Speed Up DNS Propagation by Ensuring DNS Cache is Purged
DNS Propagation Taking Too Long | DNS Replication Problems | How To Clear DNS Cache | DNS Troubleshooting | DNS Benchmarking | Changing DNS Provider
Modified DNS entries can take hours or even days to replicate across the internet. And often, this delay can be extended unnecessarily by old DNS cache residing on your computer and slow, Public DNS servers.
This article details the checks you should perform after updating DNS records to ensure that cached DNS lists and slow-to-refresh Public DNS servers are not misdirecting your browser and causing unwanted delays.
This article is useful in these circumstances:-
- Moving a web site from one host to another: When name servers or DNS records have been updated to point your domain to a new hosting company. The hosting company confirms that the DNS transfer is complete and that your site is working normally but your domain name still directs to your previous host and old website.
- Pointing a domain name to a website: When name servers and DNS records have been set to point your new domain name to your new web site. You are still waiting for DNS records to propagate throughout the world’s networks for your new web site domain name to be resolved.
- Troubleshooting a problem with DNS.
- Learning how to clear your DNS cache.
- Making browsing speed faster. You could benefit by changing your ISP’s default DNS servers.
- Benchmarking DNS servers in order to choose the one optimal for you.
What is DNS?
The Domain Name System (or Service or Server) is a look-up table that resolves internet web addresses like Facebook to their respective IP address, i.e. 220.127.116.11 – the backbone on which computers are able to connect and communicate.
Without a DNS directory, we would all have to remember meaningless numbers instead of easy-to-remember names.
When a web address is requested in a browser, it’s equivalent IP address is sought by these steps and in this order.
1. Local hosts File
On a Windows Operating System, the hosts file in:
is the first port of call. If the web address is recorded in that file with a corresponding IP address, then the browser will be directed and the search ends there.
2. Locally Cached DNS
If there is no record of that web address in the hosts file, then locally cached DNS is searched next. This can be stored on the computer itself and / or inside the router. If a suitable record exists in stored DNS cache, the search will conclude there and the browser will be directed to that stored IP address.
Some routers are capable of storing a cached copy of Domain Name System lists. If one does exist, this cache will be the next list to be searched to enable fast interpretation of the web address, instead of requesting that data from a Public DNS.
3. Public DNS
Only when the previous two steps cannot be fulfilled does the request go to a Public DNS to resolve the web address to an IP address.
How to Clear Cached DNS
Follow these steps to ensure that you are not waiting unnecessarily for DNS replication and propagation after updating DNS records and name servers of your website.
Check the hosts file
It is always worth checking your hosts file in notepad to see if there have been any redirects added in the past that you may have forgotten about – or indeed, not known about.
Tip! notepad has to be opened with Administrative privileges if you are going to make any changes to your hosts file.
If there is a reference in your hosts file to your problematic site, then make a back up of the file; remove that entry and save the hosts file. You may need to re-boot your computer for the new hosts file to be read by the operating system.
Clear Local DNS Cache
Open a command console with Administrative privileges by clicking on the Windows START icon (bottom left) and typing cmd into the search field. Do not press Enter.
cmd.exe will appear at the top of the list. Right click on it and select Run as administrator. The command console will open.
In the command console type:
and press Enter.
The console will report Successfully flushed the DNS Resolver Cache. Close the console window.
Check and Clear Router DNS Cache
Some routers are capable of caching DNS lists. You should determine whether or not your router does this and if it does, purge that list.
Log into your router and look for for an option or something that resembles Advanced DHCP Settings or DNS Settings.
The example shown below is of a NetGear router with the option to clear router DNS cache.
Change the Public DNS Primary and Secondary Addresses in your Router
By default, most routers are programmed to obtain and use your ISP’s Primary and Secondary DNS addresses automatically.
However, these servers could be slow to replicate changes in DNS records and therefore slow to propagate the changes you have made. They might be over loaded too, causing substantial look-up delays that decrease browsing speed.
There are many alternatives to DNS servers supplied by ISPs. The benefits of using an alternate provider include:-
- Faster refreshing of DNS record changes
- Faster browsing speeds
- Improved security
- Family filtering
Google Public DNS is a free Domain Name System that can be easily configured for use in your router without having to install any software. OpenDNS is another free Domain Name System that is commonly used.
To configure your router manually to use another Public DNS, log in to it and find an option similar to this: Domain Name Server (DNS) Address and select Use These DNS Servers. Enter the two IP addresses given by your chosen provider.
Save the changes if necessary then re-boot the router.
Once all these steps have been completed, try to access your domain again.
DNS Benchmark – Chosing a DNS Provider that is Optimal for you
The DNS Benchmark by Steve Gibson at the Gibson Research Corporation is a valuable tool for finding the DNS provider optimal for you. It is a free and small, stand-alone program that requires no installation. Try it and discover faster browsing speeds and all the other benefits that are gained by changing your DNS provider.