Techno Tip #1: Strange Domain Behavior? Could Be a DNS Propagation Problem!

If you’re not familiar with the way that domains and web hosting relate to each other, read this first.

dnsAny registered domain “points” to a server (normally TWO servers–primary & secondary—for redundancy). They’re called “domain name servers” (DNS). These named servers are the physical devices where your website files and email accounts actually live. The Internet Corporation for Assigned Names and Numbers (ICANN) maintains a master database of DNS records. Each DNS record contains the domain name and the domain’s associated named servers.

When you access a website through an Internet Service Provider (ISP), the ISP locates the website’s DNS records and sends you to the servers identified in those records.  The ISP may be a cable company, phone service provider, satellite dish provider – whoever provides the Internet service for wherever you happen to be at the time.

So what’s the problem?

The problem with this whole scheme is that in order to speed up the rate at which their customers can view the Internet, each Internet Server Provider caches their DNS records. This means that they make their own copy of the master records, and read from them locally instead of looking them up on the Internet each time someone wants view a website. This actually speeds up web surfing quite a bit, by (1) speeding up the return time it takes for a web browser to request a domain lookup and get an answer, and (2) actually reducing the amount of traffic on the web therefore giving it the ability to work faster.

The downside to this caching scenario is that each company or ISP that caches DNS records only updates them every few days. There’s no standard for this, and each ISP can set this time to be anywhere from a few hours to several days. So if, for example, you change web hosts (which changes your domain name servers), the change won’t be accurately reflected in an ISP’s DNS records database until the ISP actually updates their database cache by going out to fetch updated DNS records.  The updating of the DNS cache is called “propagation”, since your website’s DNS information is being propagated across all DNS servers for all ISPs on the web. Until propagation completes, you can potentially experience different results from different ISPs. Since the cache-refresh time can be different for each ISP, it can take anywhere from 24 to 72 hours for DNS changes to be totally in effect. Until then there may be some ISPs with old DNS records, and some ISPs with updated ones.  So if, for example, you have one ISP at home, and a different ISP at work, you might get different results when you attempt to access your domain (website, emails, etc.) for a little while, until the DNS records have been updated by every ISP you’re using.  As if this wasn’t complicated enough, your accessing of a particular site on the Internet can sometimes be routed through a different set of Internet servers.  In other words, the path that’s taken by your ISP to get to the website you’re looking for isn’t always the same.  So you may access your desired website just fine now, and in a half hour (if the route changes), you may run into a non-updated DNS cache and NOT see what you expected.

Just be patient.  The whole propagation cycle should be completed within 3 days.

If you have questions about this process, please contact me.

“Tech’s not scary when knowledge tags along” SM

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