MacBook won't pick up networking on ethernet

I've seen Ethernet interfaces begin having hardware failures by failing to establish link with some switches, especially at gigabit speed. When plugging my last MBP into the Cisco GigE switch at work (which it had worked with for years), it would keep cycling link up and down until I manually configured it for 100/Full. Leaving it set for full autonegotiation would work with other switches, especially 10/100 switches.

See if manually configuring your failing MBP's Ethernet speed/duplex settings for 100/Full fixes the problem connecting to the GigE switch.

If you can't get any connectivity over Ethernet and if a clean reinstall of Mac OS X doesn't fix it, then you have a hardware failure that needs repair.

As you have tested MBP2 in another network and it worked well, and as MBP1 works without issues, it might just be that your switch is a bit off and MBP2 too, so that together they simply do not get along but still work fine with other partners.

One possible test might is to try another switch, loaned from a friend or a shop, and see if this solves the problem. If it does, then the switch is the problem.

Another test is to use a USB network card on MBP2. If this solves the problem, you might be able to force Apple Store to replace your MBP2 card, or stay with the solution of the USB card.

From the information that you have provided I would suggest the problem lies with your router not with the MacBook.

Have you tried a complete factory reset of the router?.. If its a standard netgear configuration you will want to go to http://192.168.0.1

username: admin & password: password

locate the factory reset button somewhere within the administration panel. (alternatively Press and hold the Default Reset button until the power light blinks on (about 10 seconds))

You will then need to wait for the router to settle before re-entering your ISP login information to re-connect to the internet. (or running through the setup wizard)

edit: if other people have access to your configuration they may have blocked the mac address of your MBP that won't connect.. you will be able to find this in the netgear configuration too. you can also set a new admin password to prevent unauthorised access.

Manually configure MBP2 with an IP address in whatever subnet MBP2 and the server share (probably 192.168.x.x).

On MBP2, with no other network activity going on, open the Terminal and type "sudo tcpdump". This will show you all networking that can be seen (if any).

On MBP1, open Terminal and type "ping 192.168.x.x" where x.x is the address you set for MBP2. Does any activity at all show up on MBP2? If so, then ethernet has basic functionality and the problem is with routing. If nothing shows up on MBP2, then it is more likely a hardware or an MBP2 configuration issue.