The 2.5 network is between the external Network Interface Card (NIC) and the firewall or other security or network device separating the DeltaV system from any external network. The 2.5 designation refers to the ISA S95 architecture model where the control system is designated as level 2 and the level above the control system as level 3. Level 3 is typically a process information network or a DMZ (demilitarized zone).
The 2.5 network is not shared with other systems and communications that are not specifically targeted to DeltaV workstations are not allowed on this network. Only network traffic from the DeltaV workstations' third Network Interface Cards (NICs) are allowed on this network. It is expected that the 2.5 network is segmented from non DeltaV traffic by a firewall or router properly configured to allow only DeltaV inbound and outbound communications.
