Ethernet port not working with a Gigabit switch

I have had the same issue over the years after the warranty was up so a logic board replacement was not an easy option. After doing a series of tests using different cables (Cat5e-Cat7) I found that in my case only Cat7 worked reliably with Cisco and NETGEAR Giga switches. I was able to use Cat6 without issues when connected to an AirPort Extreme so in my case it appears to have been related to cable discovery and could likely be fixed with firmware (which has never been done and will likely not be done at this point).

My only recommendation for those still frustrated would be to pick up some Cat7 cable and give it a try. It will cost a few bucks but there is little risk as you can still use the cable anyway.

I gave up on this awhile ago and just been running wifi but am worried if that goes what to do. I now can't connect at all with ethernet even set to 10. I been messing with Yosemite beta, and it has a wifi bug on my install so it won't connect. Thats what made me think about ethernet. If anything the problem gets worse. Running a D link router now from Verizon. My airport extreme got took out by a lightning storm ( I think not totally sure).

Sorry for the double post couldn't find the edit button. I ran some test found out my ethernet port on the back of my early 09 mini just gave up the ghost. It don't work thats why it doesn't work. 😁

I got four LAN ports on the back of my d link modem run one end of ethernet cable into number one port and the other to three or whatever. The front panel port lights come on so the ports are good and the cable is good. Next test was to really make sure I brought in my apple tv and just plugged it in, and the ethernet the front LAN lit up. Does not on my mini whatsoever. Dead as a hammer.

Folks,

Nice to see us geeks still trying to solve this problem seven YEARS on.

My mid 2007 iMac is a wonderful machine and I would purchase it again in a second. But it seldom does Gig-E. My latest attempt is to use a new *short* CAT-6 cable connecting the iMac as the only wired client to a brand new tower style Time Capsule. No dice. 100Mbps only; forcing to 1000Mbps is equivalent to cutting the ethernet cable. Previous attempts included older Time Capsules, newish (e4200) Linksys Cisco router, and using a TP-LINK TL-SD 1016D Gig-E switch between them. No dice.

I think I got Gig-E working once with a crossover cable to a 17-inch MacBookPro. O joy!

I'm gonna try the CAT7 cable idea of a previous poster.

Hope springs eternal. . .

Ben

I recently had to rewire part of the building I work in to resolve a cabling issue. I knew there was an issue and knew it was preventing 1Gbps. However I can provide the following general guidelines based on years of experience with cabling networks.

1. 100Mbps Ethernet only needs four wires, due to this it was possible to get 'splitters' to run two 100Mbps devices via a single 4-pair cable run, a splitter had to be used at each end, 1Gbps Ethernet however needs all 8 wires. It is rare these days to see such splitters but as part of solving the network problems at the office I work at I did find a couple still in use and had to get rid of them, see http://www.radioshack.com/product/index.jsp?productId=16577336 you will note it is sold as a pack of two because as I mentioned you need one at each end
2. 1Gbps Ethernet needs Cat5 or better cabling, I normally use Cat5e as there is little or no real world benefit from using the more expensive Cat6 cable. However to go a full 100 metres with 1Gbps Ethernet requires Cat5e, in other words Cat5 can do 1Gbps but not over as long a run, as most people will not know the actual lengths after they have been installed clearly one should always go for Cat5e to be safe
3. The order of wires used is important, firstly to ensure end to end connectivity works, and secondly to prevent crossover interference, I always use the AT&T 258A wiring scheme (aka. T568B) and never have problems, see http://www.cabling-design.com/references/pinouts/t568ab.shtml#B just using the same colour at each end to make it a straight through cable might ensure connectivity but does not prevent possible crossover interference, the number of times I have seen people do this and then have problems...
4. An issue which is much less likely to cause a problem is 'un-twisting' too much cable at the end(s) when fitting to a socket or fitting an RJ45 plug, the twisting of the wires is there for a reason which is to prevent crosstalk interference, this is why using the right colour to the right pin is important because it ensures you are using both halves of a pair of wires together in the right places, note: the diagram linked to above for an RJ45 plug shows too much cable has been untwisted, in this case we will ascribe it to 'artistic license'
5. All parts in the link have to be Cat5 (see point 2 above about why you should really use Cat5e) or better for 1Gbps, this means the patch panel in the rack, the wall socket, the cable between the patch panel and the wall socket, the patch lead between the switch and the patch panel, and the patch lead from the wall socket to the computer. If even part of this is wrong then you may have problems
6. The official maximum length in total including all patch leads for a connection from a switch to a computer is 100 metres. If you have a length of 100 metres from the wall socket to the patch panel in the rack, and then have a 1 metre patch lead from the patch panel to the switch, and a 2 metre patch lead from the wall socket to the computer your actual total length will be 103 metres and will exceed the official limit. I have seen even brand new buildings and installations get the total lengths wrong (this was tested, proved and resolved by using a special cable tester to measure the total length)

In my recent case the cabling was very old Cat3 and known to not be 1Gbps compatible, the switch was a 10/100/1000Mbps auto-sensing switch as were the computers and printers. They would therefore intermittently detect the switch could do 1Gbps and try to use this speed, however the Cat3 cable was not able to cope and the link would fail. I had to manually set devices to 100Mbps only - until I got the wiring replaced completely along with the patch panels and wall sockets - all being Cat5e.

I was using Cat-6 patch cables between switch and patch panel and Cat-6 cable between network wall jack and mac-mini.

Could not use the network port, it just said no cable attached. Changed to Cat-5e cables on both ends and now everything works fine.

Are using the Cat-6 cables for all other equipment without issues.

Yet another user here with same issue. 2012 Macbook Pro. Have tried multiple Cat5e cables (don't have any Cat6, but that is not limiting factor for a short cable).

Connecting to Netgear M4100 switch. The port is good, as I have tested GB with my Asus router. Even plugged Macbook Pro into Asus router and it shows 100mb, not 1000.

So two GB devices, multiple cables, etc. and no solution. Help Apple....

I have an 2.7 GHz i5 iMac which also will not connect to the 1G port on a DrayTek 2820 router. Check:

Disconnect ethernet cable from rear panel of iMac, connect to MacBook Pro. ifconfig shows: "auto select 1000baseT full duplex, flow control" both lamps show on 1G router port confirming 1000BaseT connection. This works for OSX 10.6.8, 10.9.5 and 10.10.2 on MacBook Pro.

On the iMac, manually select 1000baseT, full duplex, flow control and message returns: Ethernet not plugged in. Change to 100baseT and connection opened - router lamps confirm connecton at 100baseT. Conclusion: (a) not a cable problem, (b) not an OSX problem, (c) not a problem with this iMac since reports on this thread show this problem is common to iMacs (d) it is an Apple problem and maybe a firmware patch to the NIC card (BroadCom 57795-B0) may be needed, or a patch to AppleBCM5701Ethernet.kext may be needed.

I notice that the MacBook Pro uses nvenet.kext which is also available on the iMac in the IONetworkingFamily Plugins directory

An addition to my note dated Mar 3, 2015 11:22. Today I borrowed a length of ultra-high quality cable: Nordx/CDT IBDN GigaFlex PS6LX Modular Cord Solid Core. Result: instant connection at 1000BaseT. It seems that the BroadCom NIC is extremely fussy and only the very best CAT 6 cable will do.

Note the comment in http://etherealmind.com/ethernet-autonegotiation-works-why-how-standard-should-b e-set/ that auto negotiation should always be used for gigabit ethernet. Manual selection should not be used.

Problem solved. (Relief)

Just installed fiber Giga internet to the home.

mid 2010 21.5" iMac (Yosemite) would not connect via a 25' Cat6 cable to a Netgear R6300v2. It would only handshake at 100baseT. Worked great at 100mbs however, so I knew it wasn't the card/firmware/OS, but what about the cable?

Changed to a higher quality 10m Vandesail CAT7 cable off Amazon. BINGO! The Cat7 cable has much better shielding between each pair and better connectors compared to a Cat6/5e/5.

My guess is that the Broadcom 5764-B0 NIC in the iMac is very picky about it's 1000baseT connection.

My guess is that the Broadcom 5764-B0 NIC in the iMac is very picky about it's 1000baseT connection.

My experience is similar to so many others here. The Mid-2011 iMac in my office is running Yosemite and has the Broadcom 57765-B0 NIC installed. After recently upgrading to fiber internet, I found the connection was 100MB duplex. A Windows 7 Pro VM installed under Parallels, however, makes a 1GB connection. The only difference here is the OS. All of the hardware is the same. If the NIC and / or it's firmware were rejecting the GB connection under one OS, it would as well under the other. Perhaps it is OS X that is picky about the connection.

An update to my previous post (unable to find edit function to add an update):

I switched out the ethernet cable from the NIC to the router, and it connected at 1GB duplex. The newly installed cable is nothing special, just another used ethernet cable that was laying around. Since Windows 7 was already connecting at 1GB with the old cable, but OS X would not, it seems to indicate that it is the OS that is the source of the connection issues, not the firmware or the hardware itself. Even if it is just that OS X is being more finicky about the quality of the connection than Windows 7, which could be viewed as a positive.

hello, I came here after searching on google, I have the same problem and can't find out a way.....

Imac 6,1 and gigabit switch. snow leopard installed and only going at 10 mbps......at 100 mbps it is going very unstable, connecting-reconnecting more times in few seconds.....gigabit never seen at all......

I also installed windows 7 on bootcamp, but the situation is exactly the same, at same speeds.....also tryed a linux live cd......the same

I tryed to change switch, and many cables, nothing changes....

In my opinion it is a matter of firmware, not operating system, because different os should use different drivers...

Of course, the system is upgraded to latest apple official firmware.....

It is really a shame.....

I can see this is an old thread but I just encountered this problem and found an answer - at least for my case. I used bootcamp to install Windows and then installed the Broadcom Card Management Software (which is sadly only available on Windows) and ran the diagnostics - what I found was that one of the four wire pairs of my Cat6 cable was showing as 'Short' i.e. short circuited. Then I ran the diagnostic again with the cable disconnected - same 'Short' status again for that pair (4th pair). The other three showed the correct info each time - 'Good' when connected and not connected when the cable was pulled out. So it seems my Gigabit ports issue is down to poor manufacturing quality like they didn't bother to test Gigabit functionality before shipping ... not really very impressive. My Mac was even bought in the US. Seems my only option is to buy a USB to Gigabit adapter - which won't get that great performance but hopefully better than 100Mb.

Bought a UGreen USB3 Gigabit adapter and it works - but the performance is quite inconsistent - actually worse for copying files around my home network than the built-in adapter working at 100Mb .... quite frustrating.