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I set out to do an experiment that required me to do searches without cookies or location biasing the results. I wanted location, however to always be somewhere in USA, so I set ExitNodes accordingly.

If I open a new tab, the exit node is the same as before. If I closed the window, i.e., all tabs, and open a new one, I still get the same exit node.

If I select "new circuit" from the menu, I get a different middle node, but the ExitNode does not change.

If I exit Tor and re-launch, I do get a different ExitNode.

Is this a bug? Is there a way to force a new ExitNode, or change the ExitNodes restrictions, without shutting down and relaunching?

Version 6.0.5 on MacOS 10.12

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If I open a new tab, the exit node is the same as before. If I closed the window, i.e., all tabs, and open a new one, I still get the same exit node.

The browser uses an isolation method, to isolate connections by the "first party" domain (e.g. torproject.org), so all tabs with torproject.org in the address bar will use the same circuit. If both tabs were for the same site, it is intended that it uses the same circuit. It will also keep these circuits open for these sites while they are in use

If I select "new circuit" from the menu, I get a different middle node, but the ExitNode does not change.

"New Circuit" or "New Identity" do not guarantee a new exit, it only guarantees that it will use a "new" (previously unused, although possibly pre-built) circuit. It's entirely possible that you would pick the same exit twice in two distinct circuits, due to the way weighting influences the path selection.

Is there a way to force a new ExitNode

Not really, there are some ugly ways to do it but they'd require significant work on your part. There's no real advantage to most Tor users to force a "new" exit node (and infact it could be significantly disadvantageous to anonymity in certain circumstances).

or change the ExitNodes restrictions, without shutting down and relaunching?

You could use the Control Port to reconfigure Tor's ExitNodes configuration, or you can edit the torrc and send a hangup signal (SIGHUP) to the tor process. These would allow you to reconfigure the choice of exits but the choice would be random, another option instead of using ExitNodes might be to use a MapAddress directive with the .exit notation (that is, and should be, disabled by default because of it's serious security and anonymity implications but it will work through a custom MapAddress).

Consider also that there are already tools that are designed to perform an action across a set of exit relays, like ExitMap, which allows you to look for anomalous behaviour on specific exits.

  • "New circuit for this site" is misleading then. Only part of it is new, and if you are trying to keep the site from associating your next move with your previous, then the part you want new is the part that doesn't change. In my experiment, what was actually wanted was exactly that: to ensure that the phenomena being observed could not be affected by the remote site "thinking" the GET was from the same source. I guess I should read up on Control port (but I don't have time, waah) – WGroleau Oct 19 '16 at 4:34
  • The web server being fetched from has no knowledge of middle node nor entry node, so what benefit is changing those? – WGroleau Oct 19 '16 at 4:36
  • No, new circuit will never disassociate old actions from new. This is what new identity is for. Other Tor users will also use that exit to access the site, both will be indistinguishable. This is the crux of the anonymity provided. Changing exits does not provide anonymity or a new identity when they can track application level state between visits. – cacahuatl Oct 19 '16 at 4:42
  • New identity is as much a pain as killing the app and relaunching. – WGroleau Oct 19 '16 at 5:03
  • It's also the only way to effectively clear application level state, by resetting it to a generic base state from which all users start. Without resetting the state, picking a new exit does approximately nothing to stop a site from tracking user activity. – cacahuatl Oct 19 '16 at 11:02

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