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macrumors newbie
Original poster
Feb 20, 2014

I'm hoping someone can shed some light here or at least give me some new ideas before I pull out the rest of my hair.

We have a Mac Pro here - 5,1, 2 x 2.66 Six Core Xeons, 12GB RAM. Recently the network has been dog slow on it. Still working, just very, very slow. It's peaking at about 9MB/sec, whereas the other macs here are getting around 40-50MB/sec.

I have tried a LOT of fixes -
- Replaced the networking (cable and floor port)
- Added a third party network card
- Tried various "networking fixes" (turned on/off internet sharing, file sharing etc)
- Even reformatted and reinstalled the OS

All to no avail! We also recently acquired a machine of the same model that is working perfectly, so I thought I'd do a test and swap HDD's. The newly acquired machine still works perfectly, so I'm guessing I can put this down to hardware.

I guess my issue are -
Can anyone think of any reason it WOULDN'T be hardware?
Also, as I mentioned, the networking is still working, just very slow. If I put the mac in to be repaired, will they be able to diagnose and/or repair it?

Any hints or tips much appreciated! Thanks in advance!!

Gav Mack

macrumors 68020
Jun 15, 2008
Sagittarius A*
I've seen mischief with QoS enabled on the router but to do that it's bound to your Mac Pro's MAC address but you do have two ports, they would have to register both MAC's to handicap the speeds - is it the same speed in both ethernet jacks?

Jumbo frames issue, MTU..

Running an apple hardware test (aht) diagnostic on the network which is on your installation DVD.

I have used packet sniffers on the host computer in the past to troubleshoot slow network speeds but I've only done that on a windows box for the host machine or Cisco managed routers. If you have a mac only network maybe the mac only members on here can help..

Reno Richter

macrumors member
May 31, 2012
I assume you are on ethernet since you mentioned cable.
You mention other machines work fine.
I assume you plug the cable in a RJ jack in the wall and it comes out in a server room or network closet where there is a smart hub of some kind.

Tests I would run.
Change the cable in the hub to a different port in the hub or even a different hub if you have multiple hubs linked together.
Bring another computer that is showing good speed and plug it into the same port in the wall and see if it slows down.
The above should easily identify if the problem is your mac or the wiring hubs, etc.

We use the older mac servers that Apple stopped selling. In recent times two have lost network cards. Things would become painfully slow but do something you are not seeing and go totally deaf for a few minutes then recover. One a replacement card solved the problem. The other the issue was more serious beyond the card and we replaced the box with a Mac Mini.


macrumors newbie
Original poster
Feb 20, 2014
Thanks for the replies!!

Yes, they are all gigabit ethernet. I have ruled out everything back to the server room - new cable, different floor port, different switch.

The real clincher was swapping the hard drives between a known good Mac Pro and the dodgy one. Performance issues stayed with the hardware - i.e. the dodgy Mac Pro was still dodgy.

Hardware tests show no problems. The issue being the network "still works". It's just very slow.

I can see me taking it to an Apple repair centre and them saying there is nothing wrong with the machine.


macrumors member
Aug 11, 2008
Being a network guy, the first thing that comes to mind is that machine is perhaps not running at Gigabit speeds for some reason. It is possible that the Ethernet port is running at say 100Mb/s rather than 1Gb/s, either because someone specifically configured it this way in the Network system preference, or due to a hardware problem that is preventing it from negotiating 1Gb/s.

You should be able to see what it is currently running at by typing "ifconfig" in a terminal window.

Look for the en0: or en1: interface and you'll have something like this near the bottom: media: autoselect (1000baseT <full-duplex,flow-control>)

If if says something other than 1000baseT, like 100baseT or perhaps half-duplex rather than full-duplex then this is definitely a problem.


macrumors 6502
Jul 25, 2010
The network setting should have stayed with the hard drive. It has to be hardware. Try the hardware diagnostic that came on the install DVD if you have it. Otherwise, I'd run it by the Apple store if you have one nearby.


macrumors member
Aug 11, 2008
The network setting should have stayed with the hard drive. It has to be hardware. Try the hardware diagnostic that came on the install DVD if you have it. Otherwise, I'd run it by the Apple store if you have one nearby.

I agree, it should go with the hard drive so likely it is some sort of hardware issue. None the less taking a quick look at ifconfig could shed some light as to if the problem is link speed related and this could be useful information to show the Apple store folks.

9MB/s is suspiciously close to what you could get running at 100Mb/s link speed.

I wouldn't rule out that auto-negotiation settings are stored in PRAM. I've heard of a few cases where resetting PRAM was needed to convince a Mac to negotiate 1Gb/s link speed correctly.
Last edited:


macrumors 6502a
May 17, 2011
I had this problem with my Mac Pro 5.1 on the wired network right after I bought the brand-new machine. I could not figure out why. I also called the Apple Support but they could not provide any fix besides suggesting a trip to an Apple authorized repair center.

I then switched to WiFi on which the transfer rate was normal. Since then my Mac Pro has been on WiFi.
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