Squid is particularly good at communicating with other caches and proxies. Numerous inter-cache communication protocols are supported, including ICP (Inter-Cache Protocol), Cache-Digests, HTCP (Hyper-Text Cache Protocol) and CARP (Cache Array Routing Protocol). Each of these protocols has specific strengths and weaknesses; they are more suited to some circumstances than others.
In this chapter we look at each of the protocols in detail. We also look at the different ways that you can structure your cache hierarchy, and work through the config options that effect cache hierarchies.