RFC 2983 (rfc2983) - Page 1 of 14
Differentiated Services and Tunnels
Alternative Format: Original Text Document
Network Working Group D. Black
Request for Comments: 2983 EMC Corporation
Category: Informational October 2000
Differentiated Services and Tunnels
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
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.
1. Conventions used in this document
An IP tunnel encapsulates IP traffic in another IP header as it
passes through the tunnel; the presence of these two IP headers is a
defining characteristic of IP tunnels, although there may be
additional headers inserted between the two IP headers. The inner IP
header is that of the original traffic; an outer IP header is
attached and detached at tunnel endpoints. In general, intermediate
network nodes between tunnel endpoints operate solely on the outer IP
header, and hence diffserv-capable intermediate nodes access and
modify only the DSCP field in the outer IP header. The terms
"tunnel" and "IP tunnel" are used interchangeably in this document.
For simplicity, this document does not consider tunnels other than IP
tunnels (i.e., for which there is no encapsulating IP header), such
Black Informational