One way to do this structured routing

• Assign each node each node an id from space
• eg. 128 bits: SHA-1 salted hash of IP address
• build up a ring: circular hashing
• assign nodes into this space

Value

• diversity of neighbors
• even coverage of space
• less chance of attack?
  
  
  

Why “hash tables”?

• Stored named objects by hash code
• Route the object to the nearest location in space
• key idea: nodes and objects share id space

How do you find an object without its name?

• Close names don’t help because of hashing

Cost of churn?

• In most P2P apps, many joins and leaves

Dangers

• Sybil attacks: one node becomes many
• id attacks: can place your node wherever
• Solutions hard to come by
  • crytpo puzzles / money for IDs?
  • Certification of routing and storage?

Many routing frameworks in this spirit

• Very popular in late 90s early 00s
• Pastry, Tapestry, CAN, Chord, Kademlia