OpenVPN Cookbook - Second Edition

Tuning TCP-based connections

In this recipe, we focus on some of the basic techniques for optimizing TCP-based VPN tunnels. In a TCP-based VPN setup, the connection between the VPN endpoints is a regular TCP connection. This has advantages and drawbacks. The main advantage is that it is often easier to set up a TCP connection than a UDP connection, mostly due to firewall restrictions. The main drawback of tunneling TCP traffic over a TCP-based tunnel is that there is chance of severe performance penalties, especially when the network connection is poor. This performance penalty is caused by the tcp-over-tcp syndrome. The TCP protocol guarantees the ordered delivery of packets, thus if a packet is dropped along the way, the packet will be resent. ...