After upgrading to Leopard, plenty of Mac OS X users have complained of “slow internet” when browsing the web, yet Windows PCs or Macs with Tiger (10.4) on the same network are much faster.
A domain name lookup or DNS lookup is done every time you visit a web page, say “apple.com”, as you’re actually visiting “17.149.160.49″. A DNS Resolver on your computer sends a request to a DNS Server that handles this lookup or translation from names (easy to remember) to numbers (hard to remember). Once your browser has this numerical IP address it can start loading the web pages at that server location.
With Leopard, a major change occurred in DNS lookups. Any program in Leopard that can use version 6 IP addresses will send out a new type of DNS lookup request - the SRV Record. In Tiger and previous OS X versions, DNS lookups were A record requests.
SRV records are fairly new, provide more information than A records, but have terrible support in terms of hardware (your router or cable modem) and DNS servers that answer with SRV information. For every SRV request that Leopard sends it must wait for a valid reply. If the request fails, Leopard must try again. If it fails again, Leopard will finally ask for an A record. This is one reason why Mac users are experiencing slow Internet on new Macs with Leopard or after upgrading to Leopard from Tiger.
Solutions
Add DNS servers to current Network Configuration
This is the quickest & easiest way to use new DNS servers, which is to simply add them to the DNS tab found in System Preferences => Network => Advanced => click on DNS tab.
Click on the + sign at the bottom left hand corner near IPv6 or IPv6 addresses and type in the addresses of the DNS servers you wish, in reverse priority order. (Recommended: OpenDNS servers at 208.67.220.220 and 208.67.222.222). I.e. the server that you want to use first, enter it last. Afterwards, click Ok. Then in the Network pane, click Apply to make your changes active. If you’re using an AirPort wireless connection, wait a few moments for the connection to be re-established
Or You Could
Disable IPV6 DNS lookup
Firefox and Camino by default do DNS lookups using IPv6 addresses by default, reverting to IPv4 if that fails. This can be a problem when the router that we are using to connect to the Internet doesn’t work with IPv6 DNS requests properly, if at all.
To disable IPv6 DNS lookups in Firefox and Camino, type the following into the browser address bar:about:config
If you see a large “Be Careful” warning, simply click on “I understand and I wish to continue”. Next, you will see a long list of Preference Name, Status, Type and Value columns. Above all that is a bar in which you can filter which preferences to view. In the Filter bar type: ipv6
To change the value for this preference simply double-click the name “network.dns.disableIPv6″. The value you want is “true”, which means that IPv6 DNS requests are disabled. If this value is already “true”, don’t double-click this preference.
To make the preference change active, close the browser and Quit Firefox completely (Apple Key + Q), then restart Firefox. You may have to repeat this Quitting and Restarting to have the change take effect.
After making this change, Firefox (or Camino if that’s what you’re using) will use IPv4 only when performing DNS requests.
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