Safety Network Number

The safety network number (SNN) uniquely identifies
CIP Safety™
 subnets within a routable safety network. The combination of the SNN + Node Address uniquely identifies each CIP Safety port on each device in the routable safety network. Safety controllers require two SNNs:
  • An SNN for the backplane
  • An SNN for the Ethernet port
Safety Network Numbers
Example safety network number for a safety controller

Safety Network Number Assignment

When you create controller projects, the
Studio 5000 Logix Designer®
 application generates an SNN value automatically whenever it recognizes a new subnet that contains
CIP Safety™
 devices:
  • Each
    CIP Safety™
    -capable port on the controller is assigned an SNN. The
    GuardLogix®
     5580 controllers have two safety network numbers: one for the Ethernet port, and one for the backplane.
  • If a bridge or adapter device is in the I/O tree and a child
    CIP Safety™
     device is added, the subnet that is created by the bridge or adapter is assigned an SNN.
For typical users, the automatic assignment of a time-based SNN is sufficient. However, manual assignment of the SNN is required if the following is true:
  • One or more controller ports are on a
    CIP Safety™
     subnet that already has an established SNN.
  • A safety project is copied to another hardware installation within the same routable
    CIP Safety™
     system.
We recommend changing each SNN to the SNN already established for that subnet, if one exists. That way, devices created later in the project are automatically assigned the correct SNN.
For information regarding whether the controller or Ethernet ports are being added to existing subnets, see the GuardLogix 5580 and Compact GuardLogix 5380 Safety Reference Manual, publication 1756-RM012.
Each safety network must have a unique safety network number. You must be sure that a unique SNN is assigned to each CIP Safety network that contains safety devices.
TIP:
Multiple safety network numbers can be assigned to a
CIP Safety™
 subnet or a
ControlBus™
 chassis that contains multiple safety devices. However, for simplicity, we recommend that each
CIP Safety™
 subnet has only one unique SNN.
The SNN can be software-assigned (time-based) or user-assigned (manual).
For more information on time-based assignment, see Automatic Assignment of Time-based Safety Network Number. For more information on manual assignment, see Manual Assignment of Safety Network Number.
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