Why should the BROADCAST gateway be avoided in KNX?

Communication with KNX devices and their data points is done via KNX group addresses. Since our server products are using IP as standard interface to the field/automation network, each KNX group address has to be assigned to a KNXnet/IP router or interface.

Within the server, the so called BROADCAST gateway is available. Please keep in mind that BROADCAST is NOT the same as KNXnet/IP routing. BROADCAST means “all KNXnet/IP routers and interfaces together”. Therefore, the BROADCAST shall only be used in rare, special cases. The reason is that, if you are sending a telegram to a KNX group address that is assigned to BROADCAST, the server is sending a group telegram to EACH gateway. If you have 50 gateways it will send 50 telegrams – one to each router. Since KNXnet/IP routers are also forwarding telegrams between their lines (based on filtering), you will have a lot of traffic there.

Therefore, BROADCAST should only be used in rare, special cases. For example:

• if you have only one (1) KNXnet/IP router or interface
• if only KNXnet/IP interfaces and no KNXnet/IP routers, line or backbone couplers are used
• if you are using KNXnet/IP routers but all routers have KNXnet/IP routing deactivated (no routing between KNX lines).
• for central commands that configured within the ETS

Article applies to the following products:

• NETx BMS Platform
• NETx Multi Protocol Server
• NETx BMS Server 2.0