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When TIA Portal can’t find the PLC, or the HMI can’t connect, the cause is very often the IP settings: the devices are in different subnets, or two devices share the same IP. Enter every device on the machine network to see who can talk to whom.

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How subnets work

An IP address has a network part and a host part. The subnet mask decides where the split is:
  • 255.255.255.0 (/24): the first three numbers are the network. 192.168.0.1 and 192.168.0.2 are in the same network, 192.168.1.10 is not.
  • 255.255.0.0 (/16): the first two numbers are the network, so 192.168.0.1 and 192.168.1.10 are in the same network.
Two devices can talk directly (without a router) only when each one sees the other inside its own network. The first address of a network (the network address) and the last (the broadcast address) can’t be given to a device.
This checker looks at direct connections on one Ethernet network. Devices in different subnets can still talk through a router or gateway, which this tool doesn’t model. PROFINET device names, VLANs and firewalls can also block a connection.

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