> On 19 Dec 2017, at 08:38, Toralf Förster <toralf.foerster@xxxxxx> wrote: > > On 12/17/2017 10:24 PM, teor wrote: >> Using 256 per IP is probably reasonable. > > Is this a rather arbitrary limit or does this limit fit the use of NATed addresses entirely ? That's an arbitrary safe upper bound. The number of active connections that can be NATed per IP address is limited by the number of ports: 65535. (Technically, it's 65535 per remote IP address and port, but most NATs don't have that much RAM or bandwidth.) Also, genuine users behind a NAT would likely have multiple Tor and non-Tor connections open. And spare ports are needed for NAT to manage port churn and the TCP delay wait state on connection close. To be more precise: * if all 65535 connections on an IP were open to the Tor network, and * the biggest Tor Guard has 0.91% Guard probability[0], then * it would expect to see 597 connections. Feel free to do the sums for your own guard's probability. (We are aware of the issue, and we are working on a more permanent fix.) [0]: https://atlas.torproject.org/#details/9844B981A80B3E4B50897098E2D65167E6AEF127 T -- Tim Wilson-Brown (teor) teor2345 at gmail dot com PGP C855 6CED 5D90 A0C5 29F6 4D43 450C BA7F 968F 094B ricochet:ekmygaiu4rzgsk6n xmpp: teor at torproject dot org ------------------------------------------------------------------------
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