Circuit Level Gateway & Filtering!?
Thx Antony
But:
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Circuit level filtering means packet filtering - what netfilter does - in
other words you filter packets based on where they've come from and where
they're going to (IP addresses), and on *assumptions* about what the TCP/UDP
port numbers mean, rather than based on anything that's actually inside the body of the packets (data).
I read it's sth more than packet filtering, and it work on session
layer. Working on session layer is a little hard for me to underestand. I'm looking for some example.
I guess ESTABLISHED state option of iptables make it work on such
level, but I'm not sure.
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Application level filtering means proxies - software which can understand protocols like http, smtp, pop3, ftp, irc.... and look at the data and commands which are being transferred between machines, then base the filtering decisions on that (as well as IP addresses and hostnames).
Gateway simply refers to a machine which is in the path between your network and the outside world - can mean anything from a simple router with no filtering capabilities to a multi-protocol proxy server with intrusion detection.
Thx but, I meant "Circuit Level gateway" not a simple gateway I mean IP(or network level).
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Netfilter (iptables) is a stateful packet filter, and therefore operates at
layers 3/4 of the OSI model - the network layers. It does not meaningfully
operate at layer 7 - the application layer.
But I think matching RELATED state of ftp data connection means working on layer 7.
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If you want realistic application layer filtering on a linux system you need
proxy applications like sendmail/exim/apache/squid/frox. Netfilter won't do
it for you.
So u mean there's no such matching module or action in Netfilter.
P.S. Below is what I read about Circuit Level (Filtering and Gateway). But they are alittle ambiguous!
Regards__Radien__
http://www.pc-help.org/www.nwinternet.com/pchelp/lockdown/claims/firewalls.htm
http://csrc.nist.gov/publications/nistpubs/800-10/node53.html&e=7317
http://www.pcstats.com/articleview.cfm?articleid=1450&page=5
http://www.firewall-software.com/firewall_faqs/types_of_firewall.html