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Internet Cache Protocol (ICP), version 2 (RFC2186)

IP.com Disclosure Number: IPCOM000002745D
Original Publication Date: 1997-Sep-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 7 page(s) / 17K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D. Wessels: AUTHOR [+2]

Abstract

This document describes version 2 of the Internet Cache Protocol (ICPv2) as currently implemented in two World-Wide Web proxy cache packages[3,5]. ICP is a lightweight message format used for communicating among Web caches. ICP is used to exchange hints about the existence of URLs in neighbor caches. Caches exchange ICP queries and replies to gather information to use in selecting the most appropriate location from which to retrieve an object.

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This is the abbreviated version, containing approximately 16% of the total text.

Network Working Group D. Wessels

Request for Comments: 2186 K. Claffy

Category: Informational National Laboratory for Applied

Network Research/UCSD

September 1997

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 version 2 of the Internet Cache Protocol

(ICPv2) as currently implemented in two World-Wide Web proxy cache

packages[3,5]. ICP is a lightweight message format used for

communicating among Web caches. ICP is used to exchange hints about

the existence of URLs in neighbor caches. Caches exchange ICP

queries and replies to gather information to use in selecting the

most appropriate location from which to retrieve an object.

This document describes only the format and fields of ICP messages.

A companion document (RFC2187) describes the application of ICP to

Web caches. Several independent caching implementations now use ICP,

and we consider it important to codify the existing practical uses of

ICP for those trying to implement, deploy, and extend its use for

their own purposes.

1. Introduction

ICP is a message format used for communicating between Web caches.

Although Web caches use HTTP[1] for the transfer of object data,

caches benefit from a simpler, lighter communication protocol. ICP

is primarily used in a cache mesh to locate specific Web objects in

neighboring caches. One cache sends an ICP query to its neighbors.

The neighbors send back ICP replies indicating a "HIT" or a "MISS."

In current practice, ICP is implemented on top of UDP, but there is

no requirement that it be limited to UDP. We feel that ICP over UDP

offers features important to Web caching applications. An ICP

query/reply exchange needs to occur quickly, typically within a

second or two. A cache cannot wait longer than that before beginning

to retrieve an object. Failure to receive a reply message most

likely means the network path is either congested or broken. In

either case we would not want to select that neighbor. As an

indication of immediate network conditions between neighbor caches,

ICP over a lightweight protocol such as UDP is better than one with

the overhead of TCP.

In addition to its use as an object location protocol, ICP messages

c...