Interplanetary Network Indexers provides an infrastructure layer for 'content routing' - learning who has what pieces of content addressed data. IPNI is a scalable, federated system that fills the same role as a DHT. It is used by Filecoin and IPFS, and offers a neutral interface for publication and querying.

You can see an example endpoint for querying IPNI at https://cid.contact/.

Documentation for how a node can publish what content it has, and the semantics for querying is maintained at https://github.com/ipni/specs