After the computer starts up, you should enter a valid DNS server address in the Network pane of System Preferences. You may add more than one DNS server address, ensuring your service in the event that one becomes unavailable. If you do not know your DNS server address, get it from your network administrator or Internet service provider before continuing. Only they can provide you with this information. If you already have correct DNS configuration, be sure that the network interface, or "port", that you use to connect to the Internet is listed first in your Active Network Ports list. Examples of network interfaces are Built-in Ethernet, AirPort, and Internal Modem. Mac OS X searches the ports in the order that they are listed.
These steps cover both the DNS and port priority aspects:
- 1. Choose System Preferences from the Apple menu.
2. Choose Network from the View menu.
3. From the Show menu, choose the network interface you use to physically connect to the Internet. See Note 1.
4. Click the TCP/IP tab.
5. Type your DNS address in the Domain Name Servers field. If you have more than one, press Return at the end of each to put the next address on a new line.
6. Choose Active Network Ports from the Show menu. See Note 2.
7. If the interface you chose in Step 3 is not at the top of the list, drag it to the top. See Note 3.
8. Click Apply Now.
You may need to quit and reopen some Internet applications to return to normal behavior. If you still have a connection issue, more general information is available from Mac OS X: Internet and Network Topics (Getting Connected, Troubleshooting).
Users of portable computers may need to prioritize different network interfaces for each place that they use their computers. You may, for example, prefer Internal Modem when at home but AirPort when at work or school. If this is your case, you may wish to read more about the Location menu. See Mac OS X: How to Use Locations.
A DNS server converts DNS names, like "www.apple.com" into their IP address equivalents, such as "220.127.116.11". When you do not have DNS service, your computer cannot find the IP address of the target server based on its DNS name. During startup, Mac OS X recognizes your otherwise valid Internet connection and then waits a predetermined amount of time for a DNS response before continuing, resulting in the longer startup time. This pause is known as a "timeout." If you encounter some applications that continue to work, it may be because they are set up to go directly to an IP address, bypassing the need for DNS service.
Some networks and Internet service providers use a protocol that allows your computer to discover DNS service automatically on the network without manually typing any DNS server addresses. This is why the Domain Name Servers field in System Preferences is labeled as optional. If your network provides automatic discovery, you should only encounter the symptoms if you have specified an incorrect DNS address, versus leaving the address field empty, which would not affect your computer. This means that valid troubleshooting steps include both:
- attempting to connect the the DNS field blank
- manually typing a valid DNS address, even if automatic discovery is provided