SNORT sensor on FreeBSD Bridged IPFW Firewall!

["Athena" <mailinglists () presstekeurope com>]

Hi Group
 
I have just finished setting up snort console box with two snort sensors
running on FreeBSD and all seems to be working perfectly!
 
However I would be grateful if somebody would be able to help me with one
question:
 
Firstly here is a quick rundown of my LAN.
 
I have a FreeBSD-6.0 bridged firewall with three interfaces. The first two
are configured in a bridge (passed through IPFW) with no IP addresses and
the third is a management interface with one public IP Assigned. 
 
One side of the bridge connects into a DSL router and the other side &
management interface connect into a HUB (Not Switch) where various other
FreeBSD systems with public IPs sit:
 
1]    POSTFIX SMTP
2]    PRIMARY DNS 
3]    SNORT CONSOLE
4]    NATD SERVER
 
I currently have a two sensors running on both sides of the NATD Server
which logs traffic both on my private LAN and firewalled public side; this
works perfectly, however its only providing me information on my trusted
network and I still have no idea what's happening on the untrusted side.
 
So this leads me onto my question:
 
Is it possible to install a SNORT sensor on the internet facing interface of
my FreeBSD Bridge and if I did would it capture packets before they are
passed through IPFW? Or, as I suspect would it be better if I install a TAP
between my router and the internet facing interface?
 
Hope somebody can help & many thanks in advance.
 
Regards
Athena
 
 
 

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