Case Study : Windows 2012 R2 – ping internally returns wrong IP on multihomed server

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As system engineer I’m providing a 3rd level support in IT areas I work on. So one day a strange case came to me.  An issue was reported that on multi-homed Windows 2012 R2 server – this case was : 2 network interfaces on Windows 2012 R2 (I can imagine it can happen on 2+ network interfaces Windows 2008 or newer). So on mutlihomed Windows Server 2012 R2, when try to ping internally FQDN wrong IP is returned.So for investigation we have :

An input :

Windows 2012 R2 server with 2 network interfaces

  • 1st network interface configured with all settings : IP, mask, default gateway and 2 DNS servers, all other settings default, registered in DNS with name server.domain.local
  • 2nd network interface configured with all settings : IP, mask, no default gateway and 2 no DNS servers, all other settings default, registered in DNS with name server.backup.local

An issue

  • resolving a fully qualified domain name : server.domain.local from any remote server with nslookup – 1st interface IP address is returned
  • pinging  fully qualified domain name :server.domain.local from any remote server – ping goes via 1st interface IP address

So far, all is fine

  • resolving a fully qualified domain name internally from server (so from server.domain.local) with nslookup server.domain.local – 1st interface IP address is returned
  • pinging  fully qualified domain name :server.domain.local internally ( so from server.domain.local) – IP address of server.backup.local is returned

So there is an issue. When I disabled server.backup.local interface then pinging server.domain.local internally returns 1st interface IP, however after enabling inteface back, issue is back. I tried reset an TCP/IP with netsh command :

it didn’t help. So after some digging, I discovered that both configured interfaces have same metric, interface metric was default, so it is “Automatic metric”.  Metric value for both interfaces was : 5

So I simply changed metric of 2nd IP interface registered with server.backup.local using simple powershell command

And issue is solved. That’s story for today.

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