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faillover 3rd DNS Server

Posted on 2002-05-22
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Hello,

At the moment we have a primary and a secundairy DNS. In case our internetconnection should cause troubles, we want to redirect our customers to a another webserver (different location) which for example displays a temp webpage.

Could this be done by using a 3rd DNS server located in a different area using a different zone-file?

I guess not because the secundairy dns'ses need to be exact the same as the primary. But is there some other way to do this?

Regards,

Rick
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Question by:rmulder
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by:Mishou
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Mulder,

You are concerned that if your Internet connection goes down your web site cannot be accessed.
When you registered your domain you specified 2 DNS servers.
I can think of a way to have your problem solved with the folowing configuration:
-install one DNS server at your location.
-install the other one somewhere else (or register with companies that provide DNS service).

The DNS at your location is the primary DNS specified in your zone and contain all the information the way that you want it.
The other DNS will contain same information except that your for www.company.com record will point to another webpage that display the temporary page.

This way when a client access your page, he will first contact the DNS at your location to translate www.company.com into an ip address.
If he cannot contact the first DNS specified on your zone, will try the next one.

There are some issues though with the fact that once one DNS is contacted that information is cached at the client side (for fast name resolution).
Maybe you will have to place a warning/description on the temp page asking the client to try to access the real page.

Hope this answer/help you.
Mishou
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by:rmulder
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It's not correct to think the 1st DNS is always used first. The 1st and 2nd DNS are being randomly chosen.

So i guess that's not going to work :-(


Gr,

Rick
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by:Mishou
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I'm sure that when you register the zone (www.company.com) with the .com root server you actualy have to provide a primary and a secondary DNS server for your zone.
The random access of these 2 servers is configured using round robin or other form of balancing . But still there is a precedency created . primary and then secondary to be tried.

Or copy the site on the second webserver (in case the DNS access is random) and change the page on this server if the other link goes down (or have a monitoring tool to do this).

Mishou
 
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by:Comply
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You don't need a third DNS server. Just redirect to your seconary DNS server. Most web hosting companys have a utility just for this. I would make a image copy of my first DNS server, Then the they would never know they got redirected or your first server was down. Also if for any reason you lose a drive you can restore from the image back-up.
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by:Comply
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You don't need a third DNS server. Just redirect to your seconary DNS server. Most web hosting companys have a utility just for this. I would make a image copy of my first DNS server, Then the they would never know they got redirected or your first server was down. Also if for any reason you lose a drive you can restore from the image back-up.
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meverest earned 500 total points
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mulder - you are correct - there is no way to determine which dns will service the reolver request.  if you try to do what has been suggested (ie different A records for different name servers) the reulst will be unpredictable.  keep in mind also that dns has caching component.  thus (for example) if a client af ISP 'x' looks at your web site in the morning, then their local DNS will resolve the hostname to IP address then cache that result for a time specified by the dns administrator of ISP 'x'.  therefore if your net connection fails, and (by some magic) a backup dns serves the address resolution as a different IP, those customers of ISP 'x' will still get a 'server not found' when attempting to hit your web site.

one method to acheive what you want is to use routing techniche instead of DNS.  the way this works is that you set up your backup server with exactly the same (REAL) IP address of your primary, even though it is on a physically different network.  use a dynamic routing protocol (like BGP is good for this sort of purpose) to advertise independent paths to these two locations.  if you load up the routes to your backup server, then when your primary site is online, then requests will always find their way to the primary server.  if it goes offline, then your border router will (obviously) stop advertising, so then the routes to the secondary location will kick in, and so direct requests to the backup server.

this is far more feasible technique than using something as inconsistent as DNS.

there are plenty of provisos and gotchas tho, so you'll need some fairly advanced network gear and plenty of nouse to get it working.

good luck! ;-)

cheers.

 
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by:rmulder
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tnx
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