As this forum is viewed by more than a couple of people and I had the same issue with my Macbook pro yesterday, I thought I just share my solution with you. Note: the solution is general and not only for a Macbook (pro/air). So you can also use this guide for your Mac pro, iMac, G1, G2, G3, G4, G5 or Intel based Mac!
It could be that the settings are at different tabs when you are using another version of OS X than 10.5.4, just search for the right settings to set up as discribed below)
I always thought that if the LED on your router/switch is burning, the cable is good and your network card is okay. When it is not burning, that means your cable is not well connected, broken or your network card is broken. So that is why it scared the hell out of me when the LED wasn't burning when I plugged in my Macbook. (after being connected by cable the entire day) This just means your router/switch or your computer has turned the connection down by software. (Even in your preference panel > network setting > ethernet has a nice red light icon with "not connected" next to it. My eyes turned wet and red, but I knew there must me a solution for this, other than a broken network card on my Macbook pro.
The solution:
In short: your router/switch/modem has an identity problem. The DHCP server is screwed up and that's why you don't get a connection. (that is the reasen that Airport was working, but the ethernet wasn't)
If you don't know that DHCP means. No worries, read the following:
1) Doublecheck you have the cable connected in the right way
2) Turn off all devices that are connected with your network. And I mean all! (Internet modem, router, switches, airports, wireless bridges, computers, PS3, XBOX, etc. etc.
3) Leave them off for a minute
4) Turn them all on.
5) The problem could be fixed now, but no worries if it still isn't.
6) Go to your System Preferences > Network > Ethernet
7) Set Configure to Manually
-- Now you get a quick lesson in setting up fixed IP --
Image link:
http://img7.imageshack.us/i/picture2hb.png/
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8) The IP address you have to set could be very different than my settings, to find out what the right settins are, go to the Airport settings and check the tab "TCP/IP" and "DNS". (see the screenshots I've uploaded)
-- At the Airport settings --
Image link:
http://img205.imageshack.us/i/picture3zn.png/
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9) The IP set at IPv4 Address (where mine is 192.168.100.106) means that your Airport has set to this IP. So no other device in the network can use this IP at the moment. Because the Airport settings are on DHCP, it means that you cannot use a range of IP's. This range is mostly from XXX.XXX.XXX.100 to XXX.XXX.XXX.200 or 300.
This means the IP you have to use for your Ethernet must not be in this range. Else you won't get connected because your router and your computer try to be in the same place at the same time.
10) Write down the Subnet Mask number. In most cases it is: 255.255.255.0. If this number is different, just write it down, you have to put in the SAME number at the Subnet Mask for your Ethernet.
11) Router: 192.168.100.1 means the IP of my router is set at this number. You also have to copy this address to set this exact IP for your Ethernet.
--- Airport DNS settings ---
Image link:
http://img248.imageshack.us/i/picture4dt.png/
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12) Go on to the tab DNS in your Airport settings.
13) DNS servers are different for each Internet provider in the whole world. Just write down these two DNS numbers and the Search Domains if available. (DNS must be available anyhow)
14) close these tabs and go to your Ethernet settings
-- Ethernet settings --
15) Okay, now you have to fill in an IP Address that is NOT in the range of your Airport. BUT!!! The first nine numbers must be the same. So in my case the IP must be somewhere in the range of 192.168.100.2 and 192.168.100.99. Remember my router is at 192.168.100.1 so that one is taken and the Airport has taken 192.168.100.100 to 192.168.100.200.
I took 192.168.100.88. But if your router IP is (for example) 192.168.1.1 you have to use the 192.168.1.XXX range. And for XXX you have to type in a number. (nobody said this would be easy ;-))
Subnet Mask: just copy the IP from YOUR Aiport settings. Mine is: 255.255.255.0
Router: also copy the IP from YOUR Airport settings. Mine is: 192.168.100.1
DNS server: also copy YOUR settings (mine is 213.46.228.196) (the other IP address is a secundairy address in case one server isn't working. You could also use the other address without problems.
Search Domains: also copy YOUR settings (my settings are "arnhem.chello.nl", or 62.179.104.196, that depends on your settings at the DNS tab at the Aiport settings)
802.1X: Eduroam: forget this setting, that is something else, not of use for solving the ethernet problems.
16) Click apply and your Ethernet should be working again!
-- A short FAQ --
Q: My ethernet is still not working, what did I do wrong?
A: Pull out all the ethernet cables of your other devices at your modem/router. So your setup is only: internet modem > router > computer OR internet modem > computer OR AT MOST internet modem > router > switch > computer.
Q: OSX says the IP is already taken. What should I do?
A: Take another IP address for your ethernet. Be sure your IP address starts with the same nine digits as your router is! For example: Your router address is 192.168.44.1 you have to take an IP in the range from 192.168.44.2 to 192.168.44.300. If for example 192.168.44.50 didn't work out, try 192.168.44.150 or 192.168.44.250.
Q: Why didn't the guys from Apple or my Internet provider didn't tell me this.
A: Most people at a service desk don't know this kind of stuff.
Q: My ethernet is still not working?
A: Please make screenshots and/or ask on this forum.
A2: Try to connect your computer via ethernet on an entirely different network. At your friends house for example. Try the automatic settings unless your friend has the exact same internet provider!
Q: I still want my settings to be set at automatically, is this possible?
A: Just wait for a day or so and in most cases your crazy router has turned to normal again and you should be able to use the automatic settings again.
A2: If the problem remains you should reset your router to factory settings. If the problem still exists reset your modem to factory default. If the problem stillll exists just buy a new router.
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Hope you can solve the problem. In most cases your computer is working well and the ethernet card is NOT broken!!
