Yes, it even has come to this: mere mortals can use it at home. The audacity!
Unfortunately not all vendors (if any?) have feature parity, in our case a specific VPN product doesn't support IPv6.
The client will only receive an IPv4 address from the VPN server.
When the user at home starts it's VPN and asks for an internal resource (which also has an IPv6 address), it will try to connect to this resource using the IPv6 from his provider (he didn't receive one from the VPN server) which doesn't work, because this specific resource is firewalled for outside addresses.
Luckily the user has to use our DNS server to look up records (forced to do so by the vpn client)
Luckily we're using PowerDNS recursor which has support for LUA scripting which can modify DNS responses.
The script below gives normal answers to every host not coming from 10.100.0.0/15 or 10.0.0.1/32. Otherwise if the answer contains an AAAA, drop it, and return the rest.
More information about LUA scripting for PowerDNS can be found here: http://doc.powerdns.com/html/recursor-scripting.html