I don't quite understand the last calculation. "if all 65535 connections on an IP were open" => I'm guessing you mean ports "the biggest Tor Guard has 0.91% Guard probability" => percentage of all entries into the network handled by this guard => 0.91% of all user connections but how many user connections are there at a time? and then don't understand how probability and ports availability can be combined? Please elaborate. Thanks On Mon, 18 Dec 2017 at 23:11 teor <teor2345@gmail.com> wrote:
On 19 Dec 2017, at 08:38, Toralf Förster <toralf.foerster@gmx.de> 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/9844B981A80B3E4B50897098E2D65167E6AEF1...
T
-- Tim Wilson-Brown (teor)
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