There are a few reasons why you may not see changes you make to your DNS right away. These processes are sometimes generally referred to as propagation, but these are the specific reasons.
1. TLD Zone Update Intervals
Some TLD zones do not update in real time. When you make a change to your nameserver listing in our control panel, we send the changes through to the registry almost instantly. However, every TLD is controlled by its own registry and the registry determines how often they update the nameserver records for each domain. For example for .com changes are updated in 3-5 minutes, whereas changes for .jp domains may take up to 24 hours.
2. ISP DNS Caching
To obtain addresses for web sites you visit, your Internet Service Provider (e.g., Comcast, Verizon) uses recursive and caching DNS servers. These servers store past lookups from users on their respective networks.
For example, if you use your computer to look up www.example.com in your browser, your ISP’s recursive DNS servers may go out and find the address 192.168.0.1. If you look up www.example.com five minutes later, the DNS servers won’t go through the trouble of looking up the address again, it will just remember the address from the lookup five minutes earlier. The process is called DNS caching and ISPs have been known to cache DNS lookups from 1 to 24 hours.
DNS caching may affect you when you change the DNS servers or host records on your domain. For example, you visit your domain and your ISP looks up the address and caches it for 1-24 hours. Then you go to your domain control panel, make a change to your nameservers or host records, and then visit your domain again. However, rather than looking up and finding new records, your ISP still responds with the cached records.
3. Your PC’s DNS Caching
On some rare occasions, the address may actually be cached by software on your PC. To “flush” any cached DNS records, please do the following:
From a command prompt, enter the following command:
For Mac OSX Leopard and above, enter the following command from a bash prompt:
For Mac OSX 10.5.1 and before, enter the following command from a bash prompt:
Restart the NSCD daemon by entering the following command from a bash prompt:
To determine if any of the above issues are affecting your domain, you can use a third-party online utility, such as IPTools. From there you can do a DNS Lookup on your domain name. Choose an A record lookup when prompted. If everything is working correctly, the returned A record should match what you have entered for the corresponding host record. If not, you may need to let 24 hours elapse to allow for propagation delay.