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Internet Cache Protocol (icp)

WG Name Internet Cache Protocol
Acronym icp
State BOF Concluded
Charter charter-ietf-icp-01 Approved
Document dependencies
Personnel Chair Duane Wessels
Chat Room address

Charter for Working Group


ICP is a lightweight message format used for communicating among
WWW caches. ICP is primarily used in a cache mesh to locate
specific WWW objects in neighbor caches. A cache in such a mesh
may have numerous choices for resolving a URL request. ICP is used
to assist in selecting the most appropriate location. One cache
will send an ICP query to its neighbors. The neighbors will send
back ICP replies indicating a HIT'' or aMISS.'' All current
ICP implementations use UDP as the transport. Messages consist of a
20-byte fixed header and a variable-sized payload. The payload is
normally a URL string. ICP has been in use since 1995. We
estimate there are approximately 3000 Web caches in operation that
support ICP.

The purpose of this BOF is to propose formation of the ICP Working
Group. The goal of the ICP working group is only this: To
document existing, deployed ICP version 2 implementations as an
Informational RFC. There will be two documents: one describing the
protocol and message format, and another describing how ICP is
currently applied to Web cache meshes. This will be the second ICP

For more information, please visit the ICP Development page at