A very common use of a VPN is to route all the traffic over a secure tunnel. This allows one to safely access a network, or even the Internet itself, from within a hostile environment (for example, a poorly protected Internet cafe).
Redirecting the default gateway is achieved by adding the line
push “redirect-gateway [def1 local bypass-dhcp bypass-dns]” to the server configuration file.
The parameters to
redirect-gateway listed previously are optional, but they can play a very important role:
No parameters added: In this case, OpenVPN will replace the existing default gateway (0.0.0.0/0) with the address of the OpenVPN server itself. An extra route to the OpenVPN server itself is also added so that the OpenVPN traffic itself is sent directly to the server, instead of via the tunnel. The disadvantage is that if the OpenVPN connection is stopped or breaks down, the original default gateway is lost. This usually causes a full loss of network connectivity.