Known HTTP Proxy/Caching Problems
RFC 3143

Document Type RFC - Informational (June 2001; Errata)
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Network Working Group                                          I. Cooper
Request for Comments: 3143                                 Equinix, Inc.
Category: Informational                                        J. Dilley
                                               Akamai Technologies, Inc.
                                                               June 2001

                   Known HTTP Proxy/Caching Problems

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 (2001).  All Rights Reserved.

Abstract

   This document catalogs a number of known problems with World Wide Web
   (WWW) (caching) proxies and cache servers.  The goal of the document
   is to provide a discussion of the problems and proposed workarounds,
   and ultimately to improve conditions by illustrating problems.  The
   construction of this document is a joint effort of the Web caching
   community.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  2
   1.1   Problem Template . . . . . . . . . . . . . . . . . . . . . .  2
   2.    Known Problems . . . . . . . . . . . . . . . . . . . . . . .  4
   2.1   Known Specification Problems . . . . . . . . . . . . . . . .  5
   2.1.1 Vary header is underspecified and/or misleading  . . . . . .  5
   2.1.2 Client Chaining Loses Valuable Length Meta-Data  . . . . . .  9
   2.2   Known Architectural Problems . . . . . . . . . . . . . . . . 10
   2.2.1 Interception proxies break client cache directives . . . . . 10
   2.2.2 Interception proxies prevent introduction of new HTTP
            methods  . . . . . . . . . . . . . . . . . . . . . . . .  11
   2.2.3 Interception proxies break IP address-based authentication . 12
   2.2.4 Caching proxy peer selection in heterogeneous networks . . . 13
   2.2.5 ICP Performance  . . . . . . . . . . . . . . . . . . . . . . 15
   2.2.6 Caching proxy meshes can break HTTP serialization of content 16
   2.3   Known Implementation Problems  . . . . . . . . . . . . . . . 17
   2.3.1 User agent/proxy failover  . . . . . . . . . . . . . . . . . 17
   2.3.2 Some servers send bad Content-Length headers for files that
            contain CR . . . . . . . . . . . . . . . . . . . . . . .  18

Cooper & Dilley              Informational                      [Page 1]
RFC 3143           Known HTTP Proxy/Caching Problems           June 2001

   3.    Security Considerations  . . . . . . . . . . . . . . . . . . 18
         References . . . . . . . . . . . . . . . . . . . . . . . . . 19
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20
   A.    Archived Known Problems  . . . . . . . . . . . . . . . . . . 21
   A.1   Architectural  . . . . . . . . . . . . . . . . . . . . . . . 21
   A.1.1 Cannot specify multiple URIs for replicated resources  . . . 21
   A.1.2 Replica distance is unknown  . . . . . . . . . . . . . . . . 22
   A.1.3 Proxy resource location  . . . . . . . . . . . . . . . . . . 23
   A.2   Implementation . . . . . . . . . . . . . . . . . . . . . . . 23
   A.2.1 Use of Cache-Control headers . . . . . . . . . . . . . . . . 23
   A.2.2 Lack of HTTP/1.1 compliance for caching proxies  . . . . . . 24
   A.2.3 ETag support . . . . . . . . . . . . . . . . . . . . . . . . 25
   A.2.4 Servers and content should be optimized for caching  . . . . 26
   A.3   Administration . . . . . . . . . . . . . . . . . . . . . . . 27
   A.3.1 Lack of fine-grained, standardized hierarchy controls  . . . 27
   A.3.2 Proxy/Server exhaustive log format standard for analysis . . 27
   A.3.3 Trace log timestamps . . . . . . . . . . . . . . . . . . . . 28
   A.3.4 Exchange format for log summaries  . . . . . . . . . . . . . 29
         Full Copyright Statement . . . . . . . . . . . . . . . . . . 32

1. Introduction

   This memo discusses problems with proxies - which act as
   application-level intermediaries for Web requests - and more
   specifically with caching proxies, which retain copies of previously
   requested resources in the hope of improving overall quality of
   service by serving the content locally.  Commonly used terminology in
   this memo can be found in the "Internet Web Replication and Caching
   Taxonomy"[2].

   No individual or organization has complete knowledge of the known
   problems in Web caching, and the editors are grateful to the
   contributors to this document.

1.1 Problem Template

   A common problem template is used within the following sections.  We
   gratefully acknowledge RFC2525 [1] which helped define an initial
   format for this known problems list.  The template format is
   summarized in the following table and described in more detail below.

      Name:           short, descriptive name of the problem (3-5 words)
      Classification: classifies the problem: performance, security, etc
      Description:    describes the problem succinctly
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