ipfw: question about keep-state on icmp

[Geert Hendrickx]

Hi, 

this is a fragment of my ipfw-config which should allow me to ping 
others, but not allow others to ping me: 

00092 allow icmp from me to any keep-state
65535 deny ip from any to any

Indeed, other hosts can't ping me... UNLESS I am pinging them at the 
same time!  This is of course a result of keeping the state of icmp-
traffic between these two hosts, and I can avoid this by changing it to:

00091 deny icmp from any to me icmptype 8    <-- deny ping request to me
00092 allow icmp from me to any keep-state

(icmptype 8 = ping request) 

But then I don't see the use for keep-state in 00092 anymore...  The
following seems equally valid to me: 

00091 allow icmp from me to any
00092 allow icmp from any to me icmptype 0   <-- allow ping reply to me

So what am I missing?  

And are errors as in the first example also possible with
tcp-connections, e.g. ssh?  

GH