Why is my iMac not connecting to the internet

April 7, 2023 9:35 AM

iMac system preferences confirm that the device is connected to wifi and ethernet but still getting error message: "Not connected to internet"

Partner is reporting this issue, they work at a library/archives and this is one of a few workstations used. They have tried the following:
- disconnected the router, ethernet cable, power source, and restarted everything
- tried a few basic diagnostics (they've been a Mac user much longer than I have, and I can't begin to troubleshoot this on site let alone remotely)
- no luck with googling for suggestions so far

I will supply more info if anyone asks, and appreciate any ideas as to how to resolve this. Thank you for your time!

posted by elkevelvet to Technology (5 answers total)

Have the library's internet provider reset the router from their end. That would be one thing to try.

It's definitely possible to be connected to Wifi, or connected via Ethernet to a router, but not have an internet connection. The computer is telling you "I can see the local network I'm connected to, but that's it."
posted by emelenjr at 11:27 AM on April 7, 2023

I'm no specialist. My first thoughts are :

- the router is blocking that particular mac address (unique computer identifier) either automatically, or it was added to a block list manually (if other computers are on the same network or at the same ethernet port can connect to the internet). So maybe try connecting that ethernet cable into another computer to rule out that part of a hardware issue, or try connecting the iMac to a different network (physical or WiFi).

- the iMac has a virus running in the background, using the internet to send spam / viruses, etc but masking the main system from connecting, so as not to be able to download anti-virus or software updates (which may then block & remove the virus). I know viruses used to do this kind of thing, so I imagine they still do.
posted by many-things at 11:34 AM on April 7, 2023

i had a similar out the blue problem like this and it turned out the DNS settings on the mac had gone awry .. could be worth checking .. they should usually be pointed to your internet providers , but you can point them to googles

For IPv4: 8.8.8.8 and/or 8.8.4.4 .
For IPv6: 2001:4860:4860::8888 and/or 2001:4860:4860::8844 .

Settings -> Network - DNS tab
posted by burr1545 at 1:55 PM on April 7, 2023 [1 favorite]

Assuming there are a couple of other iMacs at the library that can connect to the internet, take a look at the settings on those machines and make sure the disconnected iMac are set-up similarly.

Also, this being a library, is there a security gateway the computers have to pass through first before they can hit the internet? Perhaps this misbehaving iMac isn’t seeing the gateway?
posted by Thorzdad at 5:06 PM on April 7, 2023

Best answer:

> tried a few basic diagnostics

Knowing more about this might help give more precisely targeted advice.

It sounds like this is a wired connection, so here's what I would check, in order:

1. Check the physical connection to the network (e.g. make sure the cable jack is firmly seated, scrutinize the ethernet cable for signs of damage (or test temporarily with a different cable if a physical layer problem is suspected.)
2. If you have access to the switch or router to which it connects, check to see whether that device believes it has a connection (e.g. is the link light corresponding to that port lit)
3. I would usually check at this point to see whether the interface is configured on the computer and enabled. Typically I'd use the command "ifconfig -a" in a terminal window, but if you don't know how to read ifconfig output you can check the Network control panel and see whether it believes the wired ethernet interface is enabled. By the way, is this a Mac old enough to have a hardwired ethernet port or is there is a USB-C dongle providing this ethernet jack?
4. If the router has a link light for this circuit and the computer believes its interface is enabled, I'd next try sending out ping packets using a known IP address. If you open a terminal window and type "ping 8.8.8.8" and you receive a sequence of lines saying things like "64 bytes from 8.8.8.8: icmp_seq=0" then you can conclude that (a) packets are leaving the local computer, transiting the network, and replies are being returned by a device outside the local area network" which would point to it likely being a DNS issue. If you don't get ICMP replies from 8.8.8.8 then I'd try to see whether you can either ping something like the local router gateway or I'd try a traceroute to see how far your packets get before dying - but those steps are a little more complex than I want to write right now so.. if you get to that fork and need more help, ask and I'll write more, but I think it's more likely you'll find you have misconfigured DNS..
5. If you can successfully ping an address outside the local area network (such as 8.8.8.8) and receive replies, but you are still having problems, then probably you are having name resolution issues. Try pinging something by domain name, rather than by IP address.. e.g. "ping www.google.com" If you are having name resolution issues, the most likely result is that you will get an error saying you can't ping because "unknown host", possibly after a delay where it tries to resolve the hostname, fails, and times out.

posted by Nerd of the North at 7:18 PM on April 8, 2023