Maximum capacity of IPTABLES rules, firewall rules.

normally 32 bit system and integer value of count of  IP rules apprx.. some millions.

BUT I tested it myself  on my SERVER.      after 56 000  , (56 Thousands)  it becomes  slower.

My server has SSD disk and 16 GB memory.

But this is changable.  If you do good firewall  script, You can  use  2 million IP rules with best performance.