Can you give me a clear comparison of both the topologies?
topology net30 is the default mode; each client is assigned a miniature /30 network containing 4 IP addresses
10.8.0.64 network address (not used, but required)
10.8.0.65 virtual endpoint address (needed, but not pingable)
10.8.0.66 client VPN IP address
10.8.0.67 net30 broadcast address (not used, but required)
The IP address of the client is always X.Y.Z.(4*n+2), netmask 255.255.255.252, where "n" is 1,2,3,4 etc
topology subnet assigns a single IP address to each client, with netmask 255.255.255.0; it closely resembles 'dev tap' mode but there are fundamental differences.