IPFW, IPFW2, and IP6FW allow the ruleset writer to add more than one rule with the same number. Here’s a command that lists rules with the same numbers:

IPFW/IPFW2: 

$ ipfw show | cut -f 1 -d ’ ’ | uniq –d
00100
00243

IP6FW: 

$ ip6fw show | cut -f 1 -d ’ ’ | uniq –d
00100
00243