[strongSwan] How to route all client traffic through the server?

[Neddie Seak]

I am working my way through a simple example of a road-warrior with certificate authentication, based on https://www.strongswan.org/testing/testresults/ikev2/rw-cert/

By adding a virtual address pool to the server swanctl.conf, similar to the Roadwarrior scenario at https://wiki.strongswan.org/projects/strongswan/wiki/UsableExamples, 

primary-pool-ipv4 {
    addrs = 172.16.252.0/24
    dns = 8.8.8.8
}

and by adding a line to the client swanctl.conf:

vips = 0.0.0.0

the server assigns a virtual IP address to the client, 172.16.252.1/32. This can be confirmed with the command:

ip a

However, nothing is added to the client's route table. The output from the command:

ip r

does not change. And the client continues to use its regular Internet gateway instead of the tunnel to the server.

How do I get the client to send ALL its traffic through the tunnel to the server?