Internet Propagation
What information do the Name Servers have?
The information inside of the name servers is referred to as the “Zone File”. It contains a number of different pieces of information which are classified into different sections called records.
1) NS Record – This record is just an internal record that points back to the Name Server it resides inside of. (example: inside of the name server “ns1.site.com” is an NS Record that points back to “ns1.site.com”.
2) MX Records – This controls where an incoming email should be sent to. MX stands for the term “Mail Exchange”.
3) A Records – This is the entry that controls what IP address to point to. There are usually a few different Address Records being used at one time:
example.com A 209.25.195.50
www.example.com A 209.25.195.50
ftp.example.com A 209.25.195.50
mail.example.com A 209.25.195.36
Each of these A Records can go to a different IP address if you wish. You may have the A Record of (mail.example.com) point to the IP address of your email server and then you can set your MX Record to be: (mail.example.com). This lets email come in to the correct server for your domain.
4) CNAME Records – This stands for Canonical Name which is just too hard to say so people just call it CNAME. This is an entry that just points to another name, not an IP address. As an example you may point your domain name (example.com) to the IP address but then setup a CNAME for (www.example.com) to point to the name (example.com):
www.example.com CNAME example.com
When someone looks for the name of (www.example.com), the CNAME say to go to (example.com). Since the entry for (example.com) is an A Record that points to the IP Address, the persons web browser goes to the correct website in the end.
Internet Propagation
What exactly is “propagation”? Why is it important? Basically the term propagation is used to talk about the amount of time it takes for the entire Internet to learn of a change with the name servers. There are a few types of changes where this can become important.
The most common type of change is to change the Name Servers your domain name is using. This is usually done when you already have registered a domain name with a company such as www.GoDaddy.com but you decide to get web hosting at another company such as 1&1 Web Hosting. The advantage to this is their name servers usually are already pointing everything correctly for your account with them. You don’t need to make any further changes to get it to work from that point on.
Another type of change you make is to keep your current Name Servers and just change one of the records inside them to point to a new location. This could be a new IP address for an “A record” or a new mail server for an “MX record”.
The time period for this change to take effect on the Internet can range from just a few minutes up till 72 hours. This depends on the speed of update getting put into the Name Servers as well as how long the rest of the Internet uses the old information before looking up new records.
Once a lookup for a domain names website or email server is done that information is kept and reused for a period of time before a new lookup is done. For example; someone using their cable modem in Australia sends you an email. The company that provides the internet connection in Australia for that user will look up your domain name and find the MX record so they can send that email to your domain.
Once that MX record lookup happens the company in Australia will keep using that same information for a period of time, maybe 12 – 24 hours, and not look it up each time someone sends an email. If you changed your Name Servers right after they did a lookup on your domain they will not learn of the new information till they do a new lookup in 12 – 24 hours. They will keep sending information to the first MX record they found.
Why is this important to you and your site? If you plan on making changes to your Name Servers on your domain keep in mind that the entire Internet will not learn about the change at the same time and it can take 24 – 72 hours for this “propagation” period to complete.
I hope I didn’t get into too much detail, I tend to get carried away at times. It’s not really important to understand everything I covered in the article but the main important facts are the Name Servers are what control all the pointing of traffic for your website. If you wish to make a change to point to a new location for website or email, expect a 24 - 72 hour delay to get completed.
Thanks,
Jim
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