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First a little network diagram;

We have an ADSL router (Standard home broadband Netgear. DHCP, DNS and firewall disabled), connected to a gigabit switch (unmanaged, it just sits there and works). From that switch we have (among other things) a wireless access point, an OS X server running DHCP, DNS, firewall and other network services, and two MacBook Pro's (OS X Lion).

+------------+             +---------------+
|  Internet  |-------------|  ADSL Router  |
+------------+             +---------------+
   +---------------+    +------------------+        +---------------+
   |  Wireless AP  |----|  Gigabit Switch  |--------|  OS X Server  |
   +---------------+    +------------------+        +---------------+
                             |        |
                             |        |
                             |        |
                             |        |
          +--------+         |        |
          |  MBP1  |---------+        |
          +--------+                  |
          +--------+                  |
          |  MBP2  |------------------+

(MBP = MacBook Pro)

MBP1 is quite happy, it has an Ethernet connection and has its wireless turned off. I've never had any problems with it. MBP2, however, will not work at all on the Ethernet network. If I disconnect the Ethernet and connect to the wireless AP, it picks up DHCP and will browse exactly as it should, but even though it's directly connected to the same switch as the AP, it just sits there saying


I've tried going to Advanced->Renew DHCP Lease, I've tried setting the settings manually, but it just won't pick up the network.

Connecting to other Ethernet networks works fine, and both MBP's were bought at exactly the same time, have exactly the same spec and have had exactly the same things done to them. I've swapped Ethernet cables, ports on the switch, tried plugging it into the ADSL router, tried plugging it into the Ethernet ports on the wireless AP, it just won't work on Ethernet.

I'm at a complete loss, how would I even start to go about debugging this? Connected to Ethernet, even with a manual address, it can't ping anything (except


As suggested, I have re-installed OSX, and taken it to Apple Store, but since it's working fine on every other network we've tested Apple don't think it's a hardware fault. I've tried swapping the switch to an older 100Mb switch, same issue. However if I plug it into the back of the ADSL router it picks up an IP/DNS settings from DHCP and works fine (I've confirmed in the network settings that the DHCP was picked up from the OS X server not the ADSL router/anywhere else, even though it has DHCP and DNS disabled I wanted to make sure). I can connect to all the other clients on the network (Picking up network drives and Time Machine from the OS/X server, connecting to management on the AP etc.).

It's clearly something to do with the network but I'm not sure what, having tried different switches and Ethernet cables. I have full access to the network and server so I'm willing to do/try pretty much anything.

I'm not ruling out personal insanity, given the situation

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well written, researched, and illustrated. +1 :) – studiohack Jan 2 '12 at 17:15
Try increasing the log level for the DHCP service, and see what it shows when you connect the MBP. For a successful DHCP interaction, you should see a DISCOVER from the client, an OFFER from the server, a REQUEST from the server, and an ACK from the client. (Note that when renewing an existing lease the DISCOVER and OFFER steps are skipped, but that's not relevant here.) Knowing which steps happen may give a better idea where the problem is. – Gordon Davisson Jan 2 '12 at 20:04
@GordonDavisson Absolutely nothing in the DHCP log when I connect and disconnect the client. Though I assume this is caused by the same issue I'm encountering with a static address, complete inability to recognize a network connection past the end of the cable. – Smudge Jan 3 '12 at 8:56
When testing MBP2 in the Apple Store, have you used a Gigabit Switch? – harrymc Jan 5 '12 at 17:17
@harrymc Yes, tried with a gigabit switch and a 100mb switch, both working fine – Smudge Jan 5 '12 at 17:20
up vote 2 down vote accepted

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.

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I have tried replacing the switch with a different (100Mb/s) switch with the same issue. I'll grab a USB card and test that out. – Smudge Jan 6 '12 at 15:31
USB card worked, spoke to Apple and they're going to replace the network card. – Smudge Jan 7 '12 at 14:29
If that's the case, please accept his answer or mark the question closed. – Brett Dikeman Jan 11 '12 at 6:21
Another thing I was gonna suggest (just in case it didn't work) was to connect MBP2 to the same cable as MBP1 and see if it works there – Canadian Luke Jan 11 '12 at 21:59
@Luke: It says he did that. – harrymc Jan 12 '12 at 6:42

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.

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Tried manual hardware settings, no difference. I took it into Apple store but because they tested on their Ethernet network and it worked fine they say there is no fault. I'll try a re-install now and get back to you – Smudge Jan 2 '12 at 19:08
Reinstall did nothing, same error =( – Smudge Jan 3 '12 at 8:50
@sam Get thee to the Genius Bar! – Spiff Jan 3 '12 at 9:02

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

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.

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The router does nothing other than connect to the internet. I'm not resetting the entire network for one misbehaving client – Smudge Jan 2 '12 at 19:06
From your diagram it looks as though your router is providing IP Adresses to the rest of the network. is this correct? – Wezly Jan 2 '12 at 19:16
No, as described in the question we have an OS X server running DHCP, DHCP on the router is disabled – Smudge Jan 3 '12 at 8:50

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.

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