I'm looking to see whether the community has any networking experts available to help resolve an issue I'm having with OS X. I recently signed up with AT&T's Gigapower service which is roughly a 1Gbps symmetric internet connection. Upon activating the service, I noticed I wasn't getting the guaranteed speed on my Late 2014 Retina iMac. Instead speed tests were showing download speeds ranging between 250 and 450 Mbps and upload speeds limited at 60Mbps. AT&T sent a couple of technicians to confirm that their service was working as advertised. They plugged an older Dell laptop running windows directly to the modem and sure enough were seeing the advertised transfer rates of around 800-850 Mbps for both upload and download. In so doing, they ruled out any issues with the ethernet cable my iMac was using by plugging the same ethernet cable into their Dell laptop. This prompted me to boot into Windows via my BootCamp partition to run a speed test using the same iMac, and sure enough my iMac running Windows 8.1 was getting 950Mbps transfers. I will also note that I have a 2015 Macbook Pro which I plugged in via ethernet and it has the same slow ethernet transfer speed while in OS X; thus, why my suspicions are revolving around the OS as the culprit. I called Apple's support line to see if they had a solution, and they weren't willing to troubleshoot the issue beyond having me reset the PRAM, boot into safe mode, and re-run the speed tests. Their suggestion was to blame AT&T's service, which I'm not apt to do at this point. In any case, any support from Apple on this issue doesn't seem to be an option. The Hardware tab in the Advanced settings of the Ethernet network configuration shows that everything is being configured Automatically with the following settings: Speed: 1000baseT Duplex: full-duplex, flow-control MTU: Standard (1500) I switched the configuration once to configure it manually while changing the MTU setting from Standard (1500) to Jumbo (9000) to see if that made any difference, and unfortunately it didn't. I would welcome anyone else's suggestions or any other similar experiences related to this issue if anyone has them.