Wireshark disclosed that the 'studio' software on the PC was using multicast destination addresses (possibly L2 multicast, not necessarily 元 multicast, I don't remember anymore) and the packets to multicast destination did not pass through the switch (got dropped / filtered by the switch).įrom there, it turned out that the switch had IGMP snooping enabled (user configurable option of the switch management firmware) and apparently the Siemens Profinet devices do not run IGMP, so the switch did not know about any multicast recipients (who would've subscribed via IGMP), and therefore did not open any port to multicast traffic. Ping did work, Profinet IO payload sessions did work, but device detection in the 'studio' did not. Not sure if this was the TIA portal or some other Siemens PLC config software (of the Simatic stable), but once upon a time I've witnessed a problem where some such management software could not find the Profinet devices it was supposed to configure/manage. What does your layer 2 (Ethernet) network connectivity look like? Just a direct cable? (Does straight / crossover matter?) Or are you running this through a switch? If so, what sort? Dumb, or managed? If managed, does the switch know anything about IP multicasting = does it support IGMP Snooping?
