[plug] configing iptables

[bob]

Ok, I "think" I'm getting my head around iptables :). I still have some
Q's though so hopefully you guys can give me some hints. BTW, I've tried
a bunch of rule scripting tools but they either don't do what I want or
are broken for debian so I'm trying to do this by hand.

OK, given that everything on eth0 (192.168.0.0/24) is trusted, is it
safe to do the following (and/or will it do what I expect)?

iptables -A INPUT -i eth0 -p all -j ACCEPT 
iptables -A OUTPUT -o eth0 -p all -j ACCEPT

... bunch of rules about services and ppp0 followed by...
 
iptables -A INPUT -p all -s 192.168.0.0/16  -i ppp0 -j DROP
iptables -A INPUT -i ppp0 DROP

ie, everything on eth0 is ok and anything arriving on ppp0 purporting to
be 192.168... is to be dropped and everything else . 

Is that ok? or is there a better way of doing what I want. 

Thanks.
-- 
bob
Cave canem...te necet lingendo.