securing Ubuntu and firewall

[Mike Bird]

On Sat, 2006-02-25 at 11:04, H.S. wrote:
> Alan McKinnon wrote:
> > First, we should get our terminology right. The Linux kernel doesn't 
> > implement a firewall, it's a packet filter. So you can't do 
> > intelligent firewalling related to the content of what's in a packet, 
> > you can only ACCEPT or REJECT a packet based on the IP protocol, 
> > port, source/destination address, related to an already accepted 
> > connection, etc.
> 
> Just a minor addition (from my limited knowledge of internal working of
> IP/TCP:
> also the content of the TCP/IP flags. You can filter packets based
> various flag configurations.

You can also use iptables to redirect certain traffic for
further filtering, as in transparent squid proxy caching.

You can also theoretically use iptables to redirect certain
traffic to userspace for further processing using the QUEUE
target although I have not yet tried this.

--Mike Bird