2015 iMac only at 100mbps

robertfrombuderim wrote:

The bottle neck is nowhere else.

Its the onboard adapter which is not running at Gigabit for the ethernet. The cable is CAT 6, my Netgear router supports gigabit speeds as is evidenced by all other devices running at full speed - 1000.

I have used several different ports in the office to check the port is OK . Every time the 27" late 2015 imac gives 100 speed. As soon as I manually change it to 1000 speed it drops and tells me the cable is disconnected.

This has nought to do with the ISP either. Its a hardware issue with the onboard adapter.

So is there a driver update for the on board ethernet ?

There is no driver update, other than running MacOS updates which I assume you have, your iMac should be on Monterey and fully updated. I have a 2015 iMac and have connected it via ethernet as well as WiFi and we have a 300 Mbps plan and all devices, including this iMac, consistently show 350 Mbps via WiFi (with a mesh Linksys router). So I guess our provider is giving us a little bonus there. But you should have 802.11ac which is fast. You can check your WiFi on the iMac by option-click on the WiFi symbol on the menu bar at the top of your screen, mine shows TX Rate 1300 Mbps and 802.11ac (also in About This Mac => System Report look under WiFi you should see same TX Rate). For me that is the speed of my WiFi but my internet connection is capped at 350 Mbps by my plan. Also you should see very high signal/noise ratios, e.g. RSSI -36 dBm and noise -92 dBm, which is about 56 dB signal/noise, and make sure the channel number is showing 5 GHz and some reasonable bandwidth like at least 40 MHz and preferably 80 MHz. If your signal/noise ratio is not good, or you are stick on 2.4 GHz instead of 5 GHz, or the bandwidth is being reduced (sometimes routers will do that for signals that have lots of interference from other WiFi networks), that might explain the lower data rate.

That's for WiFi. If you get similarly low speeds with ethernet then I would check the cable, make sure it is Cat 6 or better. If ethernet is still bad when another computer gets good speeds with the same cable and connection, then I would suspect something in your Mac is broken.

One additional test: boot into safe mode and recheck.

Do you have a router between your cable modem and computer? If so double check that. I was previously using a AC 1200 router, but despite advertising up to 1200Mbps Wifi the cheap stuff only had 100Mbps Ethernet which was a bottleneck.

Your iMac supports Gigabit Ethernet. If you are only realizing 100 Mb/s the bottleneck is elsewhere. Look for anything between what your ISP provided and your Mac.

You can choose to manually constrain hardware performance to something less than the maximum supposed speed. Read Use Gigabit Ethernet on Mac - Apple Support for example, but the default is Gigabit.

Thanks all for your responses. However the issue I am dealing with isnt one of internet speed per se.

I have a Netgear 24 port switch which I run all ethernet ports through for the home network.

Every device has an ethernet adapter capable of 1000 whatevers per second - a gigabyte per second.

The switch shows every other device running through the switch - between the ethernet port and the switch - at 1000Mbps. The only one that doesnt is the iMac which chugs along at 100Mbps even though it is capable of 1000Mbps - no matter which cable or ethernet port I use.

So I can now only assume its a fault on the onboard ethernet connector.

My Late 2015 21.5" iMac consistently get's 400-450 MBps wirelessly on a 600 MBps plan.

But that speed was obtained only after I upgraded my router to one with gigabit Ethernet Ports, 1,500 square-foot Range, 10 Devices, MU-MIMO model.

The modem was upgraded to DOCSIS 3.1 Cable Modem to mate with the router capabilities.

Unless you have the gear required to allow the speeds you're buying, you'll not get them. And, the best you can expect for a given plan is about 70% of what you're buying. In your case a max on maybe 70 MBps. And that will change from pretty much minute to minute based on many factors influencing your signal. Internet signal "overheads" take their toll.

The tech may be right, but that's just the speed they're pumping into the line at origin. Even then, you'll never see more than about 70% on a good day ... about 650MBps or so. And to actually use that speed, you have to have a modem and router capable of doing so.

On a Wired 3' Ethernet connection, my 2016 MBP gets over 900MBps consistently on a 600 MBps plan. Xfinity/Comcast had no explanation for that.

The bottle neck is nowhere else.

Its the onboard adapter which is not running at Gigabit for the ethernet. The cable is CAT 6, my Netgear router supports gigabit speeds as is evidenced by all other devices running at full speed - 1000.

I have used several different ports in the office to check the port is OK . Every time the 27" late 2015 imac gives 100 speed. As soon as I manually change it to 1000 speed it drops and tells me the cable is disconnected.

This has nought to do with the ISP either. Its a hardware issue with the onboard adapter.

So is there a driver update for the on board ethernet ?

Note that network interface speeds are specified in terms of bits per second.

Even if you could fully saturate a Gigabit Ethernet link, and there was no overhead (there is always some overhead), you could never exceed 125 megabytes per second. If you are estimating your network speed by timing a large file transfer, be sure to take that into account.

The Ethernet port on any of the 2015 iMacs would support 10, 100, and 1000 megabit per second speeds.

robertfrombuderim wrote:

and are you getting 10000Mbps? or 100?

I'm not using Ethernet. The jack that the DVR and cable modem use is in a different room from my office, so I've been using Wi-Fi for many years.

and are you getting 10000Mbps? or 100?