Types of peer-to-peer networks

• Directory-based (e.g., original Napster design)
• Unstructured (e.g., Gnutella, Kazaa, BitTorrent)
• Structured (e.g., distributed hash tables)

Routing overlays

• Overlay networks
• Connect most P2P systems

Challenges in peer-to-peer

• Legal issues, free riding, fast response to queries, peers coming and going over time, reliability, security,