Ethernet is active but no internet connection (although Wi-fi works)

Pluistronaut · Mar 6, 2012

Hello everyone,

As of this morning, the wired internet connection on my iMac stopped working. A little background info:
I live in a student complex in the Netherlands where the internet connection enters my apartment with just an ethernet cable (no modem). This cable is connected to a TP-Link switch (type: TL-SG1005D). From here, a Cat 5E cable runs to my iMac.
This configuration has always worked, just until this morning. The network preferences pane gives me the following info:

Ethernet is currently active and has the ip address 169.254....
Subnet mask: 255.255.0.0
Router: (nothing) ---> there used to be an address here but it is gone now

Strange thing is that I also have an Airport Express connected to the switch which does have an internet connection (I am typing this message from a MacBook pro connected to this Airport Express).

After looking all over the internet for solutions, I have tried the following:

-reset the switch
-reset the iMac
-unplugged/plugged the ethernet cables back in
-tried different cables/ports on the switch
-renewed DHCP lease
-created another network location, added ethernet adapter, renewed DHCP lease

As I do have a wireless connection with my laptop and the ethernet cable does not give me a connection on the laptop, I think the problem lies with the switch. It couldn't have anything to do with the ISP, as I can connect to the internet wirelessly, right?
I read that the 169.xxx IP address means that it is a self-assigned IP address.
Maybe the distribution of IP addresses by the switch doesn't work anymore, and the Airport Express distributes its own IP addresses to the wireless devices, enabling me to access the internet through wi-fi?

Thanks for the help!

sfam198 · Mar 10, 2012

Switches, like the one you are using, do not assign IP addresses. The are assigned by DHCP servers, which in consumer grade network equipment are usually built into routers like your Airport Express. The student complex where you live also would have a router or separate DHCP server somewhere on its network.

Just so I understand your setup correctly, I'm assuming the following:

1. You have a wall jack (or just a cable from the wall) for network access (technically it's not just Internet access)
2. You plug an Ethernet cable into that wall jack and connect it to your 5-port switch (the TP-Link)
3. You have an Airport Express plugged into a port on the TP-Link switch
4. Your iMac is plugged into a port on the TP-Link switch with an Ethernet cable

So, you say that devices connected wirelessly to the Airport Express can access the network (and the Internet). So that rules out a bad network connection in the wall. It also rules out a bad Ethernet cable from the wall to the switch, as well as a bad cable from the switch to the Airport Express.

The first step I would take is to plug the Macbook Pro into the network with the Ethernet cable you are using with your iMac. If it works, you know the problem lies with your iMac itself, not the network equipment. It it doesn't work, take all the network equipment out of the equation and plug into the wall port (or cable) directly. If that works, start adding one piece of equipment at a time until it doesn't work again. The piece that breaks the chain is your culprit.

englishman_ph · Mar 14, 2012

...are you able to go inside the modem (tp-link) page?
...you might also need to ask you "roomies" if they are experiencing the same issue
... if the answer is "yes" its possible ISP issue

just sharing some basic knowledge :Smirk:

MrMonoboy · Nov 3, 2012

Having the same issue

I'm having the same issue. Wi-fi working perfectly, Ethernet connected but no internet access. Tried restarting iMac, router, deleting network prefs and starting again, renewing the DHCP lease, nothing works.

Using a standard router via TP-Link adapters. All working perfectly until today. I also have an old Macbook Pro which connects via same ethernet cable without any issues. Most definitely my iMac.

Automatically configuring via IPv6, all with different IP addresses. To add to this, my iPhone (4, iOS6) has occasionally dropped the Wi-fi connection in the past.

Seriously flakeyness going on. Anybody have any pointers on diagnostics? I tried the Network Utility but have no idea what I'm looking for.

Thanks.

Ethernet is active but no internet connection (although Wi-fi works)

Pluistronaut

sfam198

englishman_ph

MrMonoboy

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