Helmholz 700-875-LTE11, 700-875-LTE61 REX 100 Router User Guide

9 Remote maintenance of Ethernet CPUs  

The LAN ports are suitable for 100 Mbps and full duplex operation and support auto- crossover and  

auto-negotiation. No special PROFINET functions are supported. When connecting additional  

Ethernet participants (PLC/panel) on the REX 100, it must be ensured that the IP addresses of the  

devices lie within the address range of the LAN interface of the REX 100.  

9.1 Device settings: Services – Firewall – SNAT  

With a REX 100, the SNAT function is activated as a default. With this setting, participants for which no  

gateway*/router has been entered are accessed via the VPN tunnel. For the CPUs and panels of some  

manufacturers, it can be the case that you need to explicitly enter the gateway* and deactivate the SNAT  

function in order that a remote connection with the end device is possible.  

*Gateway: This refers to the configured LAN IP address of the REX 100.  

To access a PLC or panel via the VPN tunnel, the OpenVPN adapter must be selected in the correspond-  

ing engineering tool as the interface. The virtual network connection responsible for this is the TAP  

Windows Adapter V9.  

The excerpt shown here shows the setting to be selected in the PG / PC interface module from the SIMAT-  

IC STEP 7/TIA software.  

9.2 Search over IP  

With the SEARCHoverIP function activated, unparameterized network components (PLCs with IP ad-  

dress: 0.0.0.0) can be found and configured remotely. However, this search function is not supported by  

all control manufacturers!  

When SEARCHoverIP is activated, the "remote maintenance network" (remote client) is connected  

one-to-one with the LAN network on the device (router) via Layer2. These broadcasts and multicasts  

on the remote maintenance side generate additional data traffic through the VPN tunnel. Under  

certain circumstances this can lead to IP address conflicts and network disruptions on the router LAN  

side. It is therefore recommended to deactivate this function in normal remote maintenance mode!  

In the delivery state, SEARCHoverIP is not activated.  

QuickStart Guide REX 100 | Version 14 | 22.01.2025  

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