Tente alterar
push redirect-gateway def1
route 192.168.0.25 255.255.255.0 net_gateway
route 10.8.0.0 255.255.255.0
para
redirect-gateway
e
push dhcp-option DNS 10.8.0.1
push dhcp-option DNS 192.168.0.25
push dhcp-option DNS 8.8.8.8
push dhcp-option DNS 8.8.4.4
para
dhcp-option DNS <YOUR_ROUTER_LOCAL_IP_ADDRESS>