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aarondcounts 12-11-2009 04:00 PM

Linux based filtering tap for IDS
I am looking for help on building a Linux based filtering tap for my IDS implementation. I would love to purchase a hardware driven filtering tap but they are too expensive so I know want to try and build a Linux box that can do the same thing.

The idea is to have a network tap or span port connected to the server and then the server will filter and/or redirect the mirrored traffic to the appropriate tool. This will help me control what tools see what traffic.

The traffic from user 1 would be forwarded out the interfaces connected to tool1 and tool3. User2 would be forwarded to tool2, user3 would be forwarded to tool3 and user4's traffic would just be dropped. The interfaces on the tool servers would be configured to listen only would not do any routing of traffic back to the users, this is strictly to copy the data and pass it to my tools.

Here is the basic idea in test/image form

User1 User4 User2 User3
| | | |
| | | |
| | | |
--------Corporate Switch---------
| |
| Linux Filtering
| | | |
Router Tool1 Tool2 Tool3
User1 User2 User 1 &

rweaver 12-11-2009 04:11 PM

I don't see any particular reason why this couldn't be accomplished with iptables and a decent router. That being said you've not really asked any specific question that someone can answer other than "is it possible?"

OlRoy 12-13-2009 07:08 AM

I'd check out DaemonLogger, and maybe Linux Interface Bonding and other pages on that site. The problem with not purchasing a tap is that you will add a single point of failure if your monitoring box is inline. Real taps will continue to pass traffic even if they aren't powered on.

aarondcounts 12-14-2009 02:54 PM

The idea is to use a tap to mirror the data to the Linux server. Then the Linux server would use iptables to filter the traffic and forward it out additional interfaces to the appropriate servers that are connected via cross-over cables. The IDS servers will then have a promiscuous port to listen to the traffic. What would an example config be for this type of configuration on the Linux server? I currently do not have a config started.

aarondcounts 12-16-2009 12:37 PM

can someone help me with this exact command?

forward source interface (eth5) source address/network ( to destination interface (eth3) so that the traffic will be forwarded to my IDS server directly connected to eth3 via crossover

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