6 ms·

Does anyone know why LAN Sync is normally turned off by default?

ComputerGuru 11y ago
Security reasons. It can be used to confirm whether or not a certain file exists on another PC on the network by observing where it's synced to/from. That said, there's nothing novel here. People have been doing this for decades, and extensions to the bittorrent protocol use it all the time to prioritize LAN seeds over internet seeds. In fact, I believe there was talk a while back about optimizing BT to prioritize peers and seeds on the same subnet/ISP as a way of mitigating ISP bandwidth concerns and whatnot.
- sleet 11y ago
  Facebook use bittorrent as part of their deployment process, they exploit rack and cluster affinity to improve performance [1]. [1] https://facebook.com//download/1411324735760067/devops.pdf https://facebook.com//download/1411324735760067/devops.pdf
  - toomuchtodo 11y ago
    ROCKS clustering software was doing this before Facebook. We'd use it to reinstall Redhat on ~6000 Linux nodes. Could reinstall the entire cluster in 15 minutes while still running jobs for end users.
  - gogopuppygogo 11y ago
    Twitter has been doing this for a while: https://blog.twitter.com/2010/murder-fast-datacenter-code-deploys-using-bittorrent https://blog.twitter.com/2010/murder-fast-datacenter-code-de...
- plorg 11y ago
  Perhaps your concern is slightly distinct, but the article addresses the discovery concerns you have given. Specifically, a LANSync peer can only request blocks for which it shares namespace authorization. Each distinct shared folder context (e.g. a folder shared between users, a whole Dropbox folder authorized for a single user on multiple computers) has a different namespace, and that namespace is associated with a keypair, issued by Dropbox. Block discovery and exchange is conducted over HTTPS, with each client and server having to use the key associated with the namespace of the block they wish to exchange. Since Dropbox clients/peers use SNI to identify the namespace, an eavesdropper on the network could know that two computers have access to the same namespace/folder (it is not clear from the post if the namespace contains any specific identifying information beyond its uniqueness), but not which files (or, more accurately, blocks) that namespace contained. A user who knew the key for a namespace could identify blocks being exchanged, but such a user would already have owned the Dropbox installation enough to have access not just to the list of files but to the files themselves.
parennoob 11y ago
I can say why it should be turned off by default -- because as a user, I don't want Dropbox knowing anything about computers on my network and relating IP addresses on the LAN to specific users. I'll take the long download times.
- justinsaccount 11y ago
  But you are still running dropbox on those computers on your LAN. What makes you think dropbox doesn't already know all about those computers?

Security reasons. It can be used to confirm whether or not a certain file exists on another PC on the network by observing where it's synced to/from. That said, there's nothing novel here. People have been doing this for decades, and extensions to the bittorrent protocol use it all the time to prioritize LAN seeds over internet seeds. In fact, I believe there was talk a while back about optimizing BT to prioritize peers and seeds on the same subnet/ISP as a way of mitigating ISP bandwidth concerns and whatnot.

sleet 11y ago
Facebook use bittorrent as part of their deployment process, they exploit rack and cluster affinity to improve performance [1]. [1] https://facebook.com//download/1411324735760067/devops.pdf https://facebook.com//download/1411324735760067/devops.pdf
- toomuchtodo 11y ago
  ROCKS clustering software was doing this before Facebook. We'd use it to reinstall Redhat on ~6000 Linux nodes. Could reinstall the entire cluster in 15 minutes while still running jobs for end users.
- gogopuppygogo 11y ago
  Twitter has been doing this for a while: https://blog.twitter.com/2010/murder-fast-datacenter-code-deploys-using-bittorrent https://blog.twitter.com/2010/murder-fast-datacenter-code-de...
plorg 11y ago
Perhaps your concern is slightly distinct, but the article addresses the discovery concerns you have given. Specifically, a LANSync peer can only request blocks for which it shares namespace authorization. Each distinct shared folder context (e.g. a folder shared between users, a whole Dropbox folder authorized for a single user on multiple computers) has a different namespace, and that namespace is associated with a keypair, issued by Dropbox. Block discovery and exchange is conducted over HTTPS, with each client and server having to use the key associated with the namespace of the block they wish to exchange. Since Dropbox clients/peers use SNI to identify the namespace, an eavesdropper on the network could know that two computers have access to the same namespace/folder (it is not clear from the post if the namespace contains any specific identifying information beyond its uniqueness), but not which files (or, more accurately, blocks) that namespace contained. A user who knew the key for a namespace could identify blocks being exchanged, but such a user would already have owned the Dropbox installation enough to have access not just to the list of files but to the files themselves.

parennoob 11y ago

I can say why it should be turned off by default -- because as a user, I don't want Dropbox knowing anything about computers on my network and relating IP addresses on the LAN to specific users. I'll take the long download times.

justinsaccount 11y ago
But you are still running dropbox on those computers on your LAN. What makes you think dropbox doesn't already know all about those computers?