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Can't Share Internet Connection

My iMac is connected to the internet via a wi-fi modem/router. I have had a Mac Pro and an internet-enabled (for captions) telephone connected to the iMac via an ethernet splitter, and each has had a perfect internet connection for months. All I ever did to make it work was turn on Internet Sharing in the the Sharing Pane of System Preferences on the iMac.


I've now retired the Mac Pro and have connected the phone directly to the iMac and just noticed that it doesn't have an internet connection. The reason is that, in the Network Pane of System Preferences, I see "Ethernet has a self-assigned IP address and will not be able to connect to the Internet."


I've restarted the router, the iMac and the telephone but always ethernet gets a self-assigned IP address, and the phone doesn't see an internet connection. I also reinserted the ethernet splitter between the iMac and the phone but that made no difference and I've removed it again.


Does anyone have any idea why this has suddenly broken after working for months and, more importantly, how to fix it?

Thanks in advance,

Steve = : ^ )

iMac, macOS Sierra (10.12.1), Windows XP & 8.1 in Parallels 12

Posted on Dec 2, 2016 9:38 PM

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Dec 11, 2016 4:43 PM in response to Erroll

I'm replying to this to bump it up in the hope that someone more knowledgeable than me missed it. This is an important issue for me as I can't talk on the phone without captions and my phone isn't getting get any DHCP information and can't contact the captions server. It used to work perfectly.


In Network/Ethernet/Advanced I can renew the DHCP lease but the address obtained doesn't resemble addresses given out by my router, and is obviously being assigned by the Mac. Why?


When you turn on Internet Sharing, does the Mac poll the router to assign another IP address? Share its own IP address? What, exactly, is broken here?


Thanks in advance,

Steve = : ^ )

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Dec 12, 2016 7:36 AM in response to Erroll

Please refer to macOS Sierra: Share the Internet connection on your Mac.


From what you describe, it seems your iMac's Network Service Order is not configured the way you would like it to work. If you want your phone to share the network connection provided by your iMac, the iMac must connect via Wi-Fi. To fix that, open Network Preferences, click the "gear" icon, then Set Service Order...


Drag Wi-Fi anywhere above Ethernet. Click OK then Apply. The iMac will connect to the network using Wi-Fi, and that connection will be made available to other devices over its Ethernet port.


If the phone is the only one device connected to the iMac's Ethernet port, you won't need the splitter.


More detailed instructions can be found in https://help.apple.com/machelp/mac/10.12/index.html?localePath=en.lproj#/mchlp15 40. The relevant description can be found in Steps 3 and 4.

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Dec 12, 2016 1:21 PM in response to John Galt

John Galt wrote:


Please refer to macOS Sierra: Share the Internet connection on your Mac.



Thanks for the reply. I set up Internet Sharing over a year ago and it has been working fine until recently.


From what you describe, it seems your iMac's Network Service Order is not configured the way you would like it to work. If you want your phone to share the network connection provided by your iMac, the iMac must connect via Wi-Fi. To fix that, open Network Preferences, click the "gear" icon, then Set Service Order...


Drag Wi-Fi anywhere above Ethernet. Click OK then Apply. The iMac will connect to the network using Wi-Fi, and that connection will be made available to other devices over its Ethernet port.


Here are my settings. What would you like me to change?

User uploaded file

User uploaded file

User uploaded file

Thanks again,

Steve = : ^ )

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Dec 12, 2016 2:02 PM in response to Erroll

Hi Steve,


All that looks completely normal... unfortunately.


I duplicated the same setup on an iMac and it looks like yours:


User uploaded file


The other end of the Ethernet cable is connected to another Mac. Its Network preferences looks like this


User uploaded file


The Ethernet address shown in Internet Preferences on your iMac is not important. It is normal for it to indicate "self-assigned IP address" because it's not connected to the Internet. What I would need to know is how your phone connects to the Internet, and how it is receiving an IP address (because apparently, it isn't).


As far as I can tell your iMac's settings are correct.

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Dec 12, 2016 2:15 PM in response to Erroll

Yes.


There are only two IP addresses that matter: the one assigned to your Mac by the router it's using, and the one it assigns to the phone. I am nearly certain they will be using different subnets and that's how it must work.


Apparently the iMac distributes IP addresses in the 192.168.2.x range. As you can see it assigns itself 192.168.2.1 and the one pulled by the Mac via "sharing" reports its IP address is 192.168.2.2. That's how it should work.


Since your phone does not appear to be connected to anything, that's the place to look. How can you do that?

The obvious solution would be to connect your IP phone directly to your router. I realize that may not be convenient for you, but that's probably how it's supposed to work.

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Dec 12, 2016 2:14 PM in response to John Galt

Ah, thanks. I was confused by "will not be able to connect to the internet". Despite that message, with Internet Sharing enabled, a device connected to the Ethernet port should still be able to connect to the internet. I can now stop trying to fix the "self-assigned IP" on the iMac's Ethernet.


Unfortunately, my internet-enabled phone does show me network settings. It just goes out and gets DHCP information and finds the captions server – when it's all working, which it has been.


Now it's failing to to get an IP address from the DHCP server, which I guess is my router.


The phone also has wi-fi, but it's a nuisance as it disconnects when the phone's not used for as while and I have to reconnect whenever I want to make or receive a call. However, it does connect. It confirms making a connection with the DHCP server, getting an address and then connecting to the captions server, so my router's not the problem.


AS far as I can tell, the problem is that, despite what it says in the Sharing preferences pane, my iMac isn't sharing its internet connection.


Thanks again,

Steve = : ^ )

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Dec 12, 2016 2:28 PM in response to Erroll

Despite that message, with Internet Sharing enabled, a device connected to the Ethernet port should still be able to connect to the internet. I can now stop trying to fix the "self-assigned IP" on the iMac's Ethernet.


Yes. I agree. The iMac is not the place to look, besides, what you can see on it all appears to be normal.


Now it's failing to to get an IP address from the DHCP server, which I guess is my router.


Yes. Actually, it would be getting it from your iMac, and it will probably be in the range 192.168.2.x.


If there is a way to determine the addresses the iMac is actually distributing to its Ethernet clients, I'll try to find out what it is.

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Dec 12, 2016 3:22 PM in response to John Galt

Thanks, but I may have found it. I have a Time Capsule in bridge mode (wi-fi disabled) and connected to the iMac via Ethernet (for Time Machine backups). The phone is currently connected through the Time Capsule but I've tried it with the phone connected directly to the iMac and it makes no difference so I haven't mentioned the Time Capsule.


I just realised that I can use Airport Utility to look into the Time Capsule.

User uploaded file

So it does see the iMac as its router with the address 192.168.2.1. (I entered those DNS server address myself. There were different ones there – left over from when I was using the Time Capsule as a router. I don't think they mean anything in bridge mode.)

User uploaded file

If I hover over that 'Internet Connection' it tells me that the Airport base station doesn't have a valid IP address and make sure it's connected to my broadband modem (it's not) or my local network (it is, the iMac).


So this seems to document the same problem that the phone displays: the iMac is being seen as a router by Ethernet-connected devices, but it isn't handing out IP addresses.


Why not?


Steve = : ^ )

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Dec 12, 2016 3:55 PM in response to Erroll

That does complicate matters. If you are using a combination modem / wireless router, all your devices should be clients of it. That means you should connect your TC to that network wirelessly, or directly to it using an Ethernet cable assuming your modem / router has one. Either one of those connections is going to require that you reset the TC and reconfigure it using AirPort Utility.


The reset will not affect your existing backups, but you will need to "reconnect" to it so that backups can resume.


Your existing configuration can probably be made to work, but it seems needlessly complicated whereas a network should be constructed to be as simple as possible.


A picture would help, but an overly simplified description should look like this:


ISP --> Modem --> router --> Ethernet switch --> all wired devices


Wireless devices should be connected wirelessly to your combination modem / router / wireless access point, and not through something else.


Connecting a wired network device (such as your TC) to a wireless Mac's Ethernet port, and then effectively using the TC as a switch for more wired devices bridged using the Mac's Internet Sharing feature... yes, that can work, but thinking about it gives me a headache.

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Dec 12, 2016 4:46 PM in response to John Galt

I used to have the TC connected to the modem/router but that meant Time Machine backup and restore happened over wi-fi (the cable outlet is nowhere near my computer). I recently had cause to restore this whole computer from a backup and it took eight hours over Ethernet. I shudder to think what it would take over wi-fi.


I don't believe it's an issue: the TC is in bridge mode (router disabled) and the wi-fi is disabled. It just functions as an Ethernet disk. Plus, I had the phone and a Mac Pro connected via an Ethernet splitter and it worked fine for months. It just had eight equivalent ports – no 'In' or Out' – and I assume the three LAN ports on the TC will function the same way, but to simplify things, here's what I just did:


  • disconnected and powered down the TC
  • connected the phone directly to the iMac and powered the phone down
  • shut down the iMac
  • powered down the modem/router
  • booted the modem/router and waited till it had a WAN connection
  • booted the iMac and waited till it had a wi-fi internet connection
  • verified that Internet Sharing from Wi-Fi to Ethernet was on
  • booted the phone

The phone failed to connect to the internet with 'DHCP Service Failed'. This is exactly how it's been since I first posted. Unfortunately, the phone won't let me investigate further so I ...


  • disconnected the phone and connected the TC in its place
  • booted the TC
  • started AirPort Utility


AirPort Utility gave exactly the same reports as I pasted above. The TC (and, presumably, the phone) sees a router (the iMac) at 192.168.2.1 but the TC (and presumably the phone) doesn't get a valid IP address. That's the problem.


This is no issue for the TC because it doesn't need to connect to the internet, but it breaks the captions on my phone.


Thanks,

Steve = : ^ )

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Dec 12, 2016 5:03 PM in response to Erroll

I hate this! Somewhere in all the patching and re-patching, disabling and re-enabling, shutting down and re-booting, it has started to work – and with the TC between to iMac and the phone, no less! And I've been trouble shooting this, off and on for days. Arrrggghhh! I have zero idea what fixed it. 😕


Many, many thanks for all your efforts. 🙂


Steve = : ^ )

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Can't Share Internet Connection

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