If you installed Sierra and are facing Wi-Fi issues, it could just be that the name servers are set up wrongly. It is quite an easy fix as long as you know what you are doing. This post will talk about how you can go about fixing your Mac OS Sierra name servers.
To first access your name servers, go to settings in your Mac. Once there, choose the Wi-Fi connection that you actively use and then click on TCP/IP settings. Once in there, go to edit name servers.
Do not worry about editing these name servers and entering something that will risk the security of your Mac. The name servers that we are just about to give you are public name servers that are used by Google. They are extremely safe and in fact a lot of Mac users actually swap default Mac name servers with Google name servers, as it makes a Wi-Fi connection more robust and even faster at times.
In the fields that ask for DNS, enter 184.108.40.206 and 220.127.116.11 and then save your Wi-Fi settings. For good measure, please restart your Wi-Fi router as well. Don’t just quickly turn it off and on. Rather, turn off the Wi-Fi router and wait about 15 seconds and then turn it back on. Simultaneously, turn on your Mac as well.
This would have hopefully fixed your Mac OS Sierra W-Fi Problems. If not, it could be that your router is faulty. Have a friend come over with their phone or Mac and see if they are successfully able to connect to your problematic Wi-Fi connection. If they are, then it is a problem with your Mac and you can maybe contact Apple support.
Otherwise, you can possibly try changing your Wi-Fi router or try to reconfigure it using the CD that it came with. Please note that reconfiguring will mean that you will need the assistance of your ISP. So, have them on a call while you reconfigure it.
Hope these tips about fixing Wi-Fi problems on Mac OS Sierra really helped you. If you are facing Sierra running slow issues on top of your Wi-Fi problems, you can try the fixes mentioned in the resource link just given a few lines before.