problem on ipfw using mac addresses

[h bagade]

Hi all,

I have a problem using ipfw firewall. I have a topology connected as below:

A(192.168.1.55) ----- (192.168.1.1)my_sys(192.168.2.1)
-------(192.168.2.12)B

I've set the rule "ipfw add 1 deny icmp from any to any" on my_sys, which
works correctly. I can't ping from A to B by the rule. Then I've added mac
part to the rule as the format of "ipfw add 1 deny icmp from any to any ma
any any" which seems the same as before but after that I could ping the B
from A.
What's the reason? I'm really confused with what I saw! Is it a bug?

Any hints or suggestions are really appreciated.