openvpn: after changing to server mode, client does not create TUN device

Solution 1:

In the client config use:

client

A helper directive designed to simplify the configuration of OpenVPN's client mode. This directive is equivalent to:

 pull
 tls-client

In the server config:

server 10.8.117.0 255.255.255.0

expands to

 mode server
 tls-server
 ifconfig 10.8.117.1 10.8.0.2 
 ifconfig-pool 10.8.117.4 10.8.117.251
 route 10.8.117.0 255.255.255.0

A helper directive designed to simplify the configuration of OpenVPN's server mode. This directive will set up an OpenVPN server which will allocate addresses to clients out of the given network/netmask. The server itself will take the ".1" address of the given network for use as the server-side endpoint of the local TUN/TAP interface.

For example, --server 10.8.0.0 255.255.255.0 expands as follows:

 mode server
 tls-server

 if dev tun:
   ifconfig 10.8.0.1 10.8.0.2 
   ifconfig-pool 10.8.0.4 10.8.0.251
   route 10.8.0.0 255.255.255.0
   if client-to-client:
     push "route 10.8.0.0 255.255.255.0"
   else
     push "route 10.8.0.1"

 if dev tap:
   ifconfig 10.8.0.1 255.255.255.0
   ifconfig-pool 10.8.0.2 10.8.0.254 255.255.255.0
   push "route-gateway 10.8.0.1"

So the explicit tls-server is not required.