TAP Devices, Siemens TAP 104

Few months ago, I wrote about how port mirroring is an allied to capture and analyze network traffic. You can access to the article clicking here. There are a lot of reasons to use it, such as identify communications, troubleshooting tasks, use of IDS/IPS systems, and so on. But port mirroring is not the only one, we can use TAP devices. However, as I said several times, we must use specialized equipment for these environments, in particular industrial ones. Today I will talk about Siemens TAP 104.

Siemens TAP 104 is a hardware device that can be installed between two devices to gather a copy of data traffic on Ethernet based networks. Once the collected frames are stored, we can visualize them with a network analyzer tool to identify the information that we are looking for. The TAP device does not affect to the communication that pass through it.

Siemens TAP 104

It has four RJ-45 ports. Two to connect the segments that we want to monitor and two more to connect the systems to collect the frames. It operates in a fault-free mode even when the power is off.

One use case can be as the picture below shows. For example, we can be interested to identify issues between the HMI and the S7-1500 PLC. The traffic will be gathered by Grassmarlin tool that can be downloaded from here. I wrote about it more than a year and half. You can find the article clicking here.

Siemens TAP 104

Following the concept of the previous picture, this time, I have replicated this scenario in small testbed. In the picture below you can identify different devices, such as Fortinet Fortigate Rugged 90D, Fortinet Fortiswitch 112D-PoE, Siemens PLC S7-1200, Siemens HMI, Siemens TAP 104 and a laptop. As you can see, the TAP is just in the middle of the Fortigate switch and the PLC. Each communication from and to them, is replicated to the first RJ-45 port, where the laptop is connected and running Wireshark packet analyzer.

Testbed Lab

Testbed Lab

Once the traffic is gathered, we can open it with an analyzrer. Below we can see the information available from LLDP protocol as system description, IP management address, and so on.

LLDP Wireshark

But if we are looking for information, we can see the values of sending and receiving from and to the devices.  In the picture below you can see the field “Function: GetMultiVariables”

S7 Communication Wireshark

And then displaying the field “Response Set-ValueList”  we can see the values 84 and 16, the same that appears in the HMI.

S7 Communication Wireshark

Today, with Siemens TAP 104, we see other way to gather network traffic to identify possible issues in our industrial communications where it is mandatory not to introduce additional latencies that may affect them. In general, it is very common to do it using Port Mirroring configurations, but as we have seen, there are others. Either Port Mirroring or TAP devices, we can find them a helpful resource for different use cases such as troubleshooting, anomalies, security problems and much more. Always with specialized equipment.

That is all for now, see you next time!

Edorta