Thursday, September 09, 2010

DualComm Port Mirroring Switch

John He from DualComm Technology was kind enough to send me one of his company's port-mirroring switches, namely the DCGS-2005 pictured with its box at left.

In the figure, I have port 1 going to a computer I want to monitor. Port 2 is going to the uplink (or access switch) for that computer. Port 5 (at the far right) is going to a sensor.

The idea behind this device is to provide a plug-and-play alternative to network taps. I thought this system was interesting because it acts somewhat like a port aggregating tap, in the sense that two ports are used for accessing the network but only one port is needed by the sensor.

Note that only port 1 is mirrored to port 5. (The manual confirms this, and I did some limited testing. The words on the tap imply ports 1 - 4 are all mirrored.) This is a one-for-one copy. If you connect to ports 2 and 3, 2 and 4, or 3 and 4, you will not see any unicast traffic on port 5.

This device is also different in that in requires a USB connection for power.

Probably the biggest advantages of this device include low cost and simple use. I think the single USB power connection is the biggest disadvantage. I'd also like to know more about the software on the switch itself.

Thanks again to John for sending me this device. Check out DualComm for more information!

5 comments:

Dave Crawford said...

For monitoring my various home networks I use a Netgear GS108T (you can grab a version 1 of the device at various online stores for $89).

I configure ports 1 & 2 to VLAN2, ports 3 & 4 to VLAN3, port 5 is a mirror for ports 1 and 3, (bi-directional) and the remaining ports are left on the default VLAN and act as a normal switch.

I then loop the networks I wish to monitor through ports 1+2 and 3+4. Then on my monitoring device (connected to port 5) I create virtual interfaces and route traffic to them from the physical interface based on the VLAN tag in the Ethernet frame.

This allows me to easily run multiple instances of SGUIL on a single server, e.g. one watching internal traffic, the other watching honeypot traffic.

Andrew said...

Richard, the correct URL for DualComm is: http://www.dual-comm.com/ whereas the URL provided at the end of the article is a domain parking lot.

Richard Bejtlich said...

Thanks for everyone who pointed out the incorrect URL!

Tom said...

Amer makes a switch that does multiple port mirrors and has combo ports.

We use this to do 4 port mirrors on a single device.

http://www.amer.com/_e/Managed/product/SS2GD8i/Amer_com_Managed_6_Port_1000Mbps_plus_2_combo_Copper_SFP_port_switch_SS2GD8i_.htm

Morgan Storey said...

I can see the USB powered bit being useful, if you are red team you can hide it inside a tower plugged into either internal or external USB. If you are using for analysis at different points on the network there will usually be a server or workstation nearby that you can get the power off, not having to worry about using up another power point.