> I take it to mean that packets from host2 to host 3 were NOT accepted by this > rule? ... What do the counters for the rule say? ( iptables -L -n -v -x ). yes, I already look after the counter. A paket from host2 to host3 dont increase the counter. > What other rules exist that might affect said packets? -- I note the above is > an ADD. Could rules farther up the FORWARD chain have already > accepted/denied the said packets? this was only a example. I tested also on a other pc, with has normal no rulesset to be sure. > FYI -- I just tested this by inserting a double negative rule in my firewall > > iptables -I tcp_packets -p tcp -s ! {internal_lan} -d ! {internal lan ip} > --dport 25 -j allowed > > and sending myself an email from outside. The packet counter incremented > appropriately. Sorry, but why are you able to send with this rule a mail from outside to a mailserver in your internal network? I suppose, that with the "-d ! {internal lan ip}" it ist not possible to send a paket to your mailserver. > well... my two cents :-) > > iptables -A FORWARD -s host1 -d host2 -j DROP well sorry it is not that easy as it seems. The rule should forward pakets to a user-chain only if host1 ist not the source and host2 are is not the destination. I also tested with the 2.6.7 kernel and 1.2.11, so I can exclude this. -- Supergünstige DSL-Tarife + WLAN-Router für 0,- EUR* Jetzt zu GMX wechseln und sparen http://www.gmx.net/de/go/dsl