When changing DNS records, it may take up to 24 hours till all the internet servers receive new information. Maximum time is set by TTL parameter.
What is TTL?
TTL abbreviates “Time To Live”. It is set in second and determines for how long is the DNS setting stored in cache memory of DNS servers of the internet provider. Often used value is 86400 sec which is 24 hours. After the TTL period expires, DNS settings has to be stored anew.
Why can take change in DNS records up to 24 hours?
Computers access the destination server with the content trough different ways. They ask different DNS servers for IP address of destination server. Servers that are “along the way” store the DNS records to cache memory for easier access. This time of storage is determined by TTL parameter. That is why DNS server may have stored old records which is provided to any computer asking for the destination address. Record is stored until the TTL expires. Then the DNS server updates its stored records.
How to find out that the change has taken effect?
If you know the IP address of the destination server, you can run a ping command in the command line (e.g. “ping 37.9.169.171”). If you do not know the IP address, you can use command tracert (e.g. “tracert active24.cz”). This command will show you the nodes your computer is accessing on its way to the destination server.
Change has not taken effect even after 24 hours, how so?
It is possible that in the unique cases the change can take more than 24 hours. For example any of the DNS servers “along the way” may have stored records with higher TTL than 86400 seconds. Another reason is that original DNS is stored in the local cache memory of your computer. This memory can be emptied by command Flushdns.
In Windows follow this guide:
- Select Start and run “cmd”. In newer version of Windows you can search “cmd” and press “Enter”. Older version require to first select “Run” and then enter “cmd”.
- To the command line window enter command “ipconfig /flushdns” and press “Enter”. A confirmation message will let you know that the cache has been emptied.