IPFS combines several foundational P2P concepts into a coherent stack:

Content addressing via CIDs: every piece of data is identified by its Content Identifier. Files are chunked into blocks, organized into a Merkle DAG (UnixFS), and the root CID identifies the whole file.

Bitswap: a block exchange protocol where peers request blocks by CID and track per-peer ledgers of bytes sent/received. This implements swarming for content-addressed blocks.

Kademlia DHT: the Amino DHT, one of the largest Kademlia networks, used for provider record publication and peer routing.

IPNS: mutable pointers over immutable data; a signed record in the DHT maps a public identity key to a CID.

Pinning: explicit durable retention. Pinning services (Pinata, web3.storage) provide persistent availability.

Gateways: HTTP-to-IPFS bridges for browser access. Trustless gateways serve verified blocks rather than requiring trust in the gateway operator.

CAR files: Content Addressable aRchive format for bundling blocks for efficient transport and backup.

IPFS uses libp2p for all networking.

Filecoin adds economic incentives to IPFS:

Storage market: clients pay storage providers (miners) FIL tokens to store data for a specified duration via on-chain deals.

Proof-of-Replication (PoRep): a cryptographic proof that the provider has created a unique physical copy of the data.

Proof-of-Spacetime (PoSt): periodic proofs that the data is still being stored, submitted to the blockchain.

Retrieval market: a separate market for serving data, incentivizing bandwidth alongside storage.

FVM (Filecoin Virtual Machine): smart contracts on Filecoin for programmable storage deals, data DAOs, and cross-chain bridges.

Filecoin demonstrates that Storage and Distribution can be backed by verifiable economic commitments rather than just goodwill or bilateral tit-for-tat.

An alternative to Bitswap for transferring large DAG subsets efficiently:

The requester specifies a selector (a DAG traversal query describing what to fetch).

The responder streams matching blocks in a single round trip.

Much more efficient than Bitswap for large directories, datasets, and Filecoin retrieval.

IPFS is the flagship application of Content Addressing, Overlay Networks, and libp2p. Identity is used for IPNS, UCAN-based authorization, and Filecoin miner identity. Security considerations include DHT poisoning, content availability attacks, and gateway trust. Privacy is a concern: requesting a CID from the DHT reveals your interest. Compliance applies to gateway and pinning service operators. Testing uses Testground for large-scale network simulation.