ipfw -- why need to let icmp out that I already let in?

[freebsd at dreamchaser.org]

Are you sure you don't have some other rule which is letting those returned 
packets out the other port?  When I substitute your rule for my two:
   ipfw delete 10531
   ipfw delete 10532
   ipfw add 10531 allow icmp from any to any icmptypes 0,3,11,12 in

The returning packets are dropped inside the firewall.  (traceroute still 
works from the firewall itself, but not from an internal machine).

Gary


Dan Nelson wrote:
> In the last episode (Oct 31), Ivan Voras said:
>> freebsd at dreamchaser.org wrote:
>>
>>> add 10510 allow icmp from any to any out via oif() keep-state
>> I don't think ICMP is stateful :)
>>
>> You need both in and out rules for ICMP because the logical responses
>> to packets can't be reliably connected into a single communication.
> 
> I use "allow icmp from any to any icmptypes 0,3,11,12 in"
> 
> those types being "echo reply", "destination unreachable",
> "time-to-live exceeded", and "IP header bad".
>