Windows only supports two DNS servers for VPN sessions
03/26/2020 16 6285
When configuring an SMA 1000 series appliance three DNS servers can be configured.
However on a Microsoft Windows PC logged into an SMA only the first two DNS servers are shown in 'ipconfig /all'.
If the first two DNS servers fail no DNS lookups are possible over the VPN because the third is not functional on Windows PCs.
Other operating systems, e.g. Linux, are provided all three DNS servers.
Windows only supports two DNS servers on a VPN connection. The PC is not aware of and not able to access the third DNS server behind the SMA.
Plan for this limitation and do not depend on the third DNS server being functional for Windows tunnel clients.