ICP is a Web caching protocol 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.

ICP Documentation

• RFC 2186 ICPv2 protocol specification.
• RFC 2187 ICPv2 application specification.
• Currently defined opcodes and flags. This document includes protocol additions since the above RFC's were published.
• Earliest known ICP documentation
• ICP and the Squid Web Cache

Implementation

The following products (and non-products) implement ICP:

• Squid
• Network Appliance
• Microsoft Proxy
• Cisco Cache Engine
• Novell Internet Caching System Volera
• CacheFlow BlueCoat
• iMimic DataReactor
• more?

Tools

Some tools for testing ICP

• icp-test.pl sends ICP queries to a set of caches. It keeps only one outstanding query at a time, and waits up to two seconds for all ICP replies to arrive.
• udp-banger.pl sends ICP queries to a single cache as quickly as it can.

Related Stuff

These other inter-cache protocols and algorithms are an alternative to ICP.

• HTCP -- Hypertext Caching Protocol
• CARP -- Cache Array Routing Protocol
• Cache Digests

Unrelated Stuff

• Insane Clown Possie