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Fail Over DNS

Posted on 2011-02-16
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Last Modified: 2012-05-11
What is the option if a server fails at one location and you bring it up at another location, is there a way to have a fail over dns record for e-mail? I am guessing that would just simply be a higher number in the MX record, but is there a service or way of setting it up if one MX was not responding it would fail over to the other server?
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Question by:patrickschuler
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Expert Comment

by:Busbar
ID: 34905109
you can setup another MX as you said with a higher priority on your DNS server, mail servers will try the first if not it will pickup the second one, this is done automatically.
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Expert Comment

by:andreizz
ID: 34905118
I think it does that automatically, you just have to add on the primary server the secondary mail server dns record, like you said with higher MX number.
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Expert Comment

by:Ernie Beek
ID: 34905442
Just have a second MX record with a higher preference, just like this:

google.com      MX preference = 100, mail exchanger = google.com.s9a1.psmtp.com
google.com      MX preference = 200, mail exchanger = google.com.s9a2.psmtp.com
google.com      MX preference = 300, mail exchanger = google.com.s9b1.psmtp.com
google.com      MX preference = 400, mail exchanger = google.com.s9b2.psmtp.com


First, the lowest preference will be tried (100). If that doesn't respond the second lowest will be tried. If that doesn't respond, etc.
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thehagman earned 500 total points
ID: 34906437
For a server move (chacng of IP from 11.22.33.44 to 55.66.77.88) I suggest

yourdomain.com  MX   10  mail.yourdomain.com
yourdomain.com  MX   20  new-mail.yourdomain.com
yourdomain.com  MX   100  fallback-mail.yourdomain.com
mail.yourdomain.com  A  11.22.33.44
new-mail.yourdomain.com  A  55.66.77.88
fallback-mail.yourdomain.com  A =??.??.??.??   (should be online during the whole move process)

Once the move is complete, you may sort things out, e.g. remove all references to old IP and rename new-mail t mail.
In principle you *could* leave old data in DNS, but: Mail transfer would slow down as everybody would first try the obsolete server; and if you hand back the old IP address range, someone else may obtain the IP address and might catch your mail

ANother hint: You may need to be careful if you use the same server for outbound mail as then hostname and EHLO greeting should match (and should match reverse DNS)

You may even try

yourdomain.com  MX   10  mail.yourdomain.com
yourdomain.com  MX   100  fallback-mail.yourdomain.com
mail.yourdomain.com  A  11.22.33.44
mail.yourdomain.com  A  55.66.77.88
fallback-mail.yourdomain.com  A =??.??.??.??   (should be online during the whole move process)


Actually, you may be able to do this without fallback mail server as sending mail servers will themselves buffer mails for a while (typically days) and retry. A fallback mail server does however reduce the possibility of annoyance at the sender side.
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Expert Comment

by:Krzysztof Pytko
ID: 34913762
If it's domain environment and you have DCs with DNS installed and your DNS zone is AD integrated then that's no problem. Your DNS server is up and running if one of them would fail, each of your DNS server contain read/write DNS zone(s). Just remember that you have to specify in NIC's properties of each statically configured machine 2 or more DNS servers IP for failover. Also in DHCP server modify option no 006 to provide 2 DNS server to your DHCP clients. That's all

Regards,
Krzysztof
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Expert Comment

by:PacketExchanger
ID: 34918765
You can use a GEOdns service, and route your mx through a load balance, failover solution, so in case your mail server looses connectivity or services are failing, then the load balancer should have an active failover rule which will change request from going to the bad location, you can also use this to distribute the load evenly for high request.


check www.3crowd.com        they can provide this service for you


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