Known Content Network (CN) Request-Routing Mechanisms
RFC 3568

Document Type RFC - Informational (July 2003; No errata)
Last updated 2015-10-14
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IESG IESG state RFC 3568 (Informational)
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Responsible AD Ted Hardie
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Network Working Group                                          A. Barbir
Request for Comments: 3568                               Nortel Networks
Category: Informational                                          B. Cain
                                                        Storigen Systems
                                                                 R. Nair
                                                              Consultant
                                                           O. Spatscheck
                                                                    AT&T
                                                               July 2003

         Known Content Network (CN) Request-Routing Mechanisms

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 (2003).  All Rights Reserved.

Abstract

   This document presents a summary of Request-Routing techniques that
   are used to direct client requests to surrogates based on various
   policies and a possible set of metrics.  The document covers
   techniques that were commonly used in the industry on or before
   December 2000.  In this memo, the term Request-Routing represents
   techniques that is commonly called content routing or content
   redirection.  In principle, Request-Routing techniques can be
   classified under: DNS Request-Routing, Transport-layer
   Request-Routing, and Application-layer Request-Routing.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  DNS based Request-Routing Mechanisms . . . . . . . . . . . . 3
       2.1.  Single Reply . . . . . . . . . . . . . . . . . . . . . 3
       2.2.  Multiple Replies . . . . . . . . . . . . . . . . . . . 3
       2.3.  Multi-Level Resolution . . . . . . . . . . . . . . . . 4
             2.3.1.  NS Redirection . . . . . . . . . . . . . . . . 4
             2.3.2.  CNAME Redirection. . . . . . . . . . . . . . . 5
       2.4.  Anycast. . . . . . . . . . . . . . . . . . . . . . . . 5
       2.5.  Object Encoding. . . . . . . . . . . . . . . . . . . . 6
       2.6.  DNS Request-Routing Limitations. . . . . . . . . . . . 6
   3.  Transport-Layer Request-Routing  . . . . . . . . . . . . . . 7

Barbir, et al.               Informational                      [Page 1]
RFC 3568          Known CN Request-Routing Mechanisms          July 2003

   4.  Application-Layer Request-Routing  . . . . . . . . . . . . . 8
       4.1.  Header Inspection. . . . . . . . . . . . . . . . . . . 8
             4.1.1.  URL-Based Request-Routing. . . . . . . . . . . 8
             4.1.2.  Header-Based Request-Routing . . . . . . . . . 9
             4.1.3.  Site-Specific Identifiers. . . . . . . . . . .10
       4.2.  Content Modification . . . . . . . . . . . . . . . . .10
             4.2.1.  A-priori URL Rewriting . . . . . . . . . . . .11
             4.2.2.  On-Demand URL Rewriting. . . . . . . . . . . .11
             4.2.3.  Content Modification Limitations . . . . . . .11
   5.  Combination of Multiple Mechanisms . . . . . . . . . . . . .11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . .12
   7.  Additional Authors and Acknowledgements  . . . . . . . . . .12
   A.  Measurements . . . . . . . . . . . . . . . . . . . . . . . .13
       A.1.  Proximity Measurements . . . . . . . . . . . . . . . .13
             A.1.1.  Active Probing . . . . . . . . . . . . . . . .13
             A.1.2.  Metric Types . . . . . . . . . . . . . . . . .14
             A.1.3.  Surrogate Feedback . . . . . . . . . . . . . .14
   8.  Normative References . . . . . . . . . . . . . . . . . . . .15
   9.  Informative References . . . . . . . . . . . . . . . . . . .15
   10. Intellectual Property and Copyright Statements . . . . . . .17
   11. Authors' Addresses . . . . . . . . . . . . . . . . . . . . .18
   12. Full Copyright Statement . . . . . . . . . . . . . . . . . .19

1.  Introduction

   This document provides a summary of known request routing techniques
   that are used by the industry before December 2000.  Request routing
   techniques are generally used to direct client requests to surrogates
   based on various policies and a possible set of metrics.  The task of
   directing clients' requests to surrogates is also called
   Request-Routing, Content Routing or Content Redirection.

   Request-Routing techniques are commonly used in Content Networks
   (also known as Content Delivery Networks) [8].  Content Networks
   include network infrastructure that exists in layers 4 through 7.
   Content Networks deal with the routing and forwarding of requests and
   responses for content. Content Networks rely on layer 7 protocols
   such as HTTP [4] for transport.

   Request-Routing techniques are generally used to direct client
   requests for objects to a surrogate or a set of surrogates that could
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