Leopard - Gigabit lan not working at 1000mb/s


macrumors newbie
Original poster
Oct 30, 2007
I succesfully installed Leopard on my iMac Intel 20" (new install).
Everythings seems working right except for the built-in Ethernet connection SPEED.
On the same machine with Tiger configured at 1000Mb/s FullDuplex transfer rate on my LAN was very well... reaching about 50 MBytes/sec.
Now with Leo i tried different settings (with and without flow control, mtu speed 1500 or 9000), but the behaviour is the same:
at 1000T it works but VERY slowly and the net monitor show
up and down transfer rate (few mb/s)
i got the max speed ONLY setting "100Mb/s FullDuplex" ( 10 MBytes/s) : (

anyone can help ?



macrumors newbie
Jan 11, 2008
Same problem here

Here too. As soon as I upgraded to Leopard on my Macbook Pro I am now only running at 100Mb/s. I can also tell this by looking at my network switch which shows yellow for 100Mb/s and green for 1000Mb/s.

Anyone out there have a solution?

Note: MACBOOK PRO, 3 GB RAM, 10.5.1


macrumors regular
Jul 16, 2002
Calgary, AB
Ensure you are using Cat 5e or Cat 6 cable for each segment. I leave my computers (with Leopard) on AUTOMATIC, and they will run at 1000 Mbps. If your computers are defaulting to 100 Mbps with automatic, you may need to upgrade your cables or connection.

Apparently some Cat 5 (not 5e) cables can work at 1000 Mbps, but my iMac would only run at 100 Mbps on automatic until I switched the 7' cable I was using (from the iMac to wall jack) to Cat 5e.


macrumors 603
Aug 15, 2001
The Cool Part of CA, USA
Perhaps Leopard is more picky about network connections? The CAT5 vs 5e thing might be possible, but unless you're using really old cable I haven't even seen non-e CAT5 for sale in years.

I'm also running 1000BT without issue under Leopard (hand-made CAT5e cable), so it's not a universal issue, at least.


macrumors member
Sep 18, 2008
Milton Keynes
I have the same issue, but it appears to be cable related some how.
I bought a 350m Box of CAT6 to cable up my house. and ran 2 wires into my bedroom 1 for Xbox 360 and the other for my mac mini ( i know cat6 wont benefit my 360 :) ).
All cables were cut to the same length and crimped correctly, I plug one of the cables in and when checking network configuration says automatic 100MBs but then when trying the other cable says automatic 1000MBs.
Not such an issue for my bedroom but the 1 cable going to another mac mini in my front room is only saying it's 100Mb :(
guess i will just have to cut some more cable and try again :confused:.
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