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DNS settings at the registrar for proper failover

Posted on 2007-07-25
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I have setup my DNS entries at the registrar the following way.  What I would like to achieve is to have a proper failover not just for the web, e-mail delivery & receipts (SMTP), but also for the pop3 clients.  Could you please help me which one setting is preffered or any other suggestions:

A (Host)  
Host      Points To                            TTL
@      69.180.6.6                           1 Hour
@      24.126.181.62      1 Hour
mail      69.180.6.6                           1 Hour
mail2      24.126.181.62      1 Hour

CNAMES (Aliases)  
Host            Points To                            TTL
ftp            @            1 Hour
webmail            @             1 Hour
www            @            1 Hour
www.webmail      @            1 Hour    

MX (Mail Exchange)  
Priority      Host      Goes To            TTL
0      @      mail.sssconsulting.net      1 Hour    
10      @      mail2.sssconsulting.net      1 Hour

==========================================================
OR
==========================================================

A (Host)  
Host      Points To                           TTL
@      69.180.6.6                           1 Hour
@      24.126.181.62      1 Hour
mail      69.180.6.6                           1 Hour
mail      24.126.181.62      1 Hour

CNAMES (Aliases)  
Host            Points To                           TTL
ftp            @            1 Hour
webmail            @             1 Hour
www            @            1 Hour
www.webmail      @            1 Hour    

MX (Mail Exchange)  
Priority      Host      Goes To            TTL
0      @      mail.sssconsulting.net      1 Hour    

Any help will be greatly appreciated.
Thank you,
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Question by:Salman121
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by:simprix
ID: 19585247
You could use DNS round robin like this. http://content.websitegear.com/article/load_balance_dns.htm. This is not true fail over. You would need a load balancer or a DNS service like DynDNS.
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Ted Bouskill earned 200 total points
ID: 19586947
DNS round robin isn't proper fail over.  All DNS round robin is is one DNS entry with two or more IP addresses.  As each request comes in to the DNS server it rotates the IP address it returns.

If you had two servers using DNS round robin, if one server dies, then every second DNS request will go to the dead server.

Use network load balancing the DNS entries for MX et cetera are set for one virtual IP on the load balancing array.  The array is aware of when a server dies and then redirects all traffic to the available servers.

NLB in Windows is free and simple to configure and there are many hardware products that do the same thing.  If you are non-windows I am sure there is similiar offerings for Linux.
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Author Comment

by:Salman121
ID: 19588215
I tested with one MX record and two IP addresses in A record as below:

MX (Mail Exchange)  
Priority      Host      Goes To            TTL
0      @      mail.sssconsulting.net      1 Hour

mail      69.180.6.6            1 Hour
mail      24.126.181.62      1 Hour

when i pinged the "mail.sssconsulting.net", it showed the first IP address, "69.180.6.6".  I brough that server down and then pinged it again.  This time it responded witht he second IP address, "24.126.181.62".  I tested with sending mail messages as well and it seems to work OK.  I just wasn't sure if this is the proper way to to setup the failover for mail server.  Any comments?

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LVL 51

Expert Comment

by:Ted Bouskill
ID: 19588503
No that isn't proper fail-over.  It is DNS round robin.  Use two different client systems and execute a ipconfig /flushdns between pings while the first server is down.  Every second request will get the first server which will fail.

Round robin DNS is NOT fault tolerant.  If a server goes down, clients will get errors.
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by:northcide
ID: 19610755
www.barracuda.com - inexpensive load balancers.
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Expert Comment

by:Ted Bouskill
ID: 19614519
Once again network load balancing in Windows is free and very easy to manage.
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by:Computer101
ID: 20286814
Forced accept.

Computer101
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