Goal: "middle boxes" are defined for this BOF as any intermediary box performing functions apart from normal, standard functions of an IP router on the data path between a source host and destination host. This includes both boxes that attempt to be transparent to application protocols, and those that participate in application protocols. Work is in progress in the IETF on some aspects of middle boxes. The BOF is intended to prepare for a structured discussion of some wider issues, from an architectural viewpoint, in order to: * Analyze issues raised by the growth of middle boxes in the Internet infrastructure. * Identify harmful and harmless practices. * Suggest architectural guidelines. * Identify additional work that should be done in the IETF and IRTF. An implied goal is to identify any necessary updates to the Architectural Principles of the Internet [RFC 1958]. The BOF will concentrate on the taxonomy presented in draft-carpenter-midtax-00.txt, as a first step in the analysis. This document establishes a taxonomy of middle boxes, cites previous or current IETF work concerning middle boxes, and attempts to identify issues and areas where further work is necessary.