Netmask: netmask allowed by OPENVPN server 
Bridge (TAP): 
 
DHCP-Proxy mode: enable or disable DHCP-Proxy mode 
Pool start IP: pool start IP of the client allowed by OPENVPN server 
Pool end IP: pool end IP of the client allowed by OPENVPN server 
Gateway: the gateway of the client allowed by OPENVPN server 
Netmask: netmask of the client allowed by OPENVPN server 
Block DHCP across the tunnel: filter (drop) DHCP packets in the tunnel 
Now back to common settings. 
 
Port: listen port of OPENVPN server 
Tunnel Protocol: UCP or TCP of OPENVPN tunnel protocol 
Note: for maximum security and speed, choose UDP. For a reduction in 
security, TCP provides better reliability for low traffic links. 
Encryption Cipher: Blowfish CBC,AES-128 CBC,AES-192 CBC,AES-256 
CBC,AES-512 CBC