Handling a simple dos attack

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We occasionally get hit by a miscreant client who will open a large number of connections and leave them in an open/wait state, using all the available children. I have more than adequate resources for normal traffic. Limiting the number of connections from a single source isn't an option because the nature of our business means that we often have many connections from a single IP. Right now, we deal with the problem by banning the offending IP in our firewall and restarting Apache.  

How do other people handle this? Is there something more creative I can do inside Apache? I'm thinking of the way that Postfix handles stress, where it can decrease time-out values under high load to drop connections more quickly and keep resources free (I know, it isn't exactly comparable to http, but still ... ). Can I do something similar with Apache? Suggestions or pointers to the right docs would be greatly appreciated.