Connection to VPN adds unreachable IPv6 address

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Joined: Wed Sep 26, 2018 12:21 pm

Post by bitbucketfail » Fri Sep 28, 2018 9:13 am
On Windows 10 some applications fail to connect to public website when VPN is connected.

After some digging I found out that nslookup returns 3 IPv4 and 3 IPv6 addresses for the host. These addresses are the same before and after connection to VPN.

For some applications situation is a bit different. When VPN is NOT connected then getaddrinfo() windows function returns 3 IPv4 addresses. These addresses work fine and connections can be made.

After connection to VPN the same call to getaddrinfo() returns 3 IPv6 and 3 IPv4 addresses. In this case IPv6 addresses are unreachable but they are at the start of the list so any attempt to connect now fails.

I noticed that Outlook had the same connection problem if it was started after VPN connection was made.

So why connection to VPN adds 3 IPv6 addresses for the host? How can I get rid of them?


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Post by Eric » Fri Sep 28, 2018 12:04 pm
Hi bitbucketfail,

The DNS server your VPN is most likely different to the one you use regularly, it's not uncommon for ISP DNS servers to not resolve IPv6 if they do not offer IPv6 connectivity. If your VPN server does not offer IPv6 connectivity, then those IPv6 addresses are ignored by Windows, they are not being used and would not be the problem here.

Applications can force getaddrinfo to return IPv4 addresses only - ... etaddrinfo

I recommend you contact your VPN Provider for more assistance with this - ... providers/

Eric Thorpe
Viscosity Developer

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