9/15/2023 0 Comments Wireshark mac addresses![]() ![]() The maximum number of MS/TP masters in a BACnet network is 128 with the highest MAC address at 127 (decimal). In our example only station 06 has a gap in addresses between it and its logical neighbor being station 00 so it must periodically initiate a PFM. This process is called Poll for Master (PFM)). If address gaps exist between one station and the next higher station, the lower station is required to periodically check if a new station within the gap wants to join the network. What we learn from this is that we have a stable network with a total of seven stations. Station 01 passes the token to station 02 and cycle continues with the last station 06 passing the token back to the BASrouterLX. From here you can learn that station 00 (the BASrouterLX) is passing the token to station 01. What is shown is a simple token pass with no stations initiating messages or responding to messages. Next are the protocol that is discovered and some information on the type of frame. Next is the source address in hexadecimal followed by the destination address. The left-most column of a PCAP file is the frame number followed by date and time stamp. What follows is a sample of the type of data you may see. Scroll through the lines of captured data for points of interest. Once the web browser data transfer ceases, click the View MS/TP Traffic button which opens up the Wireshark program with the transferred file. By clicking on the Generate button, the BASrouterLX simply dumps the most recently captured MS/TP data into a Wireshark PCAP file. The BASrouterLX is always recording MS/TP traffic using a 3900 line ring buffer. There are two buttons - Generate MS/TP Traffic Wireshark File and View MS/TP Traffic. Go to the Status tab and select MS/TP Traffic. If you want time-stamped events recorded, make sure the time is set correctly on the BASrouterLX. In the examples to follow, the BASrouterLX assumed the station address 00. From the Setup tab on the BASrouterLX, jot down the MS/TP MAC address of the router which will help you when examining the Wireshark PCAP captures. Using your web browser, access the web server on the BASrouterLX attached to the misbehaving MS/TP segment. Wireshark, with a built-in BACnet decoder, can be downloaded for free from the Wireshark website. All you need is a copy of Wireshark® loaded on your laptop computer. ![]() This could even be done over the Internet. In addition to handling BACnet MS/TP to BACnet/IP routing, the BASrouterLX allows you to peek at the MS/TP side of the router from the convenience of a spare Ethernet port on your BACnet/IP network. A less intrusive approach is to use the built-in diagnostic features in Contemporary Controls' high-performance BACnet® router. Connecting to a functioning MS/TP network means you need to disturb the communications wiring just to attach your serial protocol tool. With many devices attached to a single MS/TP twisted-pair wiring bus buried in a false ceiling, you want to be very sure what MS/TP device you need to examine before making the climb to the device. Troubleshooting a BACnet MS/TP network in the field could be quite a chore. Make Life Easier when Troubleshooting MS/TP Networks ![]()
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