5. Reset your router
For network problems that lie beyond your Mac, if you own or control the network device your Mac connects to (such as an AirPort base station, Time Capsule, router, switch, or hub), turn that device off, wait about 10 seconds, and turn it back on again. Wait for it to power on completely (sometimes a multistep process that can take several minutes) and try connecting again.
If there's more than one such device between you and the Internet--for example, an AirPort Express connected to a cable modem--start with the one closest to the Internet and then work your way back to your Mac, cycling the power on each one as you go.
6. Check your DNS settings
The Domain Name System (DNS) enables your Mac to convert domain names (like apple.com) into IP addresses (like 184.108.40.206). If the DNS server your Mac uses is offline, slow, or faulty, you may be unable to connect to any site or service by name. Here's an easy way to check whether DNS is functional if no websites, such as google.com, respond. In your browser, type in this URL: http://220.127.116.11. That should bring up the Google website. If it does, then you know your Internet connection itself is fine and the problem is merely looking up domain names.
To fix that problem, open the Network pane of System Preferences and select your network connection in the list on the left. Click Advanced followed by DNS. In the DNS Servers field, you should see one or more IP addresses. If those addresses are enabled (black, as opposed to gray), select each one in turn and click the minus-sign (-) button. Then, regardless of whether there are already addresses there in gray, click the plus-sign (+) button and enter 18.104.22.168; repeat with 22.214.171.124. (These addresses point to OpenDNS, a free DNS service that's often more reliable than the default servers your ISP uses.) Click OK and then click Apply. Now try connecting again.
Getting back online
Even after following all these steps, success isn't guaranteed, because some outages could be beyond your control. Because of the distributed nature of the Internet, an equipment failure at an ISP can affect more than just that ISP's customers. And on a larger scale, accidental damage to a major fiber optic cable can (and occasionally does) wipe out Internet access to a large region. So, sometimes the only solution to an Internet outage is to wait for it to be fixed. But if the problem lies beyond your local network, your ISP should at least be able to tell you the nature of the problem and an expected repair time.
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