This seems to be a general problem, but I couldn't manage to solve it.
I have a very simple configuration which follows. The server is Windows Server 2003 and client is Windows 7 Ultimate. On both, OpenVPN runs as service. I patched the "IPEnableRouter" value to 1 on OpenVPN server machine.
I CAN ping and connect ports on VPNSRV, but I CAN'T connect to any port on FTPSRV from CLIENT. VPNSRV don't have any problems connecting to FTPSRV.
Verbose logging shows that OpenVPN takes packets from CLIENT then writes, but no reply returns when pinging FTPSRV. Things are fine with pinging VPNSRV
CLIENT: LAN(192.168.2.x), OPENVPN(10.10.43.x) VPNSRV: LAN(10.10.0.3), OPENVPN(10.10.43.1) FTPSRV: LAN(10.10.0.6)
client proto tcp dev tun dev-node lanvpn remote vpnserver 10000 resolv-retry infinite nobind mute-replay-warnings ca ca.crt ns-cert-type server cipher BF-CBC comp-lzo verb 3 cert client.crt key client.key
port 10000 proto tcp dev tun dev-node lanvpn ca ca.crt cert server.crt key server.key crl-verify crl.pem dh dh1024.pem cipher BF-CBC comp-lzo ifconfig-pool-persist ipp.txt server 10.10.43.0 255.255.255.0 push "route 10.10.0.0 255.255.255.0" keepalive 30 120 status openvpn-status.log verb 3