How many rules can iptables support?

Solution 1:

Quote from Jan Engelhardt

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.

http://www.spinics.net/lists/netfilter/msg51895.html

Solution 2:

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.