RFC 2187 (rfc2187) - Page 1 of 24

Application of Internet Cache Protocol (ICP), version 2

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Network Working Group                                          D. Wessels
Request for Comments: 2187                                      K. Claffy
Category: Informational                   National Laboratory for Applied
                                                    Network Research/UCSD
                                                           September 1997

        Application of Internet Cache Protocol (ICP), version 2

Status of this Memo

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

Abstract

   This document describes the application of ICPv2 (Internet Cache
   Protocol version 2, RFC 2186) to Web caching.  ICPv2 is a lightweight
   message format used for communication among Web caches.  Several
   independent caching implementations now use ICP[3,5], making it
   important to codify the existing practical uses of ICP for those
   trying to implement, deploy, and extend its use.

   ICP queries and replies refer to the existence of URLs (or objects)
   in neighbor caches.  Caches exchange ICP messages and use the
   gathered information to select the most appropriate location from
   which to retrieve an object.  A companion document (RFC 2186)
   describes the format and syntax of the protocol itself.  In this
   document we focus on issues of ICP deployment, efficiency, security,
   and interaction with other aspects of Web traffic behavior.

Table of Contents

   1.   Introduction.................................................  2
   2.   Web Cache Hierarchies........................................  3
   3.   What is the Added Value of ICP?..............................  5
   4.   Example Configuration of ICP Hierarchy.......................  5
     4.1. Configuring the `proxy.customer.org' cache.................  6
     4.2. Configuring the `cache.isp.com' cache......................  6
   5.   Applying the Protocol........................................  7
     5.1. Sending ICP Queries........................................  8
     5.2. Receiving ICP Queries and Sending Replies.................. 10
     5.3. Receiving ICP Replies...................................... 11
     5.4. ICP Options................................................ 13
   6.   Firewalls.................................................... 14
   7.   Multicast.................................................... 14
   8.   Lessons Learned.............................................. 16
     8.1. Differences Between ICP and HTTP........................... 16



Wessels & Claffy             Informational
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