Optimal DNS setup "adding extra static DNS"

[TheGorx]

I had a strange thing happen yesterday
I my ISP DNS didn't appear to be working
I couldn't get online until I tried using an IP address

so I added a static DNS to my router and I was back surfing again.
but when I added the static DNS to my third DNS and saved it
it was listed as my primary.

Also about six month ago when I moved my website
it took a while before I could access it
my server said it takes awhile before all the DNS servers get updated.

so know I'm wondering what is the best way to add extra static DNS addresses for back up.
In case of problems or even to get the best access to the web.

[Tuttle]

You only need one working DNS server configured to get things working. That's why ISPs normally provide two.

If you are going to add extra DNS servers to your config, you should check that the admin of that DNS server is OK with you using it. Otherwise you may connect one day and find it feeding you incomplete/incorrect data, or ignoring you completely.


The issue when you moved your server is something else entirely. For any domain, there are only a handful of servers (at least two, typically no more than six or seven) which are called "authoritative" for the domain. Those are the ones which have config files telling them what names resolve to what IP addresses.

All the other DNS servers on the Internet, like your ISP's, have to go back and ask those authoritative servers if you ask about that domain. To save bandwidth and server load, rather than asking for each individual request, DNS servers cache responses and keep serving old data - www.virtualdr.com resolves to 63.236.73.204 now, and chances are it's going to resolve to the same thing 10 minutes from now. Checking with the authoritative servers every time I look at a new page would be pointless.

That caching is controlled by a TTL (time to live) value, which tells servers how long they're allowed to cache the answer for before they need to ask for fresh info. For dynamic DNS services that's usually a few minutes, for normal web sites it's closer to a day or two.

When you update DNS for some reason, like moving your web site, you need to allow for the fact that other DNS servers on the Internet may have the old cached data, and may not ask for fresh data for that TTL. On the other hand, they may not have any data cached, in which case the first query will return correct data straight up.

The usual way to get around that uncertainty, btw, is to drop the TTL to a few minutes a few days before a change, then make the change and put the TTL back up afterwards.

[TheGorx]

hey, thanks for the info

probably by the time I learn about all this stuff someone will change it.
or maybe they'll get smarter search engines that can match domain names and ip addresses.

having googles ip address only gets you so far without the DNS working.