Используется openvpn. Сервер CentOS 5.10, клиент: windows xp.
Скорость соединения без openvpn: download speed: 18 mbps, upload speed 6 mbps.
После подключения openvpn: download speed: 1 mbps, upload speed 1 mbps.
Интернет 4g lte.

Server config:
Code:
port 1194
proto udp
dev tun1
tls-server
server 192.168.100.0 255.255.255.0
keepalive 10 120
persist-key
persist-tun
status openvpn-status.log
client-config-dir /etc/openvpn/client
push "redirect-gateway def1"
push "dhcp-option DNS 8.8.8.8"
duplicate-cn
ca /etc/openvpn/keys/ca.crt
cert /etc/openvpn/keys/vpnserver.crt
key /etc/openvpn/keys/vpnserver.key
dh /etc/openvpn/keys/dh1024.pem

Client config:
Quote:
client
tls-client
verb 3
dev tun
proto udp
nobind
persist-key
persist-tun
ca ca.crt
cert client.crt
key client.key
remote server_ip 1194

Пробовал все, что расписано здесь:
https://community.openvpn.net/openvpn/wiki/OpenVPN_Speed