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. Once the new packet is received, the packet order is restored. Until that time, all packets after the lost packet are on hold. The problem with tunnelling TCP traffic over a TCP connection is that both layers want to guarantee ordered packet delivery...