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| 4 |
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| 5 |
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| 6 |
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| 7 | Network Working Group I. Cooper
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| 8 | Request for Comments: 3040 Equinix, Inc.
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| 9 | Category: Informational I. Melve
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| 10 | UNINETT
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| 11 | G. Tomlinson
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| 12 | CacheFlow Inc.
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| 13 | January 2001
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| 14 |
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| 15 |
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| 16 | Internet Web Replication and Caching Taxonomy
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| 17 |
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| 18 | Status of this Memo
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| 19 |
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| 20 | This memo provides information for the Internet community. It does
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| 21 | not specify an Internet standard of any kind. Distribution of this
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| 22 | memo is unlimited.
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| 23 |
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| 24 | Copyright Notice
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| 25 |
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| 26 | Copyright (C) The Internet Society (2001). All Rights Reserved.
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| 27 |
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| 28 | Abstract
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| 29 |
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| 30 | This memo specifies standard terminology and the taxonomy of web
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| 31 | replication and caching infrastructure as deployed today. It
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| 32 | introduces standard concepts, and protocols used today within this
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| 33 | application domain. Currently deployed solutions employing these
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| 34 | technologies are presented to establish a standard taxonomy. Known
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| 35 | problems with caching proxies are covered in the document titled
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| 36 | "Known HTTP Proxy/Caching Problems", and are not part of this
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| 37 | document. This document presents open protocols and points to
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| 38 | published material for each protocol.
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| 39 |
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| 40 | Table of Contents
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| 41 |
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| 42 | 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
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| 43 | 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
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| 44 | 2.1 Base Terms . . . . . . . . . . . . . . . . . . . . . . . . 4
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| 45 | 2.2 First order derivative terms . . . . . . . . . . . . . . . 6
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| 46 | 2.3 Second order derivatives . . . . . . . . . . . . . . . . . 7
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| 47 | 2.4 Topological terms . . . . . . . . . . . . . . . . . . . . 7
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| 48 | 2.5 Automatic use of proxies . . . . . . . . . . . . . . . . . 8
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| 49 | 3. Distributed System Relationships . . . . . . . . . . . . . 9
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| 50 | 3.1 Replication Relationships . . . . . . . . . . . . . . . . 9
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| 51 | 3.1.1 Client to Replica . . . . . . . . . . . . . . . . . . . . 9
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| 52 | 3.1.2 Inter-Replica . . . . . . . . . . . . . . . . . . . . . . 9
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| 53 | 3.2 Proxy Relationships . . . . . . . . . . . . . . . . . . . 10
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| 54 | 3.2.1 Client to Non-Interception Proxy . . . . . . . . . . . . . 10
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| 55 |
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| 56 |
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| 57 |
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| 58 | Cooper, et al. Informational [Page 1]
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| 59 | |
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| 60 |
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| 61 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 62 |
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| 63 |
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| 64 | 3.2.2 Client to Surrogate to Origin Server . . . . . . . . . . . 10
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| 65 | 3.2.3 Inter-Proxy . . . . . . . . . . . . . . . . . . . . . . . 11
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| 66 | 3.2.3.1 (Caching) Proxy Meshes . . . . . . . . . . . . . . . . . . 11
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| 67 | 3.2.3.2 (Caching) Proxy Arrays . . . . . . . . . . . . . . . . . . 12
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| 68 | 3.2.4 Network Element to Caching Proxy . . . . . . . . . . . . . 12
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| 69 | 4. Replica Selection . . . . . . . . . . . . . . . . . . . . 13
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| 70 | 4.1 Navigation Hyperlinks . . . . . . . . . . . . . . . . . . 13
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| 71 | 4.2 Replica HTTP Redirection . . . . . . . . . . . . . . . . . 14
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| 72 | 4.3 DNS Redirection . . . . . . . . . . . . . . . . . . . . . 14
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| 73 | 5. Inter-Replica Communication . . . . . . . . . . . . . . . 15
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| 74 | 5.1 Batch Driven Replication . . . . . . . . . . . . . . . . . 15
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| 75 | 5.2 Demand Driven Replication . . . . . . . . . . . . . . . . 16
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| 76 | 5.3 Synchronized Replication . . . . . . . . . . . . . . . . . 16
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| 77 | 6. User Agent to Proxy Configuration . . . . . . . . . . . . 17
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| 78 | 6.1 Manual Proxy Configuration . . . . . . . . . . . . . . . . 17
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| 79 | 6.2 Proxy Auto Configuration (PAC) . . . . . . . . . . . . . . 17
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| 80 | 6.3 Cache Array Routing Protocol (CARP) v1.0 . . . . . . . . . 18
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| 81 | 6.4 Web Proxy Auto-Discovery Protocol (WPAD) . . . . . . . . . 18
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| 82 | 7. Inter-Proxy Communication . . . . . . . . . . . . . . . . 19
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| 83 | 7.1 Loosely coupled Inter-Proxy Communication . . . . . . . . 19
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| 84 | 7.1.1 Internet Cache Protocol (ICP) . . . . . . . . . . . . . . 19
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| 85 | 7.1.2 Hyper Text Caching Protocol . . . . . . . . . . . . . . . 20
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| 86 | 7.1.3 Cache Digest . . . . . . . . . . . . . . . . . . . . . . . 21
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| 87 | 7.1.4 Cache Pre-filling . . . . . . . . . . . . . . . . . . . . 22
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| 88 | 7.2 Tightly Coupled Inter-Cache Communication . . . . . . . . 22
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| 89 | 7.2.1 Cache Array Routing Protocol (CARP) v1.0 . . . . . . . . . 22
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| 90 | 8. Network Element Communication . . . . . . . . . . . . . . 23
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| 91 | 8.1 Web Cache Control Protocol (WCCP) . . . . . . . . . . . . 23
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| 92 | 8.2 Network Element Control Protocol (NECP) . . . . . . . . . 24
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| 93 | 8.3 SOCKS . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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| 94 | 9. Security Considerations . . . . . . . . . . . . . . . . . 25
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| 95 | 9.1 Authentication . . . . . . . . . . . . . . . . . . . . . . 26
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| 96 | 9.1.1 Man in the middle attacks . . . . . . . . . . . . . . . . 26
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| 97 | 9.1.2 Trusted third party . . . . . . . . . . . . . . . . . . . 26
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| 98 | 9.1.3 Authentication based on IP number . . . . . . . . . . . . 26
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| 99 | 9.2 Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 26
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| 100 | 9.2.1 Trusted third party . . . . . . . . . . . . . . . . . . . 26
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| 101 | 9.2.2 Logs and legal implications . . . . . . . . . . . . . . . 27
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| 102 | 9.3 Service security . . . . . . . . . . . . . . . . . . . . . 27
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| 103 | 9.3.1 Denial of service . . . . . . . . . . . . . . . . . . . . 27
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| 104 | 9.3.2 Replay attack . . . . . . . . . . . . . . . . . . . . . . 27
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| 105 | 9.3.3 Stupid configuration of proxies . . . . . . . . . . . . . 28
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| 106 | 9.3.4 Copyrighted transient copies . . . . . . . . . . . . . . . 28
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| 107 | 9.3.5 Application level access . . . . . . . . . . . . . . . . . 28
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| 108 | 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 28
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| 109 | References . . . . . . . . . . . . . . . . . . . . . . . . 28
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| 110 | Authors' Addresses . . . . . . . . . . . . . . . . . . . . 31
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| 111 | Full Copyright Statement . . . . . . . . . . . . . . . . . 32
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| 112 |
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| 113 |
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| 114 |
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| 115 | Cooper, et al. Informational [Page 2]
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| 116 | |
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| 117 |
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| 118 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 119 |
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| 120 |
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| 121 | 1. Introduction
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| 122 |
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| 123 | Since its introduction in 1990, the World-Wide Web has evolved from a
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| 124 | simple client server model into a complex distributed architecture.
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| 125 | This evolution has been driven largely due to the scaling problems
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| 126 | associated with exponential growth. Distinct paradigms and solutions
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| 127 | have emerged to satisfy specific requirements. Two core
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| 128 | infrastructure components being employed to meet the demands of this
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| 129 | growth are replication and caching. In many cases, there is a need
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| 130 | for web caches and replicated services to be able to coexist.
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| 131 |
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| 132 | This memo specifies standard terminology and the taxonomy of web
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| 133 | replication and caching infrastructure deployed in the Internet
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| 134 | today. The principal goal of this document is to establish a common
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| 135 | understanding and reference point of this application domain.
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| 136 |
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| 137 | It is also expected that this document will be used in the creation
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| 138 | of a standard architectural framework for efficient, reliable, and
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| 139 | predictable service in a web which includes both replicas and caches.
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| 140 |
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| 141 | Some of the protocols which this memo examines are specified only by
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| 142 | company technical white papers or work in progress documents. Such
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| 143 | references are included to demonstrate the existence of such
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| 144 | protocols, their experimental deployment in the Internet today, or to
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| 145 | aid the reader in their understanding of this technology area.
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| 146 |
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| 147 | There are many protocols, both open and proprietary, employed in web
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| 148 | replication and caching today. A majority of the open protocols
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| 149 | include DNS [8], Cache Digests [21][10], CARP [14], HTTP [1], ICP
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| 150 | [2], PAC [12], SOCKS [7], WPAD [13], and WCCP [18][19]. These
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| 151 | protocols, and their use within the caching and replication
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| 152 | environments, are discussed below.
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| 153 |
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| 154 | 2. Terminology
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| 155 |
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| 156 | The following terminology provides definitions of common terms used
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| 157 | within the web replication and caching community. Base terms are
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| 158 | taken, where possible, from the HTTP/1.1 specification [1] and are
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| 159 | included here for reference. First- and second-order derivatives are
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| 160 | constructed from these base terms to help define the relationships
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| 161 | that exist within this area.
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| 162 |
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| 163 | Terms that are in common usage and which are contrary to definitions
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| 164 | in RFC 2616 and this document are highlighted.
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| 165 |
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| 166 |
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| 167 |
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| 168 |
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| 169 |
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| 170 |
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| 171 |
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| 172 | Cooper, et al. Informational [Page 3]
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| 173 | |
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| 174 |
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| 175 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 176 |
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| 177 |
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| 178 | 2.1 Base Terms
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| 179 |
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| 180 | The majority of these terms are taken as-is from RFC 2616 [1], and
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| 181 | are included here for reference.
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| 182 |
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| 183 | client (taken from [1])
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| 184 | A program that establishes connections for the purpose of sending
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| 185 | requests.
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| 186 |
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| 187 | server (taken from [1])
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| 188 | An application program that accepts connections in order to
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| 189 | service requests by sending back responses. Any given program may
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| 190 | be capable of being both a client and a server; our use of these
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| 191 | terms refers only to the role being performed by the program for a
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| 192 | particular connection, rather than to the program's capabilities
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| 193 | in general. Likewise, any server may act as an origin server,
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| 194 | proxy, gateway, or tunnel, switching behavior based on the nature
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| 195 | of each request.
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| 196 |
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| 197 | proxy (taken from [1])
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| 198 | An intermediary program which acts as both a server and a client
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| 199 | for the purpose of making requests on behalf of other clients.
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| 200 | Requests are serviced internally or by passing them on, with
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| 201 | possible translation, to other servers. A proxy MUST implement
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| 202 | both the client and server requirements of this specification. A
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| 203 | "transparent proxy" is a proxy that does not modify the request or
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| 204 | response beyond what is required for proxy authentication and
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| 205 | identification. A "non-transparent proxy" is a proxy that
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| 206 | modifies the request or response in order to provide some added
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| 207 | service to the user agent, such as group annotation services,
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| 208 | media type transformation, protocol reduction, or anonymity
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| 209 | filtering. Except where either transparent or non-transparent
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| 210 | behavior is explicitly stated, the HTTP proxy requirements apply
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| 211 | to both types of proxies.
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| 212 |
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| 213 | Note: The term "transparent proxy" refers to a semantically
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| 214 | transparent proxy as described in [1], not what is commonly
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| 215 | understood within the caching community. We recommend that the term
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| 216 | "transparent proxy" is always prefixed to avoid confusion (e.g.,
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| 217 | "network transparent proxy"). However, see definition of
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| 218 | "interception proxy" below.
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| 219 |
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| 220 | The above condition requiring implementation of both the server and
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| 221 | client requirements of HTTP/1.1 is only appropriate for a non-network
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| 222 | transparent proxy.
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| 223 |
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| 224 |
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| 225 |
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| 226 |
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| 227 |
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| 228 |
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| 229 | Cooper, et al. Informational [Page 4]
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| 230 | |
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| 231 |
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| 232 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 233 |
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| 234 |
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| 235 | cache (taken from [1])
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| 236 | A program's local store of response messages and the subsystem
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| 237 | that controls its message storage, retrieval, and deletion. A
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| 238 | cache stores cacheable responses in order to reduce the response
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| 239 | time and network bandwidth consumption on future, equivalent
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| 240 | requests. Any client or server may include a cache, though a
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| 241 | cache cannot be used by a server that is acting as a tunnel.
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| 242 |
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| 243 | Note: The term "cache" used alone often is meant as "caching proxy".
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| 244 |
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| 245 | Note: There are additional motivations for caching, for example
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| 246 | reducing server load (as a further means to reduce response time).
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| 247 |
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| 248 | cacheable (taken from [1])
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| 249 | A response is cacheable if a cache is allowed to store a copy of
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| 250 | the response message for use in answering subsequent requests.
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| 251 | The rules for determining the cacheability of HTTP responses are
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| 252 | defined in section 13. Even if a resource is cacheable, there may
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| 253 | be additional constraints on whether a cache can use the cached
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| 254 | copy for a particular request.
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| 255 |
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| 256 | gateway (taken from [1])
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| 257 | A server which acts as an intermediary for some other server.
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| 258 | Unlike a proxy, a gateway receives requests as if it were the
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| 259 | origin server for the requested resource; the requesting client
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| 260 | may not be aware that it is communicating with a gateway.
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| 261 |
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| 262 | tunnel (taken from [1])
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| 263 | An intermediary program which is acting as a blind relay between
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| 264 | two connections. Once active, a tunnel is not considered a party
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| 265 | to the HTTP communication, though the tunnel may have been
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| 266 | initiated by an HTTP request. The tunnel ceases to exist when
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| 267 | both ends of the relayed connections are closed.
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| 268 |
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| 269 | replication
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| 270 | "Creating and maintaining a duplicate copy of a database or file
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| 271 | system on a different computer, typically a server." - Free
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| 272 | Online Dictionary of Computing (FOLDOC)
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| 273 |
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| 274 | inbound/outbound (taken from [1])
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| 275 | Inbound and outbound refer to the request and response paths for
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| 276 | messages: "inbound" means "traveling toward the origin server",
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| 277 | and "outbound" means "traveling toward the user agent".
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| 278 |
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| 279 | network element
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| 280 | A network device that introduces multiple paths between source and
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| 281 | destination, transparent to HTTP.
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| 282 |
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| 283 |
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| 284 |
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| 285 |
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| 286 | Cooper, et al. Informational [Page 5]
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| 287 | |
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| 288 |
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| 289 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 290 |
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| 291 |
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| 292 | 2.2 First order derivative terms
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| 293 |
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| 294 | The following terms are constructed taking the above base terms as
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| 295 | foundation.
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| 296 |
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| 297 | origin server (taken from [1])
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| 298 | The server on which a given resource resides or is to be created.
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| 299 |
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| 300 | user agent (taken from [1])
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| 301 | The client which initiates a request. These are often browsers,
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| 302 | editors, spiders (web-traversing robots), or other end user tools.
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| 303 |
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| 304 | caching proxy
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| 305 | A proxy with a cache, acting as a server to clients, and a client
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| 306 | to servers.
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| 307 |
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| 308 | Caching proxies are often referred to as "proxy caches" or simply
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| 309 | "caches". The term "proxy" is also frequently misused when
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| 310 | referring to caching proxies.
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| 311 |
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| 312 | surrogate
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| 313 | A gateway co-located with an origin server, or at a different
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| 314 | point in the network, delegated the authority to operate on behalf
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| 315 | of, and typically working in close co-operation with, one or more
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| 316 | origin servers. Responses are typically delivered from an
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| 317 | internal cache.
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| 318 |
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| 319 | Surrogates may derive cache entries from the origin server or from
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| 320 | another of the origin server's delegates. In some cases a
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| 321 | surrogate may tunnel such requests.
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| 322 |
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| 323 | Where close co-operation between origin servers and surrogates
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| 324 | exists, this enables modifications of some protocol requirements,
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| 325 | including the Cache-Control directives in [1]. Such modifications
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| 326 | have yet to be fully specified.
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| 327 |
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| 328 | Devices commonly known as "reverse proxies" and "(origin) server
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| 329 | accelerators" are both more properly defined as surrogates.
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| 330 |
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| 331 | reverse proxy
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| 332 | See "surrogate".
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| 333 |
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| 334 | server accelerator
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| 335 | See "surrogate".
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| 336 |
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| 337 |
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| 338 |
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| 339 |
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| 340 |
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| 341 |
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| 342 |
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| 343 | Cooper, et al. Informational [Page 6]
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| 344 | |
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| 345 |
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| 346 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
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| 347 |
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| 348 |
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| 349 | 2.3 Second order derivatives
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| 350 |
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| 351 | The following terms further build on first order derivatives:
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| 352 |
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| 353 | master origin server
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| 354 | An origin server on which the definitive version of a resource
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| 355 | resides.
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| 356 |
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| 357 | replica origin server
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| 358 | An origin server holding a replica of a resource, but which may
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| 359 | act as an authoritative reference for client requests.
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| 360 |
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| 361 | content consumer
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| 362 | The user or system that initiates inbound requests, through use of
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| 363 | a user agent.
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| 364 |
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| 365 | browser
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| 366 | A special instance of a user agent that acts as a content
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| 367 | presentation device for content consumers.
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| 368 |
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| 369 | 2.4 Topological terms
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| 370 |
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| 371 | The following definitions are added to describe caching device
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| 372 | topology:
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| 373 |
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| 374 | user agent cache
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| 375 | The cache within the user agent program.
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| 376 |
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| 377 | local caching proxy
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| 378 | The caching proxy to which a user agent connects.
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| 379 |
|
|---|
| 380 | intermediate caching proxy
|
|---|
| 381 | Seen from the content consumer's view, all caches participating in
|
|---|
| 382 | the caching mesh that are not the user agent's local caching
|
|---|
| 383 | proxy.
|
|---|
| 384 |
|
|---|
| 385 | cache server
|
|---|
| 386 | A server to requests made by local and intermediate caching
|
|---|
| 387 | proxies, but which does not act as a proxy.
|
|---|
| 388 |
|
|---|
| 389 | cache array
|
|---|
| 390 | A cluster of caching proxies, acting logically as one service and
|
|---|
| 391 | partitioning the resource name space across the array. Also known
|
|---|
| 392 | as "diffused array" or "cache cluster".
|
|---|
| 393 |
|
|---|
| 394 |
|
|---|
| 395 |
|
|---|
| 396 |
|
|---|
| 397 |
|
|---|
| 398 |
|
|---|
| 399 |
|
|---|
| 400 | Cooper, et al. Informational [Page 7]
|
|---|
| 401 | |
|---|
| 402 |
|
|---|
| 403 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 404 |
|
|---|
| 405 |
|
|---|
| 406 | caching mesh
|
|---|
| 407 | a loosely coupled set of co-operating proxy- and (optionally)
|
|---|
| 408 | caching-servers, or clusters, acting independently but sharing
|
|---|
| 409 | cacheable content between themselves using inter-cache
|
|---|
| 410 | communication protocols.
|
|---|
| 411 |
|
|---|
| 412 | 2.5 Automatic use of proxies
|
|---|
| 413 |
|
|---|
| 414 | Network administrators may wish to force or facilitate the use of
|
|---|
| 415 | proxies by clients, enabling such configuration within the network
|
|---|
| 416 | itself or within automatic systems in user agents, such that the
|
|---|
| 417 | content consumer need not be aware of any such configuration issues.
|
|---|
| 418 |
|
|---|
| 419 | The terms that describe such configurations are given below.
|
|---|
| 420 |
|
|---|
| 421 | automatic user-agent proxy configuration
|
|---|
| 422 | The technique of discovering the availability of one or more
|
|---|
| 423 | proxies and the automated configuration of the user agent to use
|
|---|
| 424 | them. The use of a proxy is transparent to the content consumer
|
|---|
| 425 | but not to the user agent. The term "automatic proxy
|
|---|
| 426 | configuration" is also used in this sense.
|
|---|
| 427 |
|
|---|
| 428 | traffic interception
|
|---|
| 429 | The process of using a network element to examine network traffic
|
|---|
| 430 | to determine whether it should be redirected.
|
|---|
| 431 |
|
|---|
| 432 | traffic redirection
|
|---|
| 433 | Redirection of client requests from a network element performing
|
|---|
| 434 | traffic interception to a proxy. Used to deploy (caching) proxies
|
|---|
| 435 | without the need to manually reconfigure individual user agents,
|
|---|
| 436 | or to force the use of a proxy where such use would not otherwise
|
|---|
| 437 | occur.
|
|---|
| 438 |
|
|---|
| 439 | interception proxy (a.k.a. "transparent proxy", "transparent cache")
|
|---|
| 440 | The term "transparent proxy" has been used within the caching
|
|---|
| 441 | community to describe proxies used with zero configuration within
|
|---|
| 442 | the user agent. Such use is somewhat transparent to user agents.
|
|---|
| 443 | Due to discrepancies with [1] (see definition of "proxy" above),
|
|---|
| 444 | and objections to the use of the word "transparent", we introduce
|
|---|
| 445 | the term "interception proxy" to describe proxies that receive
|
|---|
| 446 | redirected traffic flows from network elements performing traffic
|
|---|
| 447 | interception.
|
|---|
| 448 |
|
|---|
| 449 | Interception proxies receive inbound traffic flows through the
|
|---|
| 450 | process of traffic redirection. (Such proxies are deployed by
|
|---|
| 451 | network administrators to facilitate or require the use of
|
|---|
| 452 | appropriate services offered by the proxy). Problems associated
|
|---|
| 453 | with the deployment of interception proxies are described in the
|
|---|
| 454 |
|
|---|
| 455 |
|
|---|
| 456 |
|
|---|
| 457 | Cooper, et al. Informational [Page 8]
|
|---|
| 458 | |
|---|
| 459 |
|
|---|
| 460 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 461 |
|
|---|
| 462 |
|
|---|
| 463 | document "Known HTTP Proxy/Caching Problems" [23]. The use of
|
|---|
| 464 | interception proxies requires zero configuration of the user agent
|
|---|
| 465 | which act as though communicating directly with an origin server.
|
|---|
| 466 |
|
|---|
| 467 | 3. Distributed System Relationships
|
|---|
| 468 |
|
|---|
| 469 | This section identifies the relationships that exist in a distributed
|
|---|
| 470 | replication and caching environment. Having defined these
|
|---|
| 471 | relationships, later sections describe the communication protocols
|
|---|
| 472 | used in each relationship.
|
|---|
| 473 |
|
|---|
| 474 | 3.1 Replication Relationships
|
|---|
| 475 |
|
|---|
| 476 | The following sections describe relationships between clients and
|
|---|
| 477 | replicas and between replicas themselves.
|
|---|
| 478 |
|
|---|
| 479 | 3.1.1 Client to Replica
|
|---|
| 480 |
|
|---|
| 481 | A client may communicate with one or more replica origin servers, as
|
|---|
| 482 | well as with master origin servers. (In the absence of replica
|
|---|
| 483 | servers the client interacts directly with the origin server as is
|
|---|
| 484 | the normal case.)
|
|---|
| 485 |
|
|---|
| 486 | ------------------ ----------------- ------------------
|
|---|
| 487 | | Replica Origin | | Master Origin | | Replica Origin |
|
|---|
| 488 | | Server | | Server | | Server |
|
|---|
| 489 | ------------------ ----------------- ------------------
|
|---|
| 490 | \ | /
|
|---|
| 491 | \ | /
|
|---|
| 492 | -----------------------------------------
|
|---|
| 493 | | Client to
|
|---|
| 494 | ----------------- Replica Server
|
|---|
| 495 | | Client |
|
|---|
| 496 | -----------------
|
|---|
| 497 |
|
|---|
| 498 | Protocols used to enable the client to use one of the replicas can be
|
|---|
| 499 | found in Section 4.
|
|---|
| 500 |
|
|---|
| 501 | 3.1.2 Inter-Replica
|
|---|
| 502 |
|
|---|
| 503 | This is the relationship between master origin server(s) and replica
|
|---|
| 504 | origin servers, to replicate data sets that are accessed by clients
|
|---|
| 505 | in the relationship shown in Section 3.1.1.
|
|---|
| 506 |
|
|---|
| 507 |
|
|---|
| 508 |
|
|---|
| 509 |
|
|---|
| 510 |
|
|---|
| 511 |
|
|---|
| 512 |
|
|---|
| 513 |
|
|---|
| 514 | Cooper, et al. Informational [Page 9]
|
|---|
| 515 | |
|---|
| 516 |
|
|---|
| 517 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 518 |
|
|---|
| 519 |
|
|---|
| 520 | ------------------ ----------------- ------------------
|
|---|
| 521 | | Replica Origin |-----| Master Origin |-----| Replica Origin |
|
|---|
| 522 | | Server | | Server | | Server |
|
|---|
| 523 | ------------------ ----------------- ------------------
|
|---|
| 524 |
|
|---|
| 525 | Protocols used in this relationship can be found in Section 5.
|
|---|
| 526 |
|
|---|
| 527 | 3.2 Proxy Relationships
|
|---|
| 528 |
|
|---|
| 529 | There are a variety of ways in which (caching) proxies and cache
|
|---|
| 530 | servers communicate with each other, and with user agents.
|
|---|
| 531 |
|
|---|
| 532 | 3.2.1 Client to Non-Interception Proxy
|
|---|
| 533 |
|
|---|
| 534 | A client may communicate with zero or more proxies for some or all
|
|---|
| 535 | requests. Where the result of communication results in no proxy
|
|---|
| 536 | being used, the relationship is between client and (replica) origin
|
|---|
| 537 | server (see Section 3.1.1).
|
|---|
| 538 |
|
|---|
| 539 | ----------------- ----------------- -----------------
|
|---|
| 540 | | Local | | Local | | Local |
|
|---|
| 541 | | Proxy | | Proxy | | Proxy |
|
|---|
| 542 | ----------------- ----------------- -----------------
|
|---|
| 543 | \ | /
|
|---|
| 544 | \ | /
|
|---|
| 545 | -----------------------------------------
|
|---|
| 546 | |
|
|---|
| 547 | -----------------
|
|---|
| 548 | | Client |
|
|---|
| 549 | -----------------
|
|---|
| 550 |
|
|---|
| 551 | In addition, a user agent may interact with an additional server -
|
|---|
| 552 | operated on behalf of a proxy for the purpose of automatic user agent
|
|---|
| 553 | proxy configuration.
|
|---|
| 554 |
|
|---|
| 555 | Schemes and protocols used in these relationships can be found in
|
|---|
| 556 | Section 6.
|
|---|
| 557 |
|
|---|
| 558 | 3.2.2 Client to Surrogate to Origin Server
|
|---|
| 559 |
|
|---|
| 560 | A client may communicate with zero or more surrogates for requests
|
|---|
| 561 | intended for one or more origin servers. Where a surrogate is not
|
|---|
| 562 | used, the client communicates directly with an origin server. Where
|
|---|
| 563 | a surrogate is used the client communicates as if with an origin
|
|---|
| 564 | server. The surrogate fulfills the request from its internal cache,
|
|---|
| 565 | or acts as a gateway or tunnel to the origin server.
|
|---|
| 566 |
|
|---|
| 567 |
|
|---|
| 568 |
|
|---|
| 569 |
|
|---|
| 570 |
|
|---|
| 571 | Cooper, et al. Informational [Page 10]
|
|---|
| 572 | |
|---|
| 573 |
|
|---|
| 574 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 575 |
|
|---|
| 576 |
|
|---|
| 577 | -------------- -------------- --------------
|
|---|
| 578 | | Origin | | Origin | | Origin |
|
|---|
| 579 | | Server | | Server | | Server |
|
|---|
| 580 | -------------- -------------- --------------
|
|---|
| 581 | \ | /
|
|---|
| 582 | \ | /
|
|---|
| 583 | -----------------
|
|---|
| 584 | | Surrogate |
|
|---|
| 585 | | |
|
|---|
| 586 | -----------------
|
|---|
| 587 | |
|
|---|
| 588 | |
|
|---|
| 589 | ------------
|
|---|
| 590 | | Client |
|
|---|
| 591 | ------------
|
|---|
| 592 |
|
|---|
| 593 | 3.2.3 Inter-Proxy
|
|---|
| 594 |
|
|---|
| 595 | Inter-Proxy relationships exist as meshes (loosely coupled) and
|
|---|
| 596 | clusters (tightly coupled).
|
|---|
| 597 |
|
|---|
| 598 | 3.2.3.1 (Caching) Proxy Meshes
|
|---|
| 599 |
|
|---|
| 600 | Within a loosely coupled mesh of (caching) proxies, communication can
|
|---|
| 601 | happen at the same level between peers, and with one or more parents.
|
|---|
| 602 |
|
|---|
| 603 | --------------------- ---------------------
|
|---|
| 604 | -----------| Intermediate | | Intermediate |
|
|---|
| 605 | | | Caching Proxy (D) | | Caching Proxy (E) |
|
|---|
| 606 | |(peer) --------------------- ---------------------
|
|---|
| 607 | -------------- | (parent) / (parent)
|
|---|
| 608 | | Cache | | ------/
|
|---|
| 609 | | Server (C) | | /
|
|---|
| 610 | -------------- | /
|
|---|
| 611 | (peer) | ----------------- ---------------------
|
|---|
| 612 | -------------| Local Caching |-------| Intermediate |
|
|---|
| 613 | | Proxy (A) | (peer)| Caching Proxy (B) |
|
|---|
| 614 | ----------------- ---------------------
|
|---|
| 615 | |
|
|---|
| 616 | |
|
|---|
| 617 | ----------
|
|---|
| 618 | | Client |
|
|---|
| 619 | ----------
|
|---|
| 620 |
|
|---|
| 621 | Client included for illustration purposes only
|
|---|
| 622 |
|
|---|
| 623 |
|
|---|
| 624 |
|
|---|
| 625 |
|
|---|
| 626 |
|
|---|
| 627 |
|
|---|
| 628 | Cooper, et al. Informational [Page 11]
|
|---|
| 629 | |
|---|
| 630 |
|
|---|
| 631 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 632 |
|
|---|
| 633 |
|
|---|
| 634 | An inbound request may be routed to one of a number of intermediate
|
|---|
| 635 | (caching) proxies based on a determination of whether that parent is
|
|---|
| 636 | better suited to resolving the request.
|
|---|
| 637 |
|
|---|
| 638 | For example, in the above figure, Cache Server C and Intermediate
|
|---|
| 639 | Caching Proxy B are peers of the Local Caching Proxy A, and may only
|
|---|
| 640 | be used when the resource requested by A already exists on either B
|
|---|
| 641 | or C. Intermediate Caching Proxies D & E are parents of A, and it is
|
|---|
| 642 | A's choice of which to use to resolve a particular request.
|
|---|
| 643 |
|
|---|
| 644 | The relationship between A & B only makes sense in a caching
|
|---|
| 645 | environment, while the relationships between A & D and A & E are also
|
|---|
| 646 | appropriate where D or E are non-caching proxies.
|
|---|
| 647 |
|
|---|
| 648 | Protocols used in these relationships can be found in Section 7.1.
|
|---|
| 649 |
|
|---|
| 650 | 3.2.3.2 (Caching) Proxy Arrays
|
|---|
| 651 |
|
|---|
| 652 | Where a user agent may have a relationship with a proxy, it is
|
|---|
| 653 | possible that it may instead have a relationship with an array of
|
|---|
| 654 | proxies arranged in a tightly coupled mesh.
|
|---|
| 655 |
|
|---|
| 656 | ----------------------
|
|---|
| 657 | ---------------------- |
|
|---|
| 658 | --------------------- | |
|
|---|
| 659 | | (Caching) Proxy | |-----
|
|---|
| 660 | | Array |----- ^ ^
|
|---|
| 661 | --------------------- ^ ^ | |
|
|---|
| 662 | ^ ^ | |--- |
|
|---|
| 663 | | |----- |
|
|---|
| 664 | --------------------------
|
|---|
| 665 |
|
|---|
| 666 | Protocols used in this relationship can be found in Section 7.2.
|
|---|
| 667 |
|
|---|
| 668 | 3.2.4 Network Element to Caching Proxy
|
|---|
| 669 |
|
|---|
| 670 | A network element performing traffic interception may choose to
|
|---|
| 671 | redirect requests from a client to a specific proxy within an array.
|
|---|
| 672 | (It may also choose not to redirect the traffic, in which case the
|
|---|
| 673 | relationship is between client and (replica) origin server, see
|
|---|
| 674 | Section 3.1.1.)
|
|---|
| 675 |
|
|---|
| 676 |
|
|---|
| 677 |
|
|---|
| 678 |
|
|---|
| 679 |
|
|---|
| 680 |
|
|---|
| 681 |
|
|---|
| 682 |
|
|---|
| 683 |
|
|---|
| 684 |
|
|---|
| 685 | Cooper, et al. Informational [Page 12]
|
|---|
| 686 | |
|---|
| 687 |
|
|---|
| 688 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 689 |
|
|---|
| 690 |
|
|---|
| 691 | ----------------- ----------------- -----------------
|
|---|
| 692 | | Caching Proxy | | Caching Proxy | | Caching Proxy |
|
|---|
| 693 | | Array | | Array | | Array |
|
|---|
| 694 | ----------------- ----------------- -----------------
|
|---|
| 695 | \ | /
|
|---|
| 696 | -----------------------------------------
|
|---|
| 697 | |
|
|---|
| 698 | --------------
|
|---|
| 699 | | Network |
|
|---|
| 700 | | Element |
|
|---|
| 701 | --------------
|
|---|
| 702 | |
|
|---|
| 703 | ///
|
|---|
| 704 | |
|
|---|
| 705 | ------------
|
|---|
| 706 | | Client |
|
|---|
| 707 | ------------
|
|---|
| 708 |
|
|---|
| 709 | The interception proxy may be directly in-line of the flow of traffic
|
|---|
| 710 | - in which case the intercepting network element and interception
|
|---|
| 711 | proxy form parts of the same hardware system - or may be out-of-path,
|
|---|
| 712 | requiring the intercepting network element to redirect traffic to
|
|---|
| 713 | another network segment. In this latter case, communication
|
|---|
| 714 | protocols enable the intercepting network element to stop and start
|
|---|
| 715 | redirecting traffic when the interception proxy becomes
|
|---|
| 716 | (un)available. Details of these protocols can be found in Section 8.
|
|---|
| 717 |
|
|---|
| 718 | 4. Replica Selection
|
|---|
| 719 |
|
|---|
| 720 | This section describes the schemes and protocols used in the
|
|---|
| 721 | cooperation and communication between client and replica origin web
|
|---|
| 722 | servers. The ideal situation is to discover an optimal replica
|
|---|
| 723 | origin server for clients to communicate with. Optimality is a
|
|---|
| 724 | policy based decision, often based upon proximity, but may be based
|
|---|
| 725 | on other criteria such as load.
|
|---|
| 726 |
|
|---|
| 727 | 4.1 Navigation Hyperlinks
|
|---|
| 728 |
|
|---|
| 729 | Best known reference:
|
|---|
| 730 | This memo.
|
|---|
| 731 |
|
|---|
| 732 | Description:
|
|---|
| 733 | The simplest of client to replica communication mechanisms. This
|
|---|
| 734 | utilizes hyperlink URIs embedded in web pages that point to the
|
|---|
| 735 | individual replica origin servers. The content consumer manually
|
|---|
| 736 | selects the link of the replica origin server they wish to use.
|
|---|
| 737 |
|
|---|
| 738 |
|
|---|
| 739 |
|
|---|
| 740 |
|
|---|
| 741 |
|
|---|
| 742 | Cooper, et al. Informational [Page 13]
|
|---|
| 743 | |
|---|
| 744 |
|
|---|
| 745 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 746 |
|
|---|
| 747 |
|
|---|
| 748 | Security:
|
|---|
| 749 | Relies on the protocol security associated with the appropriate
|
|---|
| 750 | URI scheme.
|
|---|
| 751 |
|
|---|
| 752 | Deployment:
|
|---|
| 753 | Probably the most commonly deployed client to replica
|
|---|
| 754 | communication mechanism. Ubiquitous interoperability with humans.
|
|---|
| 755 |
|
|---|
| 756 | Submitter:
|
|---|
| 757 | Document editors.
|
|---|
| 758 |
|
|---|
| 759 | 4.2 Replica HTTP Redirection
|
|---|
| 760 |
|
|---|
| 761 | Best known reference:
|
|---|
| 762 | This memo.
|
|---|
| 763 |
|
|---|
| 764 | Description:
|
|---|
| 765 | A simple and commonly used mechanism to connect clients with
|
|---|
| 766 | replica origin servers is to use HTTP redirection. Clients are
|
|---|
| 767 | redirected to an optimal replica origin server via the use of the
|
|---|
| 768 | HTTP [1] protocol response codes, e.g., 302 "Found", or 307
|
|---|
| 769 | "Temporary Redirect". A client establishes HTTP communication
|
|---|
| 770 | with one of the replica origin servers. The initially contacted
|
|---|
| 771 | replica origin server can then either choose to accept the service
|
|---|
| 772 | or redirect the client again. Refer to section 10.3 in HTTP/1.1
|
|---|
| 773 | [1] for information on HTTP response codes.
|
|---|
| 774 |
|
|---|
| 775 | Security:
|
|---|
| 776 | Relies entirely upon HTTP security.
|
|---|
| 777 |
|
|---|
| 778 | Deployment:
|
|---|
| 779 | Observed at a number of large web sites. Extent of usage in the
|
|---|
| 780 | Internet is unknown.
|
|---|
| 781 |
|
|---|
| 782 | Submitter:
|
|---|
| 783 | Document editors.
|
|---|
| 784 |
|
|---|
| 785 | 4.3 DNS Redirection
|
|---|
| 786 |
|
|---|
| 787 | Best known references:
|
|---|
| 788 |
|
|---|
| 789 | * RFC 1794 DNS Support for Load Balancing Proximity [8]
|
|---|
| 790 |
|
|---|
| 791 | * This memo
|
|---|
| 792 |
|
|---|
| 793 | Description:
|
|---|
| 794 | The Domain Name Service (DNS) provides a more sophisticated client
|
|---|
| 795 | to replica communication mechanism. This is accomplished by DNS
|
|---|
| 796 |
|
|---|
| 797 |
|
|---|
| 798 |
|
|---|
| 799 | Cooper, et al. Informational [Page 14]
|
|---|
| 800 | |
|---|
| 801 |
|
|---|
| 802 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 803 |
|
|---|
| 804 |
|
|---|
| 805 | servers that sort resolved IP addresses based upon quality of
|
|---|
| 806 | service policies. When a client resolves the name of an origin
|
|---|
| 807 | server, the enhanced DNS server sorts the available IP addresses
|
|---|
| 808 | of the replica origin servers starting with the most optimal
|
|---|
| 809 | replica and ending with the least optimal replica.
|
|---|
| 810 |
|
|---|
| 811 | Security:
|
|---|
| 812 | Relies entirely upon DNS security, and other protocols that may be
|
|---|
| 813 | used in determining the sort order.
|
|---|
| 814 |
|
|---|
| 815 | Deployment:
|
|---|
| 816 | Observed at a number of large web sites and large ISP web hosted
|
|---|
| 817 | services. Extent of usage in the Internet is unknown, but is
|
|---|
| 818 | believed to be increasing.
|
|---|
| 819 |
|
|---|
| 820 | Submitter:
|
|---|
| 821 | Document editors.
|
|---|
| 822 |
|
|---|
| 823 | 5. Inter-Replica Communication
|
|---|
| 824 |
|
|---|
| 825 | This section describes the cooperation and communication between
|
|---|
| 826 | master- and replica- origin servers. Used in replicating data sets
|
|---|
| 827 | between origin servers.
|
|---|
| 828 |
|
|---|
| 829 | 5.1 Batch Driven Replication
|
|---|
| 830 |
|
|---|
| 831 | Best known reference:
|
|---|
| 832 | This memo.
|
|---|
| 833 |
|
|---|
| 834 | Description:
|
|---|
| 835 | The replica origin server to be updated initiates communication
|
|---|
| 836 | with a master origin server. The communication is established at
|
|---|
| 837 | intervals based upon queued transactions which are scheduled for
|
|---|
| 838 | deferred processing. The scheduling mechanism policies vary, but
|
|---|
| 839 | generally are re-occurring at a specified time. Once
|
|---|
| 840 | communication is established, data sets are copied to the
|
|---|
| 841 | initiating replica origin server.
|
|---|
| 842 |
|
|---|
| 843 | Security:
|
|---|
| 844 | Relies upon the protocol being used to transfer the data set. FTP
|
|---|
| 845 | [4] and RDIST are the most common protocols observed.
|
|---|
| 846 |
|
|---|
| 847 | Deployment:
|
|---|
| 848 | Very common for synchronization of mirror sites in the Internet.
|
|---|
| 849 |
|
|---|
| 850 | Submitter:
|
|---|
| 851 | Document editors.
|
|---|
| 852 |
|
|---|
| 853 |
|
|---|
| 854 |
|
|---|
| 855 |
|
|---|
| 856 | Cooper, et al. Informational [Page 15]
|
|---|
| 857 | |
|---|
| 858 |
|
|---|
| 859 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 860 |
|
|---|
| 861 |
|
|---|
| 862 | 5.2 Demand Driven Replication
|
|---|
| 863 |
|
|---|
| 864 | Best known reference:
|
|---|
| 865 | This memo.
|
|---|
| 866 |
|
|---|
| 867 | Description:
|
|---|
| 868 | Replica origin servers acquire content as needed due to client
|
|---|
| 869 | demand. When a client requests a resource that is not in the data
|
|---|
| 870 | set of the replica origin server/surrogate, an attempt is made to
|
|---|
| 871 | resolve the request by acquiring the resource from the master
|
|---|
| 872 | origin server, returning it to the requesting client.
|
|---|
| 873 |
|
|---|
| 874 | Security:
|
|---|
| 875 | Relies upon the protocol being used to transfer the resources. FTP
|
|---|
| 876 | [4], Gopher [5], HTTP [1] and ICP [2] are the most common
|
|---|
| 877 | protocols observed.
|
|---|
| 878 |
|
|---|
| 879 | Deployment:
|
|---|
| 880 | Observed at several large web sites. Extent of usage in the
|
|---|
| 881 | Internet is unknown.
|
|---|
| 882 |
|
|---|
| 883 | Submitter:
|
|---|
| 884 | Document editors.
|
|---|
| 885 |
|
|---|
| 886 | 5.3 Synchronized Replication
|
|---|
| 887 |
|
|---|
| 888 | Best known reference:
|
|---|
| 889 | This memo.
|
|---|
| 890 |
|
|---|
| 891 | Description:
|
|---|
| 892 | Replicated origin servers cooperate using synchronized strategies
|
|---|
| 893 | and specialized replica protocols to keep the replica data sets
|
|---|
| 894 | coherent. Synchronization strategies range from tightly coherent
|
|---|
| 895 | (a few minutes) to loosely coherent (a few or more hours). Updates
|
|---|
| 896 | occur between replicas based upon the synchronization time
|
|---|
| 897 | constraints of the coherency model employed and are generally in
|
|---|
| 898 | the form of deltas only.
|
|---|
| 899 |
|
|---|
| 900 | Security:
|
|---|
| 901 | All of the known protocols utilize strong cryptographic key
|
|---|
| 902 | exchange methods, which are either based upon the Kerberos shared
|
|---|
| 903 | secret model or the public/private key RSA model.
|
|---|
| 904 |
|
|---|
| 905 | Deployment:
|
|---|
| 906 | Observed at a few sites, primarily at university campuses.
|
|---|
| 907 |
|
|---|
| 908 | Submitter:
|
|---|
| 909 | Document editors.
|
|---|
| 910 |
|
|---|
| 911 |
|
|---|
| 912 |
|
|---|
| 913 | Cooper, et al. Informational [Page 16]
|
|---|
| 914 | |
|---|
| 915 |
|
|---|
| 916 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 917 |
|
|---|
| 918 |
|
|---|
| 919 | Note:
|
|---|
| 920 | The editors are aware of at least two open source protocols - AFS
|
|---|
| 921 | and CODA - as well as the proprietary NRS protocol from Novell.
|
|---|
| 922 |
|
|---|
| 923 | 6. User Agent to Proxy Configuration
|
|---|
| 924 |
|
|---|
| 925 | This section describes the configuration, cooperation and
|
|---|
| 926 | communication between user agents and proxies.
|
|---|
| 927 |
|
|---|
| 928 | 6.1 Manual Proxy Configuration
|
|---|
| 929 |
|
|---|
| 930 | Best known reference:
|
|---|
| 931 | This memo.
|
|---|
| 932 |
|
|---|
| 933 | Description:
|
|---|
| 934 | Each user must configure her user agent by supplying information
|
|---|
| 935 | pertaining to proxied protocols and local policies.
|
|---|
| 936 |
|
|---|
| 937 | Security:
|
|---|
| 938 | The potential for doing wrong is high; each user individually sets
|
|---|
| 939 | preferences.
|
|---|
| 940 |
|
|---|
| 941 | Deployment:
|
|---|
| 942 | Widely deployed, used in all current browsers. Most browsers also
|
|---|
| 943 | support additional options.
|
|---|
| 944 |
|
|---|
| 945 | Submitter:
|
|---|
| 946 | Document editors.
|
|---|
| 947 |
|
|---|
| 948 | 6.2 Proxy Auto Configuration (PAC)
|
|---|
| 949 |
|
|---|
| 950 | Best known reference:
|
|---|
| 951 | "Navigator Proxy Auto-Config File Format" [12]
|
|---|
| 952 |
|
|---|
| 953 | Description:
|
|---|
| 954 | A JavaScript script retrieved from a web server is executed for
|
|---|
| 955 | each URL accessed to determine the appropriate proxy (if any) to
|
|---|
| 956 | be used to access the resource. User agents must be configured to
|
|---|
| 957 | request this script upon startup. There is no bootstrap
|
|---|
| 958 | mechanism, manual configuration is necessary.
|
|---|
| 959 |
|
|---|
| 960 | Despite manual configuration, the process of proxy configuration
|
|---|
| 961 | is simplified by centralizing it within a script at a single
|
|---|
| 962 | location.
|
|---|
| 963 |
|
|---|
| 964 | Security:
|
|---|
| 965 | Common policy per organization possible but still requires initial
|
|---|
| 966 | manual configuration. PAC is better than "manual proxy
|
|---|
| 967 |
|
|---|
| 968 |
|
|---|
| 969 |
|
|---|
| 970 | Cooper, et al. Informational [Page 17]
|
|---|
| 971 | |
|---|
| 972 |
|
|---|
| 973 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 974 |
|
|---|
| 975 |
|
|---|
| 976 | configuration" since PAC administrators may update the proxy
|
|---|
| 977 | configuration without further user intervention.
|
|---|
| 978 |
|
|---|
| 979 | Interoperability of PAC files is not high, since different
|
|---|
| 980 | browsers have slightly different interpretations of the same
|
|---|
| 981 | script, possibly leading to undesired effects.
|
|---|
| 982 |
|
|---|
| 983 | Deployment:
|
|---|
| 984 | Implemented in Netscape Navigator and Microsoft Internet Explorer.
|
|---|
| 985 |
|
|---|
| 986 | Submitter:
|
|---|
| 987 | Document editors.
|
|---|
| 988 |
|
|---|
| 989 | 6.3 Cache Array Routing Protocol (CARP) v1.0
|
|---|
| 990 |
|
|---|
| 991 | Best known references:
|
|---|
| 992 |
|
|---|
| 993 | * "Cache Array Routing Protocol" [14] (work in progress)
|
|---|
| 994 |
|
|---|
| 995 | * "Cache Array Routing Protocol (CARP) v1.0 Specifications" [15]
|
|---|
| 996 |
|
|---|
| 997 | * "Cache Array Routing Protocol and Microsoft Proxy Server 2.0"
|
|---|
| 998 | [16]
|
|---|
| 999 |
|
|---|
| 1000 | Description:
|
|---|
| 1001 | User agents may use CARP directly as a hash function based proxy
|
|---|
| 1002 | selection mechanism. They need to be configured with the location
|
|---|
| 1003 | of the cluster information.
|
|---|
| 1004 |
|
|---|
| 1005 | Security:
|
|---|
| 1006 | Security considerations are not covered in the specification works
|
|---|
| 1007 | in progress.
|
|---|
| 1008 |
|
|---|
| 1009 | Deployment:
|
|---|
| 1010 | Implemented in Microsoft Proxy Server, Squid. Implemented in user
|
|---|
| 1011 | agents via PAC scripts.
|
|---|
| 1012 |
|
|---|
| 1013 | Submitter:
|
|---|
| 1014 | Document editors.
|
|---|
| 1015 |
|
|---|
| 1016 | 6.4 Web Proxy Auto-Discovery Protocol (WPAD)
|
|---|
| 1017 |
|
|---|
| 1018 | Best known reference:
|
|---|
| 1019 | "The Web Proxy Auto-Discovery Protocol" [13] (work in progress)
|
|---|
| 1020 |
|
|---|
| 1021 | Description:
|
|---|
| 1022 | WPAD uses a collection of pre-existing Internet resource discovery
|
|---|
| 1023 | mechanisms to perform web proxy auto-discovery.
|
|---|
| 1024 |
|
|---|
| 1025 |
|
|---|
| 1026 |
|
|---|
| 1027 | Cooper, et al. Informational [Page 18]
|
|---|
| 1028 | |
|---|
| 1029 |
|
|---|
| 1030 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1031 |
|
|---|
| 1032 |
|
|---|
| 1033 | The only goal of WPAD is to locate the PAC URL [12]. WPAD does
|
|---|
| 1034 | not specify which proxies will be used. WPAD supplies the PAC
|
|---|
| 1035 | URL, and the PAC script then operates as defined above to choose
|
|---|
| 1036 | proxies per resource request.
|
|---|
| 1037 |
|
|---|
| 1038 | The WPAD protocol specifies the following:
|
|---|
| 1039 |
|
|---|
| 1040 | * how to use each mechanism for the specific purpose of web proxy
|
|---|
| 1041 | auto-discovery
|
|---|
| 1042 |
|
|---|
| 1043 | * the order in which the mechanisms should be performed
|
|---|
| 1044 |
|
|---|
| 1045 | * the minimal set of mechanisms which must be attempted by a WPAD
|
|---|
| 1046 | compliant user agent
|
|---|
| 1047 |
|
|---|
| 1048 | The resource discovery mechanisms utilized by WPAD are as follows:
|
|---|
| 1049 |
|
|---|
| 1050 | * Dynamic Host Configuration Protocol DHCP
|
|---|
| 1051 |
|
|---|
| 1052 | * Service Location Protocol SLP
|
|---|
| 1053 |
|
|---|
| 1054 | * "Well Known Aliases" using DNS A records
|
|---|
| 1055 |
|
|---|
| 1056 | * DNS SRV records
|
|---|
| 1057 |
|
|---|
| 1058 | * "service: URLs" in DNS TXT records
|
|---|
| 1059 |
|
|---|
| 1060 | Security:
|
|---|
| 1061 | Relies upon DNS and HTTP security.
|
|---|
| 1062 |
|
|---|
| 1063 | Deployment:
|
|---|
| 1064 | Implemented in some user agents and caching proxy servers. More
|
|---|
| 1065 | than two independent implementations.
|
|---|
| 1066 |
|
|---|
| 1067 | Submitter:
|
|---|
| 1068 | Josh Cohen
|
|---|
| 1069 |
|
|---|
| 1070 | 7. Inter-Proxy Communication
|
|---|
| 1071 |
|
|---|
| 1072 | 7.1 Loosely coupled Inter-Proxy Communication
|
|---|
| 1073 |
|
|---|
| 1074 | This section describes the cooperation and communication between
|
|---|
| 1075 | caching proxies.
|
|---|
| 1076 |
|
|---|
| 1077 | 7.1.1 Internet Cache Protocol (ICP)
|
|---|
| 1078 |
|
|---|
| 1079 | Best known reference:
|
|---|
| 1080 | RFC 2186 Internet Cache Protocol (ICP), version 2 [2]
|
|---|
| 1081 |
|
|---|
| 1082 |
|
|---|
| 1083 |
|
|---|
| 1084 | Cooper, et al. Informational [Page 19]
|
|---|
| 1085 | |
|---|
| 1086 |
|
|---|
| 1087 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1088 |
|
|---|
| 1089 |
|
|---|
| 1090 | Description:
|
|---|
| 1091 | ICP is used by proxies to query other (caching) proxies about web
|
|---|
| 1092 | resources, to see if the requested resource is present on the
|
|---|
| 1093 | other system.
|
|---|
| 1094 |
|
|---|
| 1095 | ICP uses UDP. Since UDP is an uncorrected network transport
|
|---|
| 1096 | protocol, an estimate of network congestion and availability may
|
|---|
| 1097 | be calculated by ICP loss. This rudimentary loss measurement
|
|---|
| 1098 | provides, together with round trip times, a load balancing method
|
|---|
| 1099 | for caches.
|
|---|
| 1100 |
|
|---|
| 1101 | Security:
|
|---|
| 1102 | See RFC 2187 [3]
|
|---|
| 1103 |
|
|---|
| 1104 | ICP does not convey information about HTTP headers associated with
|
|---|
| 1105 | resources. HTTP headers may include access control and cache
|
|---|
| 1106 | directives. Since proxies ask for the availability of resources,
|
|---|
| 1107 | and subsequently retrieve them using HTTP, false cache hits may
|
|---|
| 1108 | occur (object present in cache, but not accessible to a sibling is
|
|---|
| 1109 | one example).
|
|---|
| 1110 |
|
|---|
| 1111 | ICP suffers from all the security problems of UDP.
|
|---|
| 1112 |
|
|---|
| 1113 | Deployment:
|
|---|
| 1114 | Widely deployed. Most current caching proxy implementations
|
|---|
| 1115 | support ICP in some form.
|
|---|
| 1116 |
|
|---|
| 1117 | Submitter:
|
|---|
| 1118 | Document editors.
|
|---|
| 1119 |
|
|---|
| 1120 | See also:
|
|---|
| 1121 | "Internet Cache Protocol Extension" [17] (work in progress)
|
|---|
| 1122 |
|
|---|
| 1123 | 7.1.2 Hyper Text Caching Protocol
|
|---|
| 1124 |
|
|---|
| 1125 | Best known reference:
|
|---|
| 1126 | RFC 2756 Hyper Text Caching Protocol (HTCP/0.0) [9]
|
|---|
| 1127 |
|
|---|
| 1128 | Description:
|
|---|
| 1129 | HTCP is a protocol for discovering HTTP caching proxies and cached
|
|---|
| 1130 | data, managing sets of HTTP caching proxies, and monitoring cache
|
|---|
| 1131 | activity.
|
|---|
| 1132 |
|
|---|
| 1133 | HTCP requests include HTTP header material, while ICPv2 does not,
|
|---|
| 1134 | enabling HTCP replies to more accurately describe the behaviour
|
|---|
| 1135 | that would occur as a result of a subsequent HTTP request for the
|
|---|
| 1136 | same resource.
|
|---|
| 1137 |
|
|---|
| 1138 |
|
|---|
| 1139 |
|
|---|
| 1140 |
|
|---|
| 1141 | Cooper, et al. Informational [Page 20]
|
|---|
| 1142 | |
|---|
| 1143 |
|
|---|
| 1144 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1145 |
|
|---|
| 1146 |
|
|---|
| 1147 | Security:
|
|---|
| 1148 | Optionally uses HMAC-MD5 [11] shared secret authentication.
|
|---|
| 1149 | Protocol is subject to attack if authentication is not used.
|
|---|
| 1150 |
|
|---|
| 1151 | Deployment:
|
|---|
| 1152 | HTCP is implemented in Squid and the "Web Gateway Interceptor".
|
|---|
| 1153 |
|
|---|
| 1154 | Submitter:
|
|---|
| 1155 | Document editors.
|
|---|
| 1156 |
|
|---|
| 1157 | 7.1.3 Cache Digest
|
|---|
| 1158 |
|
|---|
| 1159 | Best known references:
|
|---|
| 1160 |
|
|---|
| 1161 | * "Cache Digest Specification - version 5" [21]
|
|---|
| 1162 |
|
|---|
| 1163 | * "Summary Cache: A Scalable Wide-Area Web Cache Sharing
|
|---|
| 1164 | Protocol" [10] (see note)
|
|---|
| 1165 |
|
|---|
| 1166 | Description:
|
|---|
| 1167 | Cache Digests are a response to the problems of latency and
|
|---|
| 1168 | congestion associated with previous inter-cache communication
|
|---|
| 1169 | mechanisms such as the Internet Cache Protocol (ICP) [2] and the
|
|---|
| 1170 | Hyper Text Cache Protocol [9]. Unlike these protocols, Cache
|
|---|
| 1171 | Digests support peering between caching proxies and cache servers
|
|---|
| 1172 | without a request-response exchange taking place for each inbound
|
|---|
| 1173 | request. Instead, a summary of the contents in cache (the Digest)
|
|---|
| 1174 | is fetched by other systems that peer with it. Using Cache
|
|---|
| 1175 | Digests it is possible to determine with a relatively high degree
|
|---|
| 1176 | of accuracy whether a given resource is cached by a particular
|
|---|
| 1177 | system.
|
|---|
| 1178 |
|
|---|
| 1179 | Cache Digests are both an exchange protocol and a data format.
|
|---|
| 1180 |
|
|---|
| 1181 | Security:
|
|---|
| 1182 | If the contents of a Digest are sensitive, they should be
|
|---|
| 1183 | protected. Any methods which would normally be applied to secure
|
|---|
| 1184 | an HTTP connection can be applied to Cache Digests.
|
|---|
| 1185 |
|
|---|
| 1186 | A 'Trojan horse' attack is currently possible in a mesh: System A
|
|---|
| 1187 | A can build a fake peer Digest for system B and serve it to B's
|
|---|
| 1188 | peers if requested. This way A can direct traffic toward/from B.
|
|---|
| 1189 | The impact of this problem is minimized by the 'pull' model of
|
|---|
| 1190 | transferring Cache Digests from one system to another.
|
|---|
| 1191 |
|
|---|
| 1192 |
|
|---|
| 1193 |
|
|---|
| 1194 |
|
|---|
| 1195 |
|
|---|
| 1196 |
|
|---|
| 1197 |
|
|---|
| 1198 | Cooper, et al. Informational [Page 21]
|
|---|
| 1199 | |
|---|
| 1200 |
|
|---|
| 1201 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1202 |
|
|---|
| 1203 |
|
|---|
| 1204 | Cache Digests provide knowledge about peer cache content on a URL
|
|---|
| 1205 | level. Hence, they do not dictate a particular level of policy
|
|---|
| 1206 | management and can be used to implement various policies on any
|
|---|
| 1207 | level (user, organization, etc.).
|
|---|
| 1208 |
|
|---|
| 1209 | Deployment:
|
|---|
| 1210 | Cache Digests are supported in Squid.
|
|---|
| 1211 |
|
|---|
| 1212 | Cache Meshes: NLANR Mesh; TF-CACHE Mesh (European Academic
|
|---|
| 1213 | networks
|
|---|
| 1214 |
|
|---|
| 1215 | Submitter:
|
|---|
| 1216 | Alex Rousskov for [21], Pei Cao for [10].
|
|---|
| 1217 |
|
|---|
| 1218 | Note: The technology of Summary Cache [10] is patent pending by the
|
|---|
| 1219 | University of Wisconsin-Madison.
|
|---|
| 1220 |
|
|---|
| 1221 | 7.1.4 Cache Pre-filling
|
|---|
| 1222 |
|
|---|
| 1223 | Best known reference:
|
|---|
| 1224 | "Pre-filling a cache - A satellite overview" [20] (work in
|
|---|
| 1225 | progress)
|
|---|
| 1226 |
|
|---|
| 1227 | Description:
|
|---|
| 1228 | Cache pre-filling is a push-caching implementation. It is
|
|---|
| 1229 | particularly well adapted to IP-multicast networks because it
|
|---|
| 1230 | allows preselected resources to be simultaneously inserted into
|
|---|
| 1231 | caches within the targeted multicast group. Different
|
|---|
| 1232 | implementations of cache pre-filling already exist, especially in
|
|---|
| 1233 | satellite contexts. However, there is still no standard for this
|
|---|
| 1234 | kind of push-caching and vendors propose solutions either based on
|
|---|
| 1235 | dedicated equipment or public domain caches extended with a pre-
|
|---|
| 1236 | filling module.
|
|---|
| 1237 |
|
|---|
| 1238 | Security:
|
|---|
| 1239 | Relies on the inter-cache protocols being employed.
|
|---|
| 1240 |
|
|---|
| 1241 | Deployment:
|
|---|
| 1242 | Observed in two commercial content distribution service providers.
|
|---|
| 1243 |
|
|---|
| 1244 | Submitter:
|
|---|
| 1245 | Ivan Lovric
|
|---|
| 1246 |
|
|---|
| 1247 | 7.2 Tightly Coupled Inter-Cache Communication
|
|---|
| 1248 |
|
|---|
| 1249 | 7.2.1 Cache Array Routing Protocol (CARP) v1.0
|
|---|
| 1250 |
|
|---|
| 1251 | Also see Section 6.3
|
|---|
| 1252 |
|
|---|
| 1253 |
|
|---|
| 1254 |
|
|---|
| 1255 | Cooper, et al. Informational [Page 22]
|
|---|
| 1256 | |
|---|
| 1257 |
|
|---|
| 1258 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1259 |
|
|---|
| 1260 |
|
|---|
| 1261 | Best known references:
|
|---|
| 1262 |
|
|---|
| 1263 | * "Cache Array Routing Protocol" [14] (work in progress)
|
|---|
| 1264 |
|
|---|
| 1265 | * "Cache Array Routing Protocol (CARP) v1.0 Specifications" [15]
|
|---|
| 1266 |
|
|---|
| 1267 | * "Cache Array Routing Protocol and Microsoft Proxy Server 2.0"
|
|---|
| 1268 | [16]
|
|---|
| 1269 |
|
|---|
| 1270 | Description:
|
|---|
| 1271 | CARP is a hashing function for dividing URL-space among a cluster
|
|---|
| 1272 | of proxies. Included in CARP is the definition of a Proxy Array
|
|---|
| 1273 | Membership Table, and ways to download this information.
|
|---|
| 1274 |
|
|---|
| 1275 | A user agent which implements CARP v1.0 can allocate and
|
|---|
| 1276 | intelligently route requests for the URLs to any member of the
|
|---|
| 1277 | Proxy Array. Due to the resulting sorting of requests through
|
|---|
| 1278 | these proxies, duplication of cache contents is eliminated and
|
|---|
| 1279 | global cache hit rates may be improved.
|
|---|
| 1280 |
|
|---|
| 1281 | Security:
|
|---|
| 1282 | Security considerations are not covered in the specification works
|
|---|
| 1283 | in progress.
|
|---|
| 1284 |
|
|---|
| 1285 | Deployment:
|
|---|
| 1286 | Implemented in caching proxy servers. More than two independent
|
|---|
| 1287 | implementations.
|
|---|
| 1288 |
|
|---|
| 1289 | Submitter:
|
|---|
| 1290 | Document editors.
|
|---|
| 1291 |
|
|---|
| 1292 | 8. Network Element Communication
|
|---|
| 1293 |
|
|---|
| 1294 | This section describes the cooperation and communication between
|
|---|
| 1295 | proxies and network elements. Examples of such network elements
|
|---|
| 1296 | include routers and switches. Generally used for deploying
|
|---|
| 1297 | interception proxies and/or diffused arrays.
|
|---|
| 1298 |
|
|---|
| 1299 | 8.1 Web Cache Control Protocol (WCCP)
|
|---|
| 1300 |
|
|---|
| 1301 | Best known references:
|
|---|
| 1302 | "Web Cache Control Protocol" [18][19] (work in progress)
|
|---|
| 1303 |
|
|---|
| 1304 | Note: The name used for this protocol varies, sometimes referred
|
|---|
| 1305 | to as the "Web Cache Coordination Protocol", but frequently just
|
|---|
| 1306 | "WCCP" to avoid confusion
|
|---|
| 1307 |
|
|---|
| 1308 |
|
|---|
| 1309 |
|
|---|
| 1310 |
|
|---|
| 1311 |
|
|---|
| 1312 | Cooper, et al. Informational [Page 23]
|
|---|
| 1313 | |
|---|
| 1314 |
|
|---|
| 1315 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1316 |
|
|---|
| 1317 |
|
|---|
| 1318 | Description:
|
|---|
| 1319 | WCCP V1 runs between a router functioning as a redirecting network
|
|---|
| 1320 | element and out-of-path interception proxies. The protocol allows
|
|---|
| 1321 | one or more proxies to register with a single router to receive
|
|---|
| 1322 | redirected traffic. It also allows one of the proxies, the
|
|---|
| 1323 | designated proxy, to dictate to the router how redirected traffic
|
|---|
| 1324 | is distributed across the array.
|
|---|
| 1325 |
|
|---|
| 1326 | WCCP V2 additionally runs between multiple routers and the
|
|---|
| 1327 | proxies.
|
|---|
| 1328 |
|
|---|
| 1329 | Security:
|
|---|
| 1330 | WCCP V1 has no security features.
|
|---|
| 1331 | WCCP V2 provides optional authentication of protocol packets.
|
|---|
| 1332 |
|
|---|
| 1333 | Deployment:
|
|---|
| 1334 | Network elements: WCCP is deployed on a wide range of Cisco
|
|---|
| 1335 | routers.
|
|---|
| 1336 | Caching proxies: WCCP is deployed on a number of vendors' caching
|
|---|
| 1337 | proxies.
|
|---|
| 1338 |
|
|---|
| 1339 | Submitter:
|
|---|
| 1340 | David Forster
|
|---|
| 1341 | Document editors.
|
|---|
| 1342 |
|
|---|
| 1343 | 8.2 Network Element Control Protocol (NECP)
|
|---|
| 1344 |
|
|---|
| 1345 | Best known reference:
|
|---|
| 1346 | "NECP: The Network Element Control Protocol" [22] (work in
|
|---|
| 1347 | progress)
|
|---|
| 1348 |
|
|---|
| 1349 | Description:
|
|---|
| 1350 | NECP provides methods for network elements to learn about server
|
|---|
| 1351 | capabilities, availability, and hints as to which flows can and
|
|---|
| 1352 | cannot be serviced. This allows network elements to perform load
|
|---|
| 1353 | balancing across a farm of servers, redirection to interception
|
|---|
| 1354 | proxies, and cut-through of flows that cannot be served by the
|
|---|
| 1355 | farm.
|
|---|
| 1356 |
|
|---|
| 1357 | Security:
|
|---|
| 1358 | Optionally uses HMAC-SHA-1 [11] shared secret authentication along
|
|---|
| 1359 | with complex sequence numbers to provide moderately strong
|
|---|
| 1360 | security. Protocol is subject to attack if authentication is not
|
|---|
| 1361 | used.
|
|---|
| 1362 |
|
|---|
| 1363 | Deployment:
|
|---|
| 1364 | Unknown at present; several network element and caching proxy
|
|---|
| 1365 | vendors have expressed intent to implement the protocol.
|
|---|
| 1366 |
|
|---|
| 1367 |
|
|---|
| 1368 |
|
|---|
| 1369 | Cooper, et al. Informational [Page 24]
|
|---|
| 1370 | |
|---|
| 1371 |
|
|---|
| 1372 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1373 |
|
|---|
| 1374 |
|
|---|
| 1375 | Submitter:
|
|---|
| 1376 | Gary Tomlinson
|
|---|
| 1377 |
|
|---|
| 1378 | 8.3 SOCKS
|
|---|
| 1379 |
|
|---|
| 1380 | Best known reference:
|
|---|
| 1381 | RFC 1928 SOCKS Protocol Version 5 [7]
|
|---|
| 1382 |
|
|---|
| 1383 | Description:
|
|---|
| 1384 | SOCKS is primarily used as a caching proxy to firewall protocol.
|
|---|
| 1385 | Although firewalls don't conform to the narrowly defined network
|
|---|
| 1386 | element definition above, they are a integral part of the network
|
|---|
| 1387 | infrastructure. When used in conjunction with a firewall, SOCKS
|
|---|
| 1388 | provides a authenticated tunnel between the caching proxy and the
|
|---|
| 1389 | firewall.
|
|---|
| 1390 |
|
|---|
| 1391 | Security:
|
|---|
| 1392 | An extensive framework provides for multiple authentication
|
|---|
| 1393 | methods. Currently, SSL, CHAP, DES, 3DES are known to be
|
|---|
| 1394 | available.
|
|---|
| 1395 |
|
|---|
| 1396 | Deployment:
|
|---|
| 1397 | SOCKS is widely deployed in the Internet.
|
|---|
| 1398 |
|
|---|
| 1399 | Submitter:
|
|---|
| 1400 | Document editors.
|
|---|
| 1401 |
|
|---|
| 1402 | 9. Security Considerations
|
|---|
| 1403 |
|
|---|
| 1404 | This document provides a taxonomy for web caching and replication.
|
|---|
| 1405 | Recommended practice, architecture and protocols are not described in
|
|---|
| 1406 | detail.
|
|---|
| 1407 |
|
|---|
| 1408 | By definition, replication and caching involve the copying of
|
|---|
| 1409 | resources. There are legal implications of making and keeping
|
|---|
| 1410 | transient or permanent copies; these are not covered here.
|
|---|
| 1411 |
|
|---|
| 1412 | Information on security of each protocol referred to by this memo is
|
|---|
| 1413 | provided in the preceding sections, and in their accompanying
|
|---|
| 1414 | documentation. HTTP security is discussed in section 15 of RFC 2616
|
|---|
| 1415 | [1], the HTTP/1.1 specification, and to a lesser extent in RFC 1945
|
|---|
| 1416 | [6], the HTTP/1.0 specification. RFC 2616 contains security
|
|---|
| 1417 | considerations for HTTP proxies.
|
|---|
| 1418 |
|
|---|
| 1419 |
|
|---|
| 1420 |
|
|---|
| 1421 |
|
|---|
| 1422 |
|
|---|
| 1423 |
|
|---|
| 1424 |
|
|---|
| 1425 |
|
|---|
| 1426 | Cooper, et al. Informational [Page 25]
|
|---|
| 1427 | |
|---|
| 1428 |
|
|---|
| 1429 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1430 |
|
|---|
| 1431 |
|
|---|
| 1432 | Caching proxies have the same security issues as other application
|
|---|
| 1433 | level proxies. Application level proxies are not covered in these
|
|---|
| 1434 | security considerations. IP number based authentication is
|
|---|
| 1435 | problematic when a proxy is involved in the communications. Details
|
|---|
| 1436 | are not discussed here.
|
|---|
| 1437 |
|
|---|
| 1438 | 9.1 Authentication
|
|---|
| 1439 |
|
|---|
| 1440 | Requests for web resources, and responses to such requests, may be
|
|---|
| 1441 | directed to replicas and/or may flow through intermediate proxies.
|
|---|
| 1442 | The integrity of communication needs to be preserved to ensure
|
|---|
| 1443 | protection from both loss of access and from unintended change.
|
|---|
| 1444 |
|
|---|
| 1445 | 9.1.1 Man in the middle attacks
|
|---|
| 1446 |
|
|---|
| 1447 | HTTP proxies are men-in-the-middle, the perfect place for a man-in-
|
|---|
| 1448 | the-middle-attack. A discussion of this is found in section 15 of
|
|---|
| 1449 | RFC 2616 [1].
|
|---|
| 1450 |
|
|---|
| 1451 | 9.1.2 Trusted third party
|
|---|
| 1452 |
|
|---|
| 1453 | A proxy must either be trusted to act on behalf of the origin server
|
|---|
| 1454 | and/or client, or it must act as a tunnel. When presenting cached
|
|---|
| 1455 | objects to clients, the clients need to trust the caching proxy to
|
|---|
| 1456 | act on behalf on the origin server.
|
|---|
| 1457 |
|
|---|
| 1458 | A replica may get accreditation from the origin server.
|
|---|
| 1459 |
|
|---|
| 1460 | 9.1.3 Authentication based on IP number
|
|---|
| 1461 |
|
|---|
| 1462 | Authentication based on the client's IP number is problematic when
|
|---|
| 1463 | connecting through a proxy, since the authenticating device only has
|
|---|
| 1464 | access to the proxy's IP number. One (problematic) solution to this
|
|---|
| 1465 | is for the proxy to spoof the client's IP number for inbound
|
|---|
| 1466 | requests.
|
|---|
| 1467 |
|
|---|
| 1468 | Authentication based on IP number assumes that the end-to-end
|
|---|
| 1469 | properties of the Internet are preserved. This is typically not the
|
|---|
| 1470 | case for environments containing interception proxies.
|
|---|
| 1471 |
|
|---|
| 1472 | 9.2 Privacy
|
|---|
| 1473 |
|
|---|
| 1474 | 9.2.1 Trusted third party
|
|---|
| 1475 |
|
|---|
| 1476 | When using a replication service, one must trust both the replica
|
|---|
| 1477 | origin server and the replica selection system.
|
|---|
| 1478 |
|
|---|
| 1479 |
|
|---|
| 1480 |
|
|---|
| 1481 |
|
|---|
| 1482 |
|
|---|
| 1483 | Cooper, et al. Informational [Page 26]
|
|---|
| 1484 | |
|---|
| 1485 |
|
|---|
| 1486 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1487 |
|
|---|
| 1488 |
|
|---|
| 1489 | Redirection of traffic - either by automated replica selection
|
|---|
| 1490 | methods, or within proxies - may introduce third parties the end user
|
|---|
| 1491 | and/or origin server must to trust. In the case of interception
|
|---|
| 1492 | proxies, such third parties are often unknown to both end points of
|
|---|
| 1493 | the communication. Unknown third parties may have security
|
|---|
| 1494 | implications.
|
|---|
| 1495 |
|
|---|
| 1496 | Both proxies and replica selection services may have access to
|
|---|
| 1497 | aggregated access information. A proxy typically knows about
|
|---|
| 1498 | accesses by each client using it, information that is more sensitive
|
|---|
| 1499 | than the information held by a single origin server.
|
|---|
| 1500 |
|
|---|
| 1501 | 9.2.2 Logs and legal implications
|
|---|
| 1502 |
|
|---|
| 1503 | Logs from proxies should be kept secure, since they provide
|
|---|
| 1504 | information about users and their patterns of behaviour. A proxy's
|
|---|
| 1505 | log is even more sensitive than a web server log, as every request
|
|---|
| 1506 | from the user population goes through the proxy. Logs from replica
|
|---|
| 1507 | origin servers may need to be amalgamated to get aggregated
|
|---|
| 1508 | statistics from a service, and transporting logs across borders may
|
|---|
| 1509 | have legal implications. Log handling is restricted by law in some
|
|---|
| 1510 | countries.
|
|---|
| 1511 |
|
|---|
| 1512 | Requirements for object security and privacy are the same in a web
|
|---|
| 1513 | replication and caching system as it is in the Internet at large. The
|
|---|
| 1514 | only reliable solution is strong cryptography. End-to-end encryption
|
|---|
| 1515 | frequently makes resources uncacheable, as in the case of SSL
|
|---|
| 1516 | encrypted web sessions.
|
|---|
| 1517 |
|
|---|
| 1518 | 9.3 Service security
|
|---|
| 1519 |
|
|---|
| 1520 | 9.3.1 Denial of service
|
|---|
| 1521 |
|
|---|
| 1522 | Any redirection of traffic is susceptible to denial of service
|
|---|
| 1523 | attacks at the redirect point, and both proxies and replica selection
|
|---|
| 1524 | services may redirect traffic.
|
|---|
| 1525 |
|
|---|
| 1526 | By attacking a proxy, access to all servers may be denied for a large
|
|---|
| 1527 | set of clients.
|
|---|
| 1528 |
|
|---|
| 1529 | It has been argued that introduction of an interception proxy is a
|
|---|
| 1530 | denial of service attack, since the end-to-end nature of the Internet
|
|---|
| 1531 | is destroyed without the content consumer's knowledge.
|
|---|
| 1532 |
|
|---|
| 1533 | 9.3.2 Replay attack
|
|---|
| 1534 |
|
|---|
| 1535 | A caching proxy is by definition a replay attack.
|
|---|
| 1536 |
|
|---|
| 1537 |
|
|---|
| 1538 |
|
|---|
| 1539 |
|
|---|
| 1540 | Cooper, et al. Informational [Page 27]
|
|---|
| 1541 | |
|---|
| 1542 |
|
|---|
| 1543 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1544 |
|
|---|
| 1545 |
|
|---|
| 1546 | 9.3.3 Stupid configuration of proxies
|
|---|
| 1547 |
|
|---|
| 1548 | It is quite easy to have a stupid configuration which will harm
|
|---|
| 1549 | service for content consumers. This is the most common security
|
|---|
| 1550 | problem with proxies.
|
|---|
| 1551 |
|
|---|
| 1552 | 9.3.4 Copyrighted transient copies
|
|---|
| 1553 |
|
|---|
| 1554 | The legislative forces of the world are considering the question of
|
|---|
| 1555 | transient copies, like those kept in replication and caching system,
|
|---|
| 1556 | being legal. The legal implications of replication and caching are
|
|---|
| 1557 | subject to local law.
|
|---|
| 1558 |
|
|---|
| 1559 | Caching proxies need to preserve the protocol output, including
|
|---|
| 1560 | headers. Replication services need to preserve the source of the
|
|---|
| 1561 | objects.
|
|---|
| 1562 |
|
|---|
| 1563 | 9.3.5 Application level access
|
|---|
| 1564 |
|
|---|
| 1565 | Caching proxies are application level components in the traffic flow
|
|---|
| 1566 | path, and may give intruders access to information that was
|
|---|
| 1567 | previously only available at the network level in a proxy-free world.
|
|---|
| 1568 | Some network level equipment may have required physical access to get
|
|---|
| 1569 | sensitive information. Introduction of application level components
|
|---|
| 1570 | may require additional system security.
|
|---|
| 1571 |
|
|---|
| 1572 | 10. Acknowledgements
|
|---|
| 1573 |
|
|---|
| 1574 | The editors would like to thank the following for their assistance:
|
|---|
| 1575 | David Forster, Alex Rousskov, Josh Cohen, John Martin, John Dilley,
|
|---|
| 1576 | Ivan Lovric, Joe Touch, Henrik Nordstrom, Patrick McManus, Duane
|
|---|
| 1577 | Wessels, Wojtek Sylwestrzak, Ted Hardie, Misha Rabinovich, Larry
|
|---|
| 1578 | Masinter, Keith Moore, Roy Fielding, Patrik Faltstrom, Hilarie Orman,
|
|---|
| 1579 | Mark Nottingham and Oskar Batuner.
|
|---|
| 1580 |
|
|---|
| 1581 | References
|
|---|
| 1582 |
|
|---|
| 1583 | [1] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
|
|---|
| 1584 | Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
|
|---|
| 1585 | HTTP/1.1", RFC 2616, June 1999.
|
|---|
| 1586 |
|
|---|
| 1587 | [2] Wessels, D. and K. Claffy, "Internet Cache Protocol (ICP),
|
|---|
| 1588 | Version 2", RFC 2186, September 1997.
|
|---|
| 1589 |
|
|---|
| 1590 | [3] Wessels, D. and K. Claffy, "Application of Internet Cache
|
|---|
| 1591 | Protocol (ICP), Version 2", RFC 2187, September 1997.
|
|---|
| 1592 |
|
|---|
| 1593 |
|
|---|
| 1594 |
|
|---|
| 1595 |
|
|---|
| 1596 |
|
|---|
| 1597 | Cooper, et al. Informational [Page 28]
|
|---|
| 1598 | |
|---|
| 1599 |
|
|---|
| 1600 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1601 |
|
|---|
| 1602 |
|
|---|
| 1603 | [4] Postel, J. and J. Reynolds, "File Transfer Protocol (FTP)", STD
|
|---|
| 1604 | 9, RFC 959, October 1985.
|
|---|
| 1605 |
|
|---|
| 1606 | [5] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D., Torrey,
|
|---|
| 1607 | D. and B. Alberti, "The Internet Gopher Protocol", RFC 1436,
|
|---|
| 1608 | March 1993.
|
|---|
| 1609 |
|
|---|
| 1610 | [6] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext
|
|---|
| 1611 | Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
|
|---|
| 1612 |
|
|---|
| 1613 | [7] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D. and L.
|
|---|
| 1614 | Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996.
|
|---|
| 1615 |
|
|---|
| 1616 | [8] Brisco, T., "DNS Support for Load Balancing", RFC 1794, April
|
|---|
| 1617 | 1995.
|
|---|
| 1618 |
|
|---|
| 1619 | [9] Vixie, P. and D. Wessels, "Hyper Text Caching Protocol
|
|---|
| 1620 | (HTCP/0.0)", RFC 2756, January 2000.
|
|---|
| 1621 |
|
|---|
| 1622 | [10] Fan, L., Cao, P., Almeida, J. and A. Broder, "Summary Cache: A
|
|---|
| 1623 | Scalable Wide-Area Web Cache Sharing Protocol", Proceedings of
|
|---|
| 1624 | ACM SIGCOMM'98 pp. 254-265, September 1998.
|
|---|
| 1625 |
|
|---|
| 1626 | [11] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
|
|---|
| 1627 | for Message Authentication", RFC 2104, February 1997.
|
|---|
| 1628 |
|
|---|
| 1629 | [12] Netscape, Inc., "Navigator Proxy Auto-Config File Format",
|
|---|
| 1630 | March 1996,
|
|---|
| 1631 | <URL:http://www.netscape.com/eng/mozilla/2.0/relnotes/demo/proxy-
|
|---|
| 1632 | live.html>.
|
|---|
| 1633 |
|
|---|
| 1634 | [13] Gauthier, P., Cohen, J., Dunsmuir, M. and C. Perkins, "The Web
|
|---|
| 1635 | Proxy Auto-Discovery Protocol", Work in Progress.
|
|---|
| 1636 |
|
|---|
| 1637 | [14] Valloppillil, V. and K. Ross, "Cache Array Routing Protocol",
|
|---|
| 1638 | Work in Progress.
|
|---|
| 1639 |
|
|---|
| 1640 | [15] Microsoft Corporation, "Cache Array Routing Protocol (CARP)
|
|---|
| 1641 | v1.0 Specifications, Technical Whitepaper", August 1999,
|
|---|
| 1642 | <URL:http://www.microsoft.com/Proxy/Guide/carpspec.asp>.
|
|---|
| 1643 |
|
|---|
| 1644 | [16] Microsoft Corporation, "Cache Array Routing Protocol and
|
|---|
| 1645 | Microsoft Proxy Server 2.0, Technical White Paper", August
|
|---|
| 1646 | 1998,
|
|---|
| 1647 | <URL:http://www.microsoft.com/proxy/documents/CarpWP.exe>.
|
|---|
| 1648 |
|
|---|
| 1649 | [17] Lovric, I., "Internet Cache Protocol Extension", Work in
|
|---|
| 1650 | Progress.
|
|---|
| 1651 |
|
|---|
| 1652 |
|
|---|
| 1653 |
|
|---|
| 1654 | Cooper, et al. Informational [Page 29]
|
|---|
| 1655 | |
|---|
| 1656 |
|
|---|
| 1657 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1658 |
|
|---|
| 1659 |
|
|---|
| 1660 | [18] Cieslak, M. and D. Forster, "Cisco Web Cache Coordination
|
|---|
| 1661 | Protocol V1.0", Work in Progress.
|
|---|
| 1662 |
|
|---|
| 1663 | [19] Cieslak, M., Forster, D., Tiwana, G. and R. Wilson, "Cisco Web
|
|---|
| 1664 | Cache Coordination Protocol V2.0", Work in Progress.
|
|---|
| 1665 |
|
|---|
| 1666 | [20] Goutard, C., Lovric, I. and E. Maschio-Esposito, "Pre-filling a
|
|---|
| 1667 | cache - A satellite overview", Work in Progress.
|
|---|
| 1668 |
|
|---|
| 1669 | [21] Hamilton, M., Rousskov, A. and D. Wessels, "Cache Digest
|
|---|
| 1670 | specification - version 5", December 1998,
|
|---|
| 1671 | <URL:http://www.squid-cache.org/CacheDigest/cache-digest-
|
|---|
| 1672 | v5.txt>.
|
|---|
| 1673 |
|
|---|
| 1674 | [22] Cerpa, A., Elson, J., Beheshti, H., Chankhunthod, A., Danzig,
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| 1675 | P., Jalan, R., Neerdaels, C., Shroeder, T. and G. Tomlinson,
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| 1676 | "NECP: The Network Element Control Protocol", Work in Progress.
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| 1677 |
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| 1678 | [23] Cooper, I. and J. Dilley, "Known HTTP Proxy/Caching Problems",
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| 1679 | Work in Progress.
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| 1708 |
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| 1709 |
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| 1710 |
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| 1711 | Cooper, et al. Informational [Page 30]
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| 1712 | |
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| 1713 |
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| 1714 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
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| 1715 |
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| 1716 |
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| 1717 | Authors' Addresses
|
|---|
| 1718 |
|
|---|
| 1719 | Ian Cooper
|
|---|
| 1720 | Equinix, Inc.
|
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| 1721 | 2450 Bayshore Parkway
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| 1722 | Mountain View, CA 94043
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| 1723 | USA
|
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| 1724 |
|
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| 1725 | Phone: +1 650 316 6065
|
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| 1726 | EMail: icooper@equinix.com
|
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| 1727 |
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| 1728 |
|
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| 1729 | Ingrid Melve
|
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| 1730 | UNINETT
|
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| 1731 | Tempeveien 22
|
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| 1732 | Trondheim N-7465
|
|---|
| 1733 | Norway
|
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| 1734 |
|
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| 1735 | Phone: +47 73 55 79 07
|
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| 1736 | EMail: Ingrid.Melve@uninett.no
|
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| 1737 |
|
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| 1738 |
|
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| 1739 | Gary Tomlinson
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| 1740 | CacheFlow Inc.
|
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| 1741 | 12034 134th Ct. NE, Suite 201
|
|---|
| 1742 | Redmond, WA 98052
|
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| 1743 | USA
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| 1744 |
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| 1745 | Phone: +1 425 820 3009
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|---|
| 1746 | EMail: gary.tomlinson@cacheflow.com
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| 1747 |
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| 1767 |
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| 1768 | Cooper, et al. Informational [Page 31]
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| 1769 | |
|---|
| 1770 |
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|---|
| 1771 | RFC 3040 Internet Web Replication & Caching Taxonomy January 2001
|
|---|
| 1772 |
|
|---|
| 1773 |
|
|---|
| 1774 | Full Copyright Statement
|
|---|
| 1775 |
|
|---|
| 1776 | Copyright (C) The Internet Society (2001). All Rights Reserved.
|
|---|
| 1777 |
|
|---|
| 1778 | This document and translations of it may be copied and furnished to
|
|---|
| 1779 | others, and derivative works that comment on or otherwise explain it
|
|---|
| 1780 | or assist in its implementation may be prepared, copied, published
|
|---|
| 1781 | and distributed, in whole or in part, without restriction of any
|
|---|
| 1782 | kind, provided that the above copyright notice and this paragraph are
|
|---|
| 1783 | included on all such copies and derivative works. However, this
|
|---|
| 1784 | document itself may not be modified in any way, such as by removing
|
|---|
| 1785 | the copyright notice or references to the Internet Society or other
|
|---|
| 1786 | Internet organizations, except as needed for the purpose of
|
|---|
| 1787 | developing Internet standards in which case the procedures for
|
|---|
| 1788 | copyrights defined in the Internet Standards process must be
|
|---|
| 1789 | followed, or as required to translate it into languages other than
|
|---|
| 1790 | English.
|
|---|
| 1791 |
|
|---|
| 1792 | The limited permissions granted above are perpetual and will not be
|
|---|
| 1793 | revoked by the Internet Society or its successors or assigns.
|
|---|
| 1794 |
|
|---|
| 1795 | This document and the information contained herein is provided on an
|
|---|
| 1796 | "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
|---|
| 1797 | TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
|---|
| 1798 | BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
|---|
| 1799 | HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
|---|
| 1800 | MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
|---|
| 1801 |
|
|---|
| 1802 | Acknowledgement
|
|---|
| 1803 |
|
|---|
| 1804 | Funding for the RFC Editor function is currently provided by the
|
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| 1805 | Internet Society.
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| 1806 |
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| 1825 | Cooper, et al. Informational [Page 32]
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| 1826 | |
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| 1827 |
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| 1828 |
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| 1829 |
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