6. Network diagnostics
Your Mac has a built-in tool for diagnosing connection problems, but, like many of OS X's useful tools, it's tucked away. To access it, click System Preferences in the Apple menu and click on the Network pane. At the bottom of the window, click Assist Me. On the next dialog box, click Diagnostics. You'll now be taken through a series of steps; the first will ask you to choose how you connect to the network. If you choose Wi-Fi, you'll then be asked to choose which wifi network you want to connect to. The utility will then perform a series of tests to try and identify where the problem lies. Sometimes it will be able to fix it, on other occasions it will tell you where the problem is, but won't be able to resolve it.
If none of 1-6, above, work, it's worth changing the Domain Name Server (DNS) settings. The DNS settings dictate where your Mac or iOS device goes to look up a URL and turn it into an IP address. If there's a problem with the DNS server, it won't be able to resolve URLs and so your Mac won't know where to go to find a website or online service. If you've never changed DNS settings, they'll be set at the the default used by your ISP. And so if your ISP has DNS issues, you'll have connection problems.
To test whether you have a DNS problem, open a web browser and type http://22.214.171.124/ into its address bar. That should take you to google.com. If it does, and you can't access Google by typing 'google.com' into the address bar, it's a DNS problem.
To fix it on your Mac, go to the Network pane in System Preferences again. Click Advanced, then click the DNS tab. Click on each of the servers in the left hand window and click the '-' button at the bottom. Now replace them with either DNS servers run by Open DNS (126.96.36.199 and 188.8.131.52) or Google (184.108.40.206 and 220.127.116.11). Both are free to use and very robust.
You can do the same on an iOS device by going to Settings, then Wi-Fi and clicking on the 'i' next to your wifi network. Then type the new DNS server address.
8. If some sites work but others don't
Occasionally connection issues crop up with several websites, but not all. On these occasions, out of date cached files may be to blame. The solution is to flush the browser's cache. The method will depend on your browser. In Safari 8, go to the Safari menu and select Clear History and Website Data, then choose 'all history' from the menu. Note that this will delete your History on the Mac, and, if it's signed into your iCloud account, all other devices signed into that account.
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