Peer communication protocols

We have learned about configuring Squid to be a part of a cache hierarchy. When many proxy servers are a part of cache hierarchy, they need to communicate to share information about the objects present in their cache so that neighbors can utilize these cached objects as hits. For communication among peers, Squid implements ICP, HTCP, and Cache Digest protocols. Later on, we'll have a brief look at ICP, HTCP, and Cache Digest protocols.

Internet Cache Protocol

ICP or Internet Cache Protocol is a simple web-caching protocol used to query proxy servers (cache peers) about the existence of a particular object in their cache. Depending on the replies received from the neighbors, Squid will decide the forwarding path for the particular request.

As we saw in the peer selection algorithms, ICP is also used to calculate the round trip time and also for detecting dead peers in a hierarchy. The round trip time calculation is an important measure as it can help Squid in dynamically...