Ethernet port keeps getting self-assigned IP address and wont' connect to internet.

Discussion in 'Mac Basics and Help' started by DramaLLama, Dec 19, 2013.

  1. DramaLLama macrumors 6502

    Feb 6, 2011
    Wireless works just fine and I have rebooted my modem and router enough times for it to fix itself if that was the issue so I don't think it is. It was working a few weeks ago at someone else's house but at mine it's not working. Is there some setting that may have changed or is it an issue with my internet connection from my ISP?

    OS X 10.9.1
    Early 2011 13" MBP
  2. chown33 macrumors 604

    Aug 9, 2009
    on the Western Slopes, with E. A. Poe
    I'd try a different Ethernet cable, connected directly from your router to your Mac. If it works, then the cable you were using is bad, or one of the connectors is bad.

    If the different cable doesn't work, make sure your router has ethernet enabled. Also try the different cable with a different computer.
  3. DramaLLama thread starter macrumors 6502

    Feb 6, 2011
    Unfortunately I won't be able to get my hands on another cable until this weekend and won't be able to test it out until Tuesday.

    Right now the cable is providing internet to my router from the modem.. and wireless is working fine so would that mean the cable is working fine? When I disconnect the cable from the router and plug it into my computer is when I'm having issues.
  4. chown33, Dec 19, 2013
    Last edited: Dec 19, 2013

    chown33 macrumors 604

    Aug 9, 2009
    on the Western Slopes, with E. A. Poe
    It does.

    I don't entirely understand what you've done here.

    Which of these is correct:
    1. You disconnected the cable end-point attached to the router, and plugged it into your Mac.
    2. You disconnected the cable end-point attached to the modem, and plugged it into your Mac.

    If #1 doesn't work, there could be any number of reasons.

    One is that your modem is a cable-modem, and your cable ISP requires a single MAC address for that cable connection. My cable provided does this, for example. When I switched routers, I had to configure the new router to use the same MAC address as the old one. Your Mac has its own unique MAC address, so if the ISP is MAC-specific, your Mac won't be assigned an address.

    It's also possible that your ISP doesn't support DHCP on the modem (I'm assuming you have your Mac's ethernet port set to DHCP). Hard to say more without knowing about the service provider, the modem, and possibly the router.

    If you did #2, then I wouldn't expect that to work at all. However, this could depend on the specific model of the modem and the router.
  5. DramaLLama thread starter macrumors 6502

    Feb 6, 2011
    1 is correct. I disconnected the ethernet from the back of my router and plugged it into my mac... so it goes from my modem to my mac.

    My ISP is TWC (Time Warner). Modem is Motorola SURFboard SB5101 and my router is a Netgear WNDR3700 v.1 with firmware V1.0.16.98NA

    edit: and yes my ethernet port is set to DHCP. Whether or not my ISP requires a single MAC address I'm not sure but it shouldn't matter for the reasons I'm asking. This question was brought on by the fact that when I try and configure my router via ethernet instead of over wireless, it will not bring up the router page even though I'd be directly connected to it.. not trying to access the internet, just trying to configure the router itself. But either way I try and connect (to router via ethernet or modem via ethernet) my Mac won't recognize a connection.

    I phrased the OP asking about ethernet and *internet* connection (instead of router configuration) because I figured it would be simpler.
  6. chown33 macrumors 604

    Aug 9, 2009
    on the Western Slopes, with E. A. Poe
    Connecting a Mac directly to a cable modem is a very different configuration than connecting a Mac to a router that's then connected to a cable modem.

    You should always describe exactly what configuration you have, and not worry about whether it's "simpler" or not at first. The problem is that an answer for one configuration may be completely inapplicable for a different configuration.

    When you connect your Mac to your router, using the single ethernet cable you have now, which port on the router are you connecting it to?

    Here are the tech specs for your router:

    According to that page, your router has 1 WAN port and 4 LAN ports. If you plug your Mac into the WAN port, it won't work. You have to plug into one of the LAN ports. So that's the first thing to check.

    Judging by this picture which comes directly from Netgear's website:
    I'd say the WAN port is the yellow one on the right, and the LAN ports are the group of 4.

    Just to clarify what to expect, when you connect the Mac directly to the router's ethernet using your single cable, the resulting absence of a router-to-modem connection will disable all internet access. Anything that requires actual internet access will fail.

    By breaking the connection between router and modem, you've essentially created a small isolated LAN (a Local-Area Network), which provides some wifi connections and 4 ethernet connections for local devices, but which is completely disconnected from the internet at large. This should be ok if all you're doing is trying to connect to the router's builtin web-page for doing configuration. But if something requires any internet connection at all, such as searching, etc. then that will fail.
  7. Alrescha macrumors 68020

    Jan 1, 2008
    Many cable modems bridge only the first MAC address they see. If you unplug your router and plug in your Mac, you may need to reboot your cable modem so it accepts the Mac's MAC address. You'll need to reboot it again if you switch back to your router.

  8. DramaLLama thread starter macrumors 6502

    Feb 6, 2011
    Well that was easy... I had been using the WAN port while connected to my mac to try and connect to the router page... yesterday I tried ethernet port 4 (LAN ports) and it didn't work at the time so I figured it was all just screwed up. I plugged it into port 1 this time and it worked... that solves my original problem so I thank you for that. Sorry for all the confusion.

    As for whether or not the internet actually works through my ethernet cable I see you guys saying to reboot the modem after connecting to my Mac. I do not have time right now but I will post back later if that also solves that issue when I get the time to test it out. (I thought I had done this before but maybe I kept switching the ethernet cable around too much on my router then to my mac, etc... so maybe I just confused it).
  9. satcomer macrumors 603


    Feb 19, 2008
    The Finger Lakes Region
    What most people get wrong is you can NOT just change devices that connect directly to the ISP modem because most all ISP use MAC ADRESS connection to the device connected to it.

    So a typical user to change devices behind an ISP modem with cutting power to the modem for about 15 seconds then turn it back on. This will cause the software at the ISP server to scan for a new MAC ADRESS.
  10. provetobe macrumors newbie

    Oct 30, 2014
    Ethernet Self-Assigned IP Address Mac osx 10.6.8

    My Ethernet stopped working but WiFi kept working. I tried all the fixes listed here. My friend told me to check the cable again. I un-pluged, re-pluged and moved the cable around in case there was an intermittently open wire. Sure enough moving the cable fixed it so I must get a new Ethernet cable to run from my router to my MacBook Pro. Three hours of chats with the cable company, deleting files, turning on and off equipment etc. all because of a bad cable.
  11. Altemose macrumors G3


    Mar 26, 2013
    Elkton, Maryland
    Good testimony of bad cables. Just so you know, this thread is almost a year old.

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