MacBook Pro M3: Ethernet limited to 100Mbps via adapters

<< All cables have 2 pairs of 4 in them. >>

Ethernet cables for use above 100 G bits/sec have Four twisted pairs in them. Any wire miswired from one of the two acceptable standards can cause speeds higher than 100 to be un-attainable.

Twisted pairs are made with the paired wires twisted around each other, in a way that the twisting patterns in each pair are different and not multiples of each other. Because the two wires are twisted around each other, no sources of noise can come between them.

This is One of the two allowed color-codes:

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have you tried the adapter sold at the Apple Store?

the one sold there now is a 2.5 G Ethernet adapter by Belkin.

stephankilgore wrote:

I just put an Ethernet drop in my office and have tried 3 different multiport adapters with Ethernet and cannot get beyond 100mbps. All cables and the adapters are rated and advertised for at least 1Gbps. All cables are cat6. No kinks or twists in them. All cables have 2 pairs of 4 in them.

If I plug directly into the AT&T router, I get 1Gbps speeds.

That sounds like a problem with the new ethernet drop.

Check the wiring in the new Ethernet drop. A wrong connection or a "not quite" connection on even one of the wires (at either end) could be the cause of the problem. It is easy to not fully punch down one or more of the wires; or if the connector isn't quite up to par it might not fully bite through the insulation on one of the lines. Or maybe there is a problem with the in-wall cable.

The new cable run is likely faulty, then.

A tool such as the following can be useful for verification and troubleshooting cable runs:

https://www.kleintools.com/catalog/cable-length-measurement/ethernet-cable-tester-kit-scout-pro-3-tester-remotes-and-adapter

(I use a different version of that tool for this task.)

Whether the fault is somewhere in the cable run, in the keystones on either end of the run, or maybe the patch cable from the nearest keystone into the AT&T box?

Semi-related: If you’ve not already worked with a passthrough crimper for these projects, they are wonderful:

https://www.kleintools.com/catalog/cable-tools/ratcheting-ethernet-cable-crimper-stripper-cutter-pass-thru

Speeds up to 100 use only two of the four pairs of wires, and baseband signaling, one bit per signaling interval.

When you need to jump to 1000, that uses a modulated signal with all four pairs carrying data and multiple patterns per signaling interval.

So a modest defect (such as a single broken wire) can mean that cable works for 100, fails for 1000.

MrHoffman wrote:

A tool such as the following can be useful for verification and troubleshooting cable runs:

That tool (an earlier version of it) has saved me a lot of time.