Why won't a MacBook Pro running Snow Leopard obtain an IP address (DHCP)?

Background: I am trying to connect my MacBook Pro to a business grade network where I do not have access to reboot the server, switches, or router.

Problem: The MacBook Pro (running Snow Leopard upgraded from Leopard) will not obtain an IP address via DHCP and repeatedly self-assigns a 169.xx IP address. I have tried restarting the computer, changing network ports and using different cables. Each time the computer has the same issue. I am able to connect to the same network via a wireless access point with no issue and other PCs (new to the network) are able to obtain an IP address without issue.

Question: Why won't my MacBook Pro obtain an IP address via the ethernet connection? Any suggestions?

BlueDevil

Posted 2009-09-17T16:22:55.933

Reputation: 386

So, by today did you get a solution for this? I'm having a similar issue where my mac sometimes won't get DHCP correctly, in two different networks. Anything else works fine, and static IP also makes the mac work. – cregox – 2010-04-23T20:40:12.950

To be sure the ethernet port on the MBP isn't hosed - are you able to get an IP on other networks (eg. your home network) – Chealion – 2009-09-17T17:01:15.530

I just set up a test network with a TFTPd DHCP server setup. Then connected the MacBook to my Lenovo x200 via a 10/100/1000 switch and activated the DHCP server (TFTPd). I then manually requested an IP address from the MacBook and saw the request show up on the Lenovo; however, no IP address was assigned on the Mac (the Lenovo said it had assigned 192.168.1.3 to the Mac). – BlueDevil – 2009-09-17T17:10:15.917

Answers

If you're running a Snow Leopard Server, you'll need to go to Server Preferences and disable the security firewall so that the computer can access the DHCP on the router. Once that happens, you'll be assigned the correct IP address.

This took me several days and hours to figure this out. It's so frustrating since I don't know if this security feature is overkill if you're behind a NAT router.

New to Mac OSx Server

Posted 2009-09-17T16:22:55.933

Reputation:

Does that business even use DHCP? If it is a "business grade" network, they may have specific network settings, MAC authentication, or other security measures along with DHCP. They do this to keep their machines on the network and others off of it. I assume you are authorized to use this network? You may have to obtain permission to add/use another computer on thier network.

Troggy

Posted 2009-09-17T16:22:55.933

Reputation: 10 191

1Good point -- BlueDevil, you said you upgraded from Leopard. Was this laptop working on this wired network before the upgrade? – Doug Harris – 2009-09-17T16:28:02.757

1Yes, they use DHCP with no other specific network settings. I have tried several other computers not native to the network and they all obtain IP addresses without issue including Linux and Windows OSs running in VMs. – BlueDevil – 2009-09-17T16:28:50.087

Yes. The laptop had no issues previous to the upgrade. – BlueDevil – 2009-09-17T16:29:55.217

2Does the MBP connect to other DHCP networks just fine or is this one the only problem? – Troggy – 2009-09-17T16:31:16.760

No, this appears to be an issue with the MacBook obtaining a DHCP lease in general. – BlueDevil – 2009-09-17T17:11:11.077

1Hmm, after reading your comment above, I am starting to wonder if the drivers or something isn't working right on the OS end. You might have to reinstall SL if you have no luck with anything else. Does the wireless connectivity connect to things ok? – Troggy – 2009-09-17T17:39:11.363

Yes. The wireless works great in all aspects including a self-hosted Ad-Hoc network and connecting to DHCP networks. Any ideas on the best way to reinstall the drivers without a full SL install? – BlueDevil – 2009-09-17T17:42:12.247

On my unibody MacBook Pro 17" running Snow Leopard, the DHCP problem turned out to be fixed by switching from WEP to WPA2 security on the WiFi network. I had no problem using it with WEP on an iPad, two iPhones, and another MacBook Pro (unibody 13"). In fact, both MBP's are running 10.6.8 so I'm still not sure why one worked and one didn't, but after switching to WPA2 everybody's happy!

Kent S

Posted 2009-09-17T16:22:55.933

Reputation: 11

Obvious answer: Have you confirmed that the ethernet port is configured to get IP address via DHCP?

If DHCP is already set for this network inteface, go to the "advanced..." window and click "Renew DHCP Lease". Does this help?

Ugly hack workaround: Delete the ethernet network interface (select it and click the "-" button at the bottom). Create a new ethernet network interface.

Doug Harris

Posted 2009-09-17T16:22:55.933

Reputation: 23 578

1I have already tried all of these solutions including restarting the computer, deleting the ethernet connection, and manually renewing the IP address. The laptop is still self-assigning IPs. Thanks for the suggestions. – BlueDevil – 2009-09-17T16:31:40.207

Have you tried repairing disk permissions and repairing the disk via disk utility from a bootable OS cd? A lot of times flakey permissions can cause all kinds of weird problems, especially after an upgrade.

MDMarra

Posted 2009-09-17T16:22:55.933

Reputation: 19 580

By running the following command on the MAC while attempting to DHCP one may provide more information (possibly than desired)

sudo tcpdump -vv -ien0 port 67 and port 68

user18567

Posted 2009-09-17T16:22:55.933

Reputation:

Probably not going to solve the problem because the test DHCP server shows assignment (2nd comment in question). – benc – 2009-12-21T18:30:47.070

If you're running ipfw, then add this line:

allow udp from 192.168.178.0/24 67,68 to any 67,68 in keep-state

Reiner

Posted 2009-09-17T16:22:55.933

Reputation: 1

I had the same issue after upgrading from Leopard to Snow Leopard. Upgrading SL from 10.6 to 10.6.1 resolved it for me, but YMMV

Rob Cowell

Posted 2009-09-17T16:22:55.933

Reputation: 1 273

My answer to this other question (for Wifi, but still applicable to your issue) will clear out your network preferences, which will be much easier than reinstalling the OS.

Problem with Macbook air automatically not acquiring free wifi network dns or router address

When I wrote that 10.6.2 wasn't out, but again reinstalling the 10.6.2 combo updater would be a great step to take before an OS reinstall.

ridogi

Posted 2009-09-17T16:22:55.933

Reputation: 2 787

We had a similar problem on our office network after we upgraded the DHCP (Debian Linux) host. Turned out the default /etc/hosts file on that box had a wrong entry for its own IP:

127.0.1.1 ns.ournetwork.nl ns

This IP was returned in the BOOTP/DHCP request, and Mac clients refuse this reply! Changing the IP:

192.168.1.6 ns.ournetwork.nl ns

and restarting dhcpd3 fixed the problem :-)

Lucson

Posted 2009-09-17T16:22:55.933

Reputation: