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I just used "" to test my DNS setting.

What is this below problem? How to solve it?

Different autonomous systems    WARNING: Single point of failure


Different subnets   WARNING: Not all of your nameservers are in different subnets
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migrated from Mar 28 '11 at 7:39

This question came from our site for professional and enthusiast programmers.

up vote 1 down vote accepted

The subnet error just means you're putting all your eggs in one basket!

There's an RFC, if my memory serves, that asks for two different physical locations (or at least subnets) for the Name Servers under a Domain. It's not always needed because one location might have multi-homed bandwidth or other resilience available but generally it's not that good an idea keeping all your NSs in one place.

Another school of thought is that if you're just serving some services alongside your NSs (eg your Name Server is on the same machine as your Web Server) and that service is no longer available, due to an outage of some sort, then what's the point in having backup DNS ? It won't make much difference to visitors.

Mail Servers tend to also hold undelivered mail for so long these days that even backup MX are hardly needed in practice, although I'm an advocate of secondary MX.

As for the first error ... no idea :-)

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No idea what that first error means without more context.

The second error means, if your subnet hosting your DNS servers dies, you'll be stuck without any hosts that can answer DNS queries from clients. So make sure you've got DNS servers hosted on several different subnets.

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My best guess for the first is that has concluded that your nameservers are in the same location by finding the AS numbers for each nameserver. It is a similar problem to having them on the same subnet.

For reference, the result for my domain for that category is, "OK. It seems you are safe from a single point of failure. You must be careful about this and try to have nameservers on different locations as it can prevent a lot of problems if one nameserver goes down."

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