NE871 is an industrial router that also acts as a firewall. The router/firewall can be utilized to segment a system into network areas and also security zones. NE871 is primarily intended to connect a client-server network to a plant network or to a DMZ (demilitarized zone).
The concept of security zoning is described in IEC 62443. In short, security zoning is a method to segment a system into zones with different security levels. A security level is complied with by implementing a combination of security countermeasures. The reason why it potentially could make sense to divide a system into security zones, which comply with different security levels, could be that the risk for different parts of the system varies. Another could be that the impact of a potential incident varies.
NE871 supports RNRP (Redundant Network Routing Protocol), which enables 800xA to have two physically separate networks, and thereby avoid a single point of failure.