1. A computer implemented method of indexing location of content cached within an IP-based network comprising: (a) intercepting data traffic flowing from a source node to a destination node in the network, the data traffic including content to be cached at the destination node, (b) extracting identity information for the content and associated destination location information for the destination node where the content in the data traffic is to be cached from the data traffic, (c) generating a mapping from the content identified by the extracted identity information to the destination node identified by the associated destination location information, (d) storing the mapping in a content index database, wherein the database provides an instance mapping containing a list of destination nodes at which the content has been cached, the instance mapping being provided in response to an instance request containing the identity information for the content, and (e) advertising the extracted content identities to which mappings are stored in the content index by sending advertising messages to a predetermined location in the network.