TPOT: translucent proxying of TCP

Transparent Layer-4 proxies are being widely deployed in the current Internet to enable a vast variety of applications. These include Web proxy caching, transcoding, service differentiation, and load balancing. To ensure that all IP packets of an intercepted TCP connection are seen by the intercepting transparent proxy, they must sit at focal points in the network. Translucent Proxying of TCP (TPOT) overcomes this limitation by using TCP options and IP tunneling to ensure that all IP packets belonging to a TCP connection will traverse the proxy that intercepted the first packet. This guarantee allows the ad-hoc deployment of TPOT proxies anywhere within the network. No extra signaling support is required for its correct functioning. In addition to the advantages TPOT proxies offer at the application level, they also usually improve the throughput of intercepted TCP connections. In this paper we discuss the TPOT protocol, explain how it enables various applications, describe a prototype implementation, analyze its impact on the performance of TCP, and address scalability issues.