Hello, In my setup, I have 3 LM devices version 20240426, all connected via TP on three separate branches that are not interconnected. I am using them as BACnet Servers, but I also need them to function as IP Routers to exchange group addresses between them.
I tried configuring the 3 LMs as IP Routers, as shown in the image, setting the same Multicast address. Sometimes the first two work, but after a few minutes, they stop functioning. What could be the issue?
Hi Daniel,
they are on the same subnet. The customer has other equipment, but it is not on the same VLAN. I changed the address because this system we have 14 LMs, and I want only a few of them to communicate with each other. For example:
• LM1, LM2, and LM3 use multicast address 1
• LM4, LM5, and LM6 use multicast address 2, and so on.
I have the same problem, communication works but stops after a few days. A reboot of the LM every night circumvents the problem. But I am still looking for the cause. From openrb it refers to the network equipment of Mikrotik and Ubiquity. And from them it refers to the LM
(23.12.2024, 22:16)Erwin van der Zwart Wrote: We see often that multicast is blocked by managed switches, ask IT to check this..
Hello Erwin, The LMs function for a few minutes but then stop working until they are rebooted, exactly as gjniewenhuijse described. I believe that if multicast communication were completely blocked, they wouldn’t work at all, correct?
As Erwin said, IGMP must be configured properly in your network if you have L3 switches.
KNX/IP uses multicast messages which by default are forwarded to all devices on the network. IGMP is used to limit multicast exchange only to hosts that require these messages.
When LM starts it will send IGMP group membership report to allow switch/router to forward KNX/IP multicast messages. Then the switch/router is responsible for sending membership queries to ensure that LM or any other device is still operational and is a member of a certain multicast group.
