OpenVPN + Scrambled patch on Amazon EC2

Question

Yesterday I deployed a regular OpenVPN installation on Debian Squeeze / Amazon EC2. The VPN server is in Singapore and I connect to it from China Mainland. Later on, after some tests I had to start thinking on patching OpenVPN with the "Scrambled" patch, to enable packet scrambling so I avoid the Great Firewall blocking my UPD packets.

I compiled today from source said patch + OpenVPN, on a M3 Instance ( exactly as yesterday ) and now the connection is stable but I have terrible latency. yesterday I had 80ms when pinging the tun interface of the server and today I have an stable fat 270ms.

Is it possible that the packet scrambling adds a lot of overhead and thus, getting this terrible latency inflation ? Or do you think there could be more issues ? The configuration is exactly as the one I made for the server yesterday.

port 443
proto udp
dev tun
scramble obfuscate guardian
ca /etc/openvpn/ca.crt
cert /etc/openvpn/elmer.crt
key /etc/openvpn/elmer.key
tls-auth /etc/openvpn/ta.key 0
dh /etc/openvpn/dh2048.pem
server 10.8.0.0 255.255.255.0
cipher DES-EDE3-CBC
comp-lzo
tun-mtu 1300
persist-key
persist-tun
user www-data       
group www-data  
status openvpn-status.log
verb 3

CLIENT CONFIG :

client
dev tun
scramble obfuscate guardian
proto udp
remote xx.xx.xx.xx 443
resolv-retry infinite
nobind
persist-key
persist-tun
ca ca.crt
cert beijing.crt
key beijing.key
tls-auth ta.key 1
ns-cert-type server
cipher DES-EDE3-CBC
comp-lzo
verb 3
fast-io
script-security 2

Answer 1

The scramble patch adds no communication overhead (the packet size doesn't change) and negligible CPU overhead. Your issues are caused by the unpredictable nature of China's connectivity to the outside world. I advise that you move the vpn to a different location. Japan, Korea, Hong Kong and Taiwan should work much better.