I have an interesting problem and I believe I may be halfway to understanding it but don’t know how to fix it. My home network has two routers. One is the main one and is in a cabinet so I do not have wifi enabled as the cabinet limits the range of the wifi. I have a second router placed elsewhere which runs my wifi. Currently Ethernet shows connected but no access To the internet. My guess is there is an issue with the iP address as the internet works on wifi with the Ethernet cable disconnected and slowly with it connected. With wifi off the Ethernet still doesn’t connect to internet even though shows green. I guess there is a conflict and would appreciate some advice. Thanks in advance
MacOS – Mac won’t connect to internet
ethernetinternetmacmacosNetwork
Related Solutions
Days later, I've finally figured it out. The com.apple.mDNSResponder.plist file located in /System/Library/LaunchDaemons/ was corrupted, and for some reason attempts to reset it were not being saved.
I copied this file from a macbook that was able to connect, and, since I'm using Lion, added in the option to allow appending search domains by inserting the line
<string>-AlwaysAppendSearchDomains</string>
in the following position:
<string>/usr/sbin/mDNSResponder</string>
<string>-AlwaysAppendSearchDomains</string>
<string>-launchd</string>
I then restarted the machine. This appeared to do the trick.
This could be caused by Path MTU Discovery.
Test by changing MTU
To test this, go to System Preferences > Network
, click on Ethernet
then Advanced...
and finally select the Hardware
tab.
In there, you should see a Configure
option and the drop down menu next to it most likely is set to Automatic
. Choose Manual
then you'll see the other options become available. Leave all options as they are, but change the bottom one, MTU, from Standard (1500)
to Custom
and in the field that shows up below type 1400
.
Accept all changes and see if you have any more success while browsing.
Test using ping
in Terminal
A more definitive test you can do is in the Terminal.app and using the ping
command.
If the website that gives you trouble has a URL http://www.troublesomewebsite.com/, you can do the following:
- Ping the website by typing:
ping www.troublesomewebsite.com
. If you get responses, proceed to the next point below; if not, replace the www.troublesomewebsite.com with an address of another website you're having issues with and repeat. - When you find a site that does respond, type the following command and see if you get responses:
ping -s 1472 -D www.troublesomewebsite.com
. If you DO get responses, then it's NOT a Path MTU Discovery issue. - If you DON'T get responses, decrease the number 1472 to say 1464 and run the command again, like so:
ping -s 1464 -D www.troublesomewebsite.com
. Keep doing that until you start getting responses. Most likely, if this IS the PMTUd problem, you should get responses again with the packet size set to somewhere between 1464-1456 bytes. Add 28 to the number at which you start getting the responses and that's the MTU you can set on your computer to work around your issue.
Background Information
Path MTU discovery is a mechanism that manifests itself by frequent and seemingly intermittent timeouts when browsing some websites but not others. This has to do with misconfigured firewall rules on the website side, which prevent ICMP traffic to go through, specifically the ICMP unreachable
message. That in turn breaks the pmtud behaviour, which is how most of the TCP/IP stacks have been working for at least the last 20 years or so.
The MTU becomes an issue especially if your broadband connection uses DSL - in such case, there is an extra 8 bytes of PPP header that need to be used, and if the Service Provider didn't configure their links to use larger frames, this results in a smaller payload available to your packets - hence the need to decrease the MTU on your computer.
More information available in RFC1191 and this Wikipedia Article
Best Answer
Apple covers the basics in troubleshooting internet connections.
This is a nice resource since it is specific to several versions of macOS and if it’s too technical, you can refine your problem by working through it and asking a follow on question with details of where you got stuck or what sort of information doesn’t make sense.
Here’s the how to connect which also might help: https://support.apple.com/en-us/HT201735