Cisco Systems' Tag Switching Architecture Overview
RFC 2105

Document Type RFC - Informational (February 1997; No errata)
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Last updated 2013-03-02
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Network Working Group                                         Y. Rekhter
Request for Comments: 2105                                      B. Davie
Category: Informational                                          D. Katz
                                                                E. Rosen
                                                              G. Swallow
                                                     Cisco Systems, Inc.
                                                           February 1997

           Cisco Systems' Tag Switching Architecture Overview

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

IESG Note:

   This protocol is NOT the product of an IETF working group nor is it a
   standards track document.  It has not necessarily benefited from the
   widespread and in depth community review that standards track
   documents receive.

Abstract

   This document provides an overview of a novel approach to network
   layer packet forwarding, called tag switching. The two main
   components of  the tag switching architecture - forwarding and
   control - are described.  Forwarding is accomplished using simple
   label-swapping techniques, while the existing network layer routing
   protocols plus mechanisms for binding and distributing tags are used
   for control. Tag switching can retain the scaling properties of IP,
   and can help improve the scalability of IP networks. While tag
   switching does not rely on ATM, it can straightforwardly be applied
   to ATM switches. A range of tag switching applications and deployment
   scenarios are described.

Table of Contents

   1      Introduction  ...........................................   2
   2      Tag Switching components  ...............................   3
   3      Forwarding component  ...................................   3
   3.1    Tag encapsulation  ......................................   4
   4      Control component  ......................................   4
   4.1    Destination-based routing  ..............................   5
   4.2    Hierarchy of routing knowledge  .........................   7
   4.3    Multicast  ..............................................   8

Rekhter, et. al.             Informational                      [Page 1]
RFC 2105           Cisco's Tag Switching Architecture      February 1997

   4.4    Flexible routing (explicit routes)  .....................   9
   5      Tag switching with ATM  .................................   9
   6      Quality of service  .....................................  11
   7      Tag switching migration strategies  .....................  11
   8      Summary  ................................................  12
   9      Security Considerations  ................................  12
   10     Intellectual Property Considerations  ...................  12
   11     Acknowledgments  ........................................  12
   12     Authors' Addresses  .....................................  13

1. Introduction

   Continuous growth of the Internet demands higher bandwidth within the
   Internet Service Providers (ISPs). However, growth of the Internet is
   not the only driving factor for higher bandwidth - demand for higher
   bandwidth also comes from emerging multimedia applications.  Demand
   for higher bandwidth, in turn, requires higher forwarding performance
   (packets per second) by routers, for both multicast and unicast
   traffic.

   The growth of the Internet also demands improved scaling properties
   of the Internet routing system. The ability to contain the volume of
   routing information maintained by individual routers and the ability
   to build a hierarchy of routing knowledge are essential to support a
   high quality, scalable routing system.

   We see the need to improve forwarding performance while at the same
   time adding routing functionality to support multicast, allowing more
   flexible control over how traffic is routed, and providing the
   ability to build a hierarchy of routing knowledge. Moreover, it
   becomes more and more crucial to have a routing system that can
   support graceful evolution to accommodate new and emerging
   requirements.

   Tag switching is a technology that provides an efficient solution to
   these challenges. Tag switching blends the flexibility and rich
   functionality provided by Network Layer routing with the simplicity
   provided by the label swapping forwarding paradigm.  The simplicity
   of the tag switching forwarding paradigm (label swapping) enables
   improved forwarding performance, while maintaining competitive
   price/performance.  By associating a wide range of forwarding
   granularities with a tag, the same forwarding paradigm can be used to
   support a wide variety of routing functions, such as destination-
   based routing, multicast, hierarchy of routing knowledge, and
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