Internal Name Resolution and Failover

[MoonRise]

After searching the forms and Google for some hours I have decided to post, apologies if this has already been answered.

I am setting up a SIP phone to register to one of two internal servers (they are internal now, in the future they will have public IP addresses), the primary server and a fail-over server. What I want to happen (and I can't believe I am the first one) is for the phone to register to server A until it goes offline then register to server B, once server A returns then register back to it.

I tried using two entries in Service –> DNS Forward --> Host Overrides that looked like this:
Host=myhost
Domain=testregister.com
IP address=192.168.2.105

Host=myhost
Domain=testregister.com
IP address=192.168.2.106

Once complete I entered testregister.com as the register server address into the phone along with all other needed info (username, password, etc...) and the phone failed to register. I also tried pinging testregister.com from a local windows machine and it could not resolve an address.

Next I found info on wildcard entries in the advanced field of Service --> DNS Forward. I entered "address=/testregister.com/192.168.2.105" and this worked. I then tried to enter a second line below the first "address=/testregister.com/192.168.2.106" and disconnected the SIP server at 192.168.2.105 and the phone would not register.
Lastly I put the entry of "address=/testregister.com/192.168.2.105/192.168.2.106" in the advanced box and thought I had it. The phone registered to .105 and then when .105 was disconnected it registered to .106. My only problem at this point is that when .105 came back online it stayed registered to .106 (not something I want happening in the real world).

As I said at the top I can't be the first person to want to do something like this and I might be completely the wrong area. I would also guess that my terminology of "fail-over" might be wrong in this case. Any help you can provide would be welcome.

[cmb]

Those host overrides as defined would resolve only "myhost.testregister.com", not any other hostname. Leave host blank if you want just "testregister.com" to resolve to that override.

That said, DNS is the wrong way to go about that. What you're doing there is creating a round robin DNS record, which will have at best unpredictable results when trying to do what you're wanting. Phones would connect to one or the other, and may eventually switch to the other address depending on how their DNS resolver functions, but it won't work well.

What you probably want there instead is to configure the phone with host1.example.com as the primary and host2.example.com as the secondary. Most phones have some concept of a backup registration server.

[MoonRise]

I agree that most phones have a fail-over registration but some don't and those who do only have two entries (we may want to fail-over to one of three locations, two in the cloud one onsite). Does anyone know how to do this in the router itself?