Someone asked me this recently and I had no answer for it. I know this is kind of an open-ended question but is there a limit on the numnber of rules you can install in a table/chain? If so, how can I find it out? I guess it will vary across machines.
The theoretical upper limit of maximum number of rules for a 32-bit environment would be somewhere around 38 million, but you could also construct a rule that is so crowded with matches that even it won't fit, so the lower limit of max rules is 0.
According linuxquestions.org, on a 32-bit machine, IPTables will support around 25,000 rules. Going beyond that, especially from 27,000, things start to get flaky.