Transparent firewall, to capture Netflow data.

  • I have a PIX 515E at a customer site and need to track data flow through it.  I am unable to use netflow with it and was thinking of using pfSense as a transparent firewall/Bridge (I understand how to set that up.  Read doc.) between my network and the PIX.  I would then use pflowd to push the flow data to a PC.  Unsure of how this might work.  Would using pfsense as a router instead of transparent firewall be better since traffic needs to go back out the LAN interface or should I use an OPT1 interface to somehow pass that data?

    PIX  Private ( –- ( Gateway( int WAN [pfsense] int LAN (


  • Got it working.  Traffic is flowing but flow data going to an IP does not seem accurate.  Wondering if it would be better to put a NIC (OPT1) and assign it an different subnet connect a PC on it with a Netflow collector.

    Netflow collector shows traffic coming from LAN interface even though bridged with WAN.

  • Some really weird statistics from pftop.  This is realtime downloading 1.5 gb file where windows is saying I am pulling down at about 473KB/Sec but pftop is showing different numbers.  the netflow data also looks completely out of whack.

    473KB/Sec = 3.8748

    tcp   In        989K 1522K  982K 2063M  4:4  2089K  2150 86400 46
    tcp   Out        989K 1522K  982K 2063M  4:4  2089K  2150 86400 37

    Maybe I do not understand what it means by 989K. Is netflow adding the in and out?  It makes sense since if you cut that number in half it is my actual rate.  I have to test but if ntop is attached to the LAN, I get high numbers.  If attached to WAN, it is accurate.  Anyone know how pflowd is associated with which interface?

    My DSL line is 6Mb/756Kb

    RRD graphs show correct.

    Traffic graphs are accurate.  No throughput showing for either WAN or LAN.  Maybe as a router this would work.  A bummer beacuse it would be great to be able to take a little box to a customer site and throw it in between the network and the firewall to do analysis.

    pfSense firewall and pfSense bridge RRD graphs are the same.  nTop looks accurate but would prefer to use netflow to a collector for reporting and historical analysis.

  • Here are 2 shots of pftop.  Traffic graphs WAN out are off by 10 Kbps  Bridge shows 10 Kbps more than the WAN interface of the firewall.

  • I suggest using 1.2.1 for all bridging, 1.2 had some bridging related bugs that could cause strange behavior with what you're trying to do.

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