Safety Network Numbers (SNNs)

Communication within a control system travels over subnets that are interconnected with bridging or routing components. The following are examples of subnets:
  • The backplane of a chassis
  • A bank of I/O modules
  • An Ethernet subnet within a LAN
Rather than creating a UNID directly for each
CIP Safety
device, which can be prone to error in a large system, each subnet has a unique safety network number (SNN), and the UNID is created from the SNN + the node address.
In Logix SIS, an SNN applies to an entire redundant chassis pair.
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