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64 lines
2.3 KiB
Plaintext
64 lines
2.3 KiB
Plaintext
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1. Overview
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We should rate limit the volume of stream creations at exits:
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2.1. Per-circuit limits
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If a given circuit opens more than N streams in X seconds, further
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stream requests over the next Y seconds should fail with the reason
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'resourcelimit'. Clients will automatically notice this and switch to
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a new circuit.
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The goal is to limit the effects of port scans on a given exit relay,
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so the relay's ISP won't get hassled as much.
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First thoughts for parameters would be N=100 streams in X=5 seconds
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causes 30 seconds of fails; and N=300 streams in X=30 seconds causes
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30 seconds of fails.
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We could simplify by, instead of having a "for 30 seconds" parameter,
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just marking the circuit as forever failing new requests. (We don't want
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to just close the circuit because it may still have open streams on it.)
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2.2. Per-destination limits
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If a given circuit opens more than N1 streams in X seconds to a single
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IP address, or all the circuits combined open more than N2 streams,
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then we should fail further attempts to reach that address for a while.
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The goal is to limit the abuse that Tor exit relays can dish out
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to a single target either for socket DoS or for web crawling, in
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the hopes of a) not triggering their automated defenses, and b) not
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making them upset at Tor. Hopefully these self-imposed bans will be
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much shorter-lived than bans or barriers put up by the websites.
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3. Issues
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3.1. Circuit-creation overload
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Making clients move to new circuits more often will cause more circuit
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creation requests.
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3.2. How to pick the parameters?
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If we pick the numbers too low, then popular sites are effectively
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cut out of Tor. If we pick them too high, we don't do much good.
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Worse, picking them wrong isn't easy to fix, since the deployed Tor
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servers will ship with a certain set of numbers.
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We could put numbers (or "general settings") in the networkstatus
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consensus, and Tor exits would adapt more dynamically.
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We could also have a local config option about how aggressive this
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server should be with its parameters.
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4. Client-side limitations
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Perhaps the clients should have built-in rate limits too, so they avoid
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harrassing the servers by default?
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Tricky if we want to get Tor clients in use at large enclaves.
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