DNS failover

revo1059 used Ask the Experts™
We have a server on our network that is public facing. We have Comcast cable and ATT fiber running into the building and a firewall that can handle both. I'd like to set something up that if a client goes to (mysite).com and the cable modem is down (the "primary" service) it would failover to the fiber connection to the server automatically and switch back when the cable came back up, so the server is always the same server and the client is always using www.(mysite).com, just how they get in would change depending on if a service provider is down.

What are my least expensive options for that?
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actually counter to common belief the cheapest way to do that is an external service.

I'll explain.

Both addresses are basically on the same gateway (Your Firewall) so it can't actually be used to perform the balance as most firewalls don't have a DNS server. You would need to take up another line and use it to have a smart DNS server with health checks.

However, you could use Route53 by AWS, which is rather cheap these days, and has various health checks available. I'd suggest you check their website.
Most Valuable Expert 2015

If you're a small business with critical DNS and you are using an Active/Passive configuration with your two providers, Route 53 is the way to go.

If you have your own address space that is used with both providers, consider puck.nether.net (free secondary DNS).
Top Expert 2016

or use cloudflare and set up 2 entries.
A www.abc.com  <your one public ip>
A www.abc.com <your seconds public ip>
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You probably won't like my answer.

And it also sounds like you're asking about more than just DNS.

For DNS only, just use your site Registrar's DNS + likely they have redundant DNS servers, which is a basic ICANN requirement for all Registrars.

For more than just DNS, read on...

Provisioning companies provide this by default.

You lease a server, likely $100-$200 USD/month, somewhere like OVH.

They provide redundant connections, by various networks, across primary global backbones.

If part of the global net goes down (regular occurrence), packets route a different way, so your site is always accessible.

If you must go further, then you setup a multi-instance site, where multiple copies/clones of site run on various machines + round robin your DNS... meaning... mysite.com may resolve to 10 IPs... different IP every lookup.

If you really must run a local site, first + foremost, ensure all your gear (router + wifi + server) runs on a UPS, with very long battery life, else every power blackout or brownout or cycle down, will take out your network + server.

Then search for multiple isp load balancing + choose the hardware which fits your budget.
Top Expert 2014

A number of DNS providers provide simple monitoring/failover services such that when a website cannot be reached via one IP then the A record is modified to return a different IP.
Pretty sure that's what AWS Route 53 is doing.  UltraDNS has it.  I've seen it mentioned on others but I don't have a list handy.

Note that this is isn't really a function of DNS, but additional functionality that some DNS providers have tacked on (which explains why you won't see the feature if you go looking for it on a Microsoft server with the DNS server feature installed).


We do have battery backups and 2 generators to keep the entire building running so our facility itself is fairly well set against power outages. I'm just looking to backup our fast but not always 100% reliable Comcast business service with a fiber connection that we will be sharing with another business next door.

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