Neil Moore-Smith wrote:
> This is obviously a stupid question to the cognoscenti, but what do the
> "input" and "output" firewall options on the ipfwadm command actually, or
> are meant to be used for?
The input firewall controls which packets can be received, while the
output firewall controls which packets can be sent.
> I have a LRP firewall set up up with machine "A" on the internal network
> side. With no firewalling (i.e. accept all) I can ping it, read it's web
> pages etc from the external side. I can then use ipfwadm -F to block http
> (for example) from a specific external host. This works fine. If I then
> reinstate forwading and use ipfwadm -I with similar parameters, I get the
> same result. So what's the difference between F, I, and O? Is F simply a
> combination of I and O for ease of use?
Packets which are sent via a router have to pass all three firewalls
in the order `input -> forwarding -> output'.
The input firewall can be used to prevent certain packets from being
sent to the host itself. Likewise, the output firewall can be used to
prevent certain packets from being sent from the host (although the
output firewall is definitely the least useful of the three).
--
Glynn Clements <[EMAIL PROTECTED]>
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