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Howdy,

We have some servers that are hosted in Azure. They power themselves on around 2:30AM every morning and power off at 6AM. In between those times they do some file syncing. The Azure servers are connected to our data center by a VPN type connection.

Anyway, I wanted to test when the machines become reachable on the network and when they drop off so I ran some overnight pings (test-connection) in Powershell. I got some strange results. The server came online every day around 2:36AM, but pings were not reliable. As you can see in the screenshot, the machine responded to pings when it first came up, but then stopped responding. Then it would start responding again, and then it would stop. The Stopped duration was usually right around 20 minutes. Then it would respond for a minute or two and then it would stop again.

Last night I tried pinging the server twice. First by name and second by IP. The Name based pings repeated the data in the screenshot. The IP based pings worked perfectly the entire time and never had a failure.

So, this seems to have something to do with DNS, but I’m not sure what. DOes DNS have a built in throttling that it would block ping requests after it gets too many in a row? Is there something built into Azure that would cause this? The Domain Controllers are local to the machine doing the pinging while the server it’s pinging is in Azure.

I’m kind of at a loss and just looking for any ideas on way to solve, or ways to get more info, so we can figure out why this is happening.

Thanks!

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When the pings by name fail - is dns returning the correct IP ?
How are the dns entries made? does the server self register - if so is it set to do so only on the 1 nic used via the vpn?

Once it works by name it should keep working (if the ip does) as the client caches the response.

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Are the IPs static or DHCP? Kind of sounds like a DNS scavenging problem.

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Forgot one of the screenshots. This one shows how both were working just fine and then the Name just stopped working. Then after a while it would start working again. Servers self register in DNS. They have two NICs but only one is supposed to register. I’ll double check that.

All IPs are Static

I’ll have to see if there’s a way to put what the IP was that it was trying to piing. I’m just using: test-connection $server -count 2 -quiet and then taking the True/False that it returns.

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OK. I think I figured out the problem. These machines all have two NICs. One of them is not supposed to be registering in DNS, but it was. Of course, that’s the IP it was trying to ping which won’t work. I unchecked the Register in DNS box and deleted the DNS entry and now it’s pinging fine. I’ll let it run overnight like usual and hopefully that’s all it takes.

I’m not sure why it would work for a bit, and then stop and start, but as long as this makes it work the way it’s supposed to, I’m good with that. :slight_smile:

Thanks.

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