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+1. Overview
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+
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+ We should rate limit the volume of stream creations at exits:
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+
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+2.1. Per-circuit limits
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+
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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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+
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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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+
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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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+
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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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+
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+2.2. Per-destination limits
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+
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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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+
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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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+
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+3. Issues
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+
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+3.1. Circuit-creation overload
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+
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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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+
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+3.2. How to pick the parameters?
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+
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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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+
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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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+
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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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+
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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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+
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+4. Client-side limitations
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+
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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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+
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+ Tricky if we want to get Tor clients in use at large enclaves.
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+
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