RFC 2186 (rfc2186) - Page 1 of 9
Internet Cache Protocol (ICP), version 2
Alternative Format: Original Text Document
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 (RFC 2187) 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."
Wessels & Claffy Informational