Differentiated Services and Tunnels

This document considers the interaction of Differentiated Services (diffserv) (RFC 2474, RFC 2475) with IP tunnels of various forms. The discussion of tunnels in the diffserv architecture (RFC 2475) provides insufficient guidance to tunnel designers and implementers. This document describes two conceptual models for the interaction of diffserv with Internet Protocol (IP) tunnels and employs them to explore the resulting configurations and combinations of functionality. An important consideration is how and where it is appropriate to perform diffserv traffic conditioning in the presence of tunnel encapsulation and decapsulation. A few simple mechanisms are also proposed that limit the complexity that tunnels would otherwise add to the diffserv traffic conditioning model. Security considerations for IPSec tunnels limit the possible functionality in some circumstances.