s port directly into a 2.5Gb port on my router without issues. I currently have an 8-port 10/100/1000 unmanaged switch plugged into that same 2.5Gb port with everything from printers, to computers.

We are having exactly the same issues with the same type of iMac (my wife's) on our network. I'm troubleshooting internet issues (momentary internet drops, non-loading pages) with a mixed PC/Mac environment. The PCs will connect via ethernet, the Mac will not (two ports - one on the iMac, one on a HyperDrive Hub). Neither wired connection works, though it will show up as a wired device on the Netgear admin interface.

nemo837 wrote:

This is incorrect. Ethernet is downwardly compatible. As such, the same computer that supports 10Gb/s also works with 100Mb/s or 1000Mb. I have plugged another computer's 1000Mb/s port directly into a 2.5Gb port on my router without issues. I currently have an 8-port 10/100/1000 unmanaged switch plugged into that same 2.5Gb port with everything from printers, to computers.

Ethernet standards allow for backwards compatibility, but I do not believe that they demand that each and every implementation provide backwards compatibility with every possible lower speed.

The Technical Specifications for your iMac say this:

iMac (Retina 5K, 27-inch, 2020) - Technical Specifications - Apple Support

"10/100/1000BASE-T Gigabit Ethernet (RJ-45 connector). Configurable to 10Gb Ethernet with support for 1Gb, 2.5Gb, 5Gb, and 10Gb Ethernet"

On the M1 Pro and M1 Max Mac Studios, 10 Gigabit Ethernet is standard.

Mac Studio (2022) - Technical Specifications - Apple Support

"10Gb Ethernet (Nbase-T Ethernet with support for 1Gb, 2.5Gb, 5Gb, and 10Gb Ethernet using RJ-45 connector)

Very similar wording. It is well-known that the 10 Gigabit Ethernet ports on those Mac Studios do not support running at 10 Mbps and 100 Mbps speeds. Of course, the iMac could be using completely different 10 Gigabit Ethernet circuitry than the Mac Studio, but if the 10 Gigabit Ethernet implementation on the iMac does support connecting at 10 Mbps and 100 Mbps speeds, Apple missed a chance to advertise that in the specifications.

The Ethernet dongle isn’t the real thing, IMO n/a. Additionally, it looks like you’re pumping too much traffic through the solo 5G Verizon wireless which is susceptible to things beyond your control, and the highly-spec’ed and marketed but otherwise untested and unverified TP-Link box which also appears overloaded with traffic.

The only way to isolate your Mac from all these variables is to test on an internal network with real 10G ports all the way, using direct-connect short cables on both sides (and without anything else except a non-exotic router connected).

In other words, remove the Verizon + TP-Link Chop Suey from your picture and test with only the switch, suitable non-exotic router, Mac and another 10G device that can receive and send files. Until that happens, the Mac IMO is not suspect, an amused spectator at best.

Reinstalling MacOS is an essentially hail-Mary pass, nevertheless worth a shot given you’re already out of timeouts. That said, I seriously doubt it’ll make any difference.

Good luck! I’m outta here 👋

iMac (Retina 5K, 27-inch, 2020) - Technical Specifications - Apple Support

Specifications say that if you have one with the 10 Gb/s Ethernet option, that port supports "1Gb, 2.5Gb, 5Gb, and 10Gb Ethernet" speeds.

It does not support 10 Mb/s speed or 100 Mb/s ("Fast Ethernet") speed, so if you plugged your iMac into a router port that could not support at least Gigabit Ethernet speeds, you would not get any connectivity.

You show your router as having mostly 2.5Gb ports, including the one connecting it to the iMac.