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What Is DNS Propagation?

 

Any time that DNS changes are made (on any level), you need to wait for propagation to complete. Propagation usually takes from several hours to 5 days, but can take as long as 7 to 10 days. During propagation, traffic may come to either location. One person may see the new server while someone else sees the old one. Also, yourdomain.name may work while www.yourdomain.name does not. All of this is normal during propagation.

Note that this means that just because you go to the new site when you type in the domain name does not mean that propagation is complete. The best way to determine whether or not propagation is complete is to review the statistics for each site (both the old one and the new one).

Detailed explanation of propagation:

DNS stands for Domain Name System. Every time you go to a website using a domain name, you are using DNS.

  • Your request for "domain_name.com" or of any of its records goes to your local DNS server (which is usually administered by your ISP). Your local DNS server checks its cache to see if it "knows" what IP address that domain points to or if it already has any of the queried records. If it does, then it provides you this information. If it does not, then it sends a query to the Root DNS servers.
  • The Root servers are what makes the process work. When a domain is registered, it is added to the Root servers. When a domain is expired, it is removed from the Root servers. The Root servers tell your local DNS server which DNS servers ("out there") are Authoritative (are the primary and secondary DNS servers) for your domain.
  • Your local DNS server then queries the Authoritative DNS server, also called Name Server, and the Authoritative DNS server tells your local DNS server what IP address the domain is located at or what any needed records point to.
  • Your local DNS server then caches (makes a copy of) this information. This caching process is essential: not only does it speed up future queries, it also reduces the load on the Root servers. It is this caching process that leads to propagation. You may change the DNS records for your domain, but the local DNS server cache is still to be updated with the new information.

But this local DNS server does not keep that information forever. Instead, it keeps the information for a certain amount of time, at which point it deletes it. The next time that you try to visit that domain (after the information is deleted), the process starts all over again and the local server updates its cache with the new relevant information. The time the information stays cached is defined by your DNS records setup. This parameter is called TTL (Time to Live) and is specific for each DNS record.

How to check the propagation status

In order to check the propagation status at several locations worldwide, you may use such online tools as What's My DNS?.

How to calculate the propagation time for domain name records:

  1. Find the TTL for this record. TTL is the time that any remote servers in the Internet should keep your DNS records in their cache. You can check it at Network-tools web-site, for instance. Select DNS Records, enter your domain name in Search field and click Go. The records will be displayed with their TTL specified in seconds.
  2. Find the SOA section. Your main DNS Server (Authoritative Name Server) and other parameters are listed there, such as:
    • refresh: this is the time when the other Name Servers should sync with the main one to check if there were changes;
    • retry: if the DNS servers do not respond to a query for your domain in this number of seconds the Root DNS server will try again;
    • expire: if the DNS sever did not respond at all this is the time the Root DNS server keeps the last available records in its cache.
  3. When you make any changes to your DNS records, they first appear on the Authoritative DNS server, the one that is listed in SOA section. Then, in refresh time they appear on other Name Servers too.
  4. Keep in mind that propagation will be TTL+refresh because if your local server hits Name Servers other than Authoritative Name Server it might still get the non-refreshed records.
  5. If it is possible to allow for another hour of propagation then do so.


Note: You might want to change the TTL to a lesser number of seconds to make the propagation quick. Keep in mind that it is also the DNS records change and the new TTL will have to propagate as any other parameter and will take old TTL+refresh time.

 
Article ID: 797
Keywords: propagation dns domains name
Direct Path: http://hosting.intermedia.net/support/kb/viewKBArticle.asp?id=797