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How best to Configure iphone for failover IP scenario

Posted on 2012-09-06
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Last Modified: 2012-09-11
We have our main external IP range lets call it 66.66.66.66 for our T1 line, and firewall, and exchange server etc. The firewall has been configured for failover, so that it the T1 goes down, the DSL will kick in - it's IP's are 44.44.44.44
On the external MX records, I can send the email to the 44.44.44.44 IP's if the 66.66.66.66 is down. The iphone has an A record called iphone.myco.com which points to the IP of the mail server - say 66.66.66.01and it works fine. When the failover happens, the iphone will not get email because it is not pointing to the 44.44.44.01 (the DSL's IP for the exchange server)
Can I set up the MX records or the iphone itself so that the failover will allow the iphone to continue to get email automatically when the T1 is down?
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Question by:doreendub
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Expert Comment

by:redbmaster
ID: 38372523
You should be pointing the iPhone to the DNS MX record. But if you want to maintain a totally separate DNS record then you'll want to add the 44.44.44.01 ip address to iphone.myco.com.

Note that this isn't a true failover as DNS will round robin the IPs.
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Author Comment

by:doreendub
ID: 38372564
Hi redbmaster - I don't point the iphone to the email MX record because that points to  the spam filter we have. When I point the iphone to the spam filter it does not get email - only when I point it to the exchange server.
Also I have an A record for the iphone.myco.com not an MX record so can't add multiple IP's (or can I?)
I could try changing the iphone A record to an MX record and see if they still get email?
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by:redbmaster
ID: 38372667
You should be able to set multiple A records.

The more I think about it the less I believe this will really work for you. With this setup if either connection goes down the client device will need to refresh its DNS records until it pulls the other/working connection.
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Author Comment

by:doreendub
ID: 38372689
Hi redbmaster - what do you suggest then? I am thinking of changing the iphone A records to 2 MX records, the 1st will point to the 66.66.66.01 IP and the 2nd one will point to the 44.44.44.01 IP. Do you see any issue with that?  thanks..
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redbmaster earned 900 total points
ID: 38372742
The issue is DNS is not meant for true high availability. Some people will swear by it, but others will call it half a$$ed. I'm kind of in the middle. The thing to look out for is the TTL setting. Some people set it as low as 30 seconds and others go with 5-10 minutes. The TTL will basically tell the devices that they need to go look for a new DNS record.

The issue with DNS RR (round robin) is that it'll point devices to each external IP. So, if two devices look up the DNS record of your server one will get the 66 ip and the other will get the 44 ip, and it will continue to alternate between the two IPs. If one goes down then it technically shouldn't give it out anymore, but the clients that already have that IP will continue to fail until their TTL for that record expires.

That being said it should work, but its not going to provide an instant failover. Its a cheap way to get a failover like setup. I'd say try it out and see if its a viable solution for your company.
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Assisted Solution

by:doreendub
doreendub earned 0 total points
ID: 38373723
Thanks redbmaster for all your help. I have been reading online also and I found thsi very useful article : http://community.spiceworks.com/topic/188988-dns-settings-in-failover-situation
I think after your comments and reading the article, that it would be best if I do not chanage the iphone from A to MX. If the main line goes down I will either change the A record for the iphone or change the IP on the iphone it self. It's only 4 iphones in the company so although that is very manual, it means I will know exactly what is going where.
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Expert Comment

by:redbmaster
ID: 38376461
Ah yes, I almost forgot about this. They are talking about using dynamic DNS to provide failover. I used no-ip.com back in the day when I was hosting a few servers out of my house. I had cable highspeed internet at my house and did not purchase a static ip, so basically these work by installing a small app on a pc or server, in your case, which checks in with their server and updates your DNS record with that machine's outside IP address. This allowed anyone to connect to my servers via that domain name even if my public IP address changed at home.

I would look at your current DNS provider to see if they offer that service. If not it looks like the average cost for this service is $20-$30 a year. This price point is easily affordable by most companies. Take a look at http://www.no-ip.com/business/ for more info, and I hear good things about dyn.com, http://dyn.com/dns/dyn-standard-dns/.
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Author Closing Comment

by:doreendub
ID: 38386051
Because an article I found online also helped. I posted the article in the comment fro others to access also.
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