Peer-to-Peer Frequently Asked Questions

N.B. This FAQ focuses on the very nebulous term "p2p system". There's not a single answer that maps exactly to all peer-to-peer systems; this FAQ does its best to provide a general answer when possible, and provide concrete examples where it makes sense.

Sounds great, but will it scale?

Yes. It is rare to find a p2p service that does not scale. They are distributed systems by design, and most distributed systems are meant to scale. You could say, then, that many distributed systems take cues from p2p systems in order to scale properly. As a good example, Skype was built by the same engineers who built Kazaa, and Skype internally used p2p distribution in order to alleviate the load from any single node, and to save costs. Bittorrent also thrives in situations where there are a high number of peers.

Like centralized systems, performance will suffer if the load is not distributed. A torrent file with only one seed and thousands of leechers would struggle to initially share to the first wave of peers. Unlike a centralized system though, once that first wave of peers downloads a copy, the bandwidth for that torrent data to be served grows exponentially.

If websites are hosted on p2p, what happens when no peers are online?

The same result as when a centralized website goes down: it isn't available.

The difference is that peer-to-peer networks distribute the power to host. I could run a peer serving my website on a server. Instantly I have the same website availability as a traditional centralized website. The difference is that there may be many peers in the swarm that are also hosting my website, so if my server goes down, the site will continue to be accessible through those seeding peers.

What about security? Somebody could share a hacked version of a p2p website?

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What about privacy? Everybody in the p2p network can see what I am looking at.

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p2p is great, but sometimes you need a single authoritative source of truth

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What if nazis take over the p2p network?

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What areas do modern p2p apps still struggle with?

Apps still seem to have a hard time managing resources, like CPU and network bandwidth. If an app naively tries to download and replicate ALL of the data it sees, it's easy for it to overwhelm the machine it's running on. Many apps still have a ways to go in offering good controls for CPU and bandwidth use.