Disable local IPv6 while connected to an IPv4-only VPN #142

When connecting to an IPv4-only VPN while connected to a dual stack local 
network, new connections to hosts reachable over IPv6 are still established 
using the local address (verified by accessing various "what is my IPv6"-sites 
- they all report my local address).

Is there a way to disable IPv6 connectivity for the duration of the VPN 
connection from within the VPN API? Cisco AnyConnect seems to be able to do it, 
since on the same network, when connecting to the Cisco VPN, IPv6 hosts become 
unreachable.

There should be at least an option for that, since unreachable IPv6 hosts are 
preferable to traffic being routed over the local address from a security 
viewpoint.

Or can this possibly fixed by a server-side setting, maybe by pushing an 
invalid IPv6 route?

If it helps, I can post the output of 'ip route' when connected to AnyConnect 
and OpenVPN later today - I don't have IPv6 connectivity right now.