Issue #12604 has been updated by Tomoyuki Chikanaga.

Backport changed from 2.1: WONTFIX, 2.2: REQUIRED, 2.3: REQUIRED to 2.1: WONTFIX, 2.2: REQUIRED, 2.3: DONE

ruby_2_3 r57571 merged revision(s) 55781,55783.

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Bug #12604: Win32::Resolv.get_resolv_info returns unavailable DNS servers
https://bugs.ruby-lang.org/issues/12604#change-62904

* Author: Lars Christensen
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.2.4p230 (2015-12-16 revision 53155) [i386-mingw32]
* Backport: 2.1: WONTFIX, 2.2: REQUIRED, 2.3: DONE
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`Win32::Resolv.get_resolv_info` returns a list of IP address that include DNS server for network devices that are not connected, causing long timeouts when using `Resolv::DNS` (or Rubygems which uses `Resolv::DNS`)

`Win32::Resolv` scans the registry for DNS server addresses. Unfortunatly, if some of your network devices are not currently connected, the old DNS information is still stored in registry. So `get_resolv_info` still returns it. This can cause very long timeouts when using `Resolv::DNS` (e.g. rubygems). For example, a simple 'gem install' on my machine would take over a minute, because of several timeouts waiting for DNS.

Example:

```ruby
irb(main):024:0> Win32::Resolv.get_resolv_info
=> [["mynet", "mycompany.local", "local"], ["192.168.1.1", "172.27.0.1", "8.8.8.8", "8.8.4.4", "192.168.101.10", "192.168.101.11"]]
```

* 192.168.1.1 is the DNS server from my home Wifi (not currently connected)
* 172.27.0.1 is the DNS server from a router I had connected via an USB Ethernet Device a week ago
* 8.8.8.8 is from the same as above (but incidentally works, since it is available)
* 192.168.101.10+11 are the actual current DNS server

I think a solution could be to rely on `GetAdapterAddresses()` in the Win32 API instead to get the IP address of DNS server.

As a workaround for users affected by this is to remove unconnected Interfaces from `HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces` in the registry.




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