Routing
10.3 IP forwarding
Communication
Function Manual, 11/2019, A5E03735815-AH
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Requirements for using IP forwarding
● S7-1500 CPU as of firmware version V2.8
● Number of Ethernet interfaces:
– The CPU has at least two Ethernet interfaces.
– Or the CPU has one Ethernet interface, and a CP 1543-1 as of firmware version V2.2
provides the other Ethernet interface. In this case, the "Access to PLC via
communication module" function must be enabled for the CP in the CPU.
● IP forwarding is enabled.
● Suitable standard gateways/routes are configured in each participating device along the
outgoing and return paths of the IP packets.
IP route table
When IP forwarding is enabled, the CPU forwards received IP packets that are not
addressed to itself. How the CPU forwards the IP packets is defined in its internal IP route
table.
The CPU automatically creates the IP route table from the following information of the loaded
hardware configuration:
● IP configuration of the Ethernet interfaces
● Configured router
Example of a configuration with IP forwarding
The following figure shows a sample configuration along with the required IP address
settings and router settings.
● A PC on the IP subnet 192.168.4.0 communicates with an HMI device on the IP subnet
192.168.2.0.
● The IP address of a router ("Standard Gateway") is configured at the CPU, Ethernet
interface X3; in the figure below it is the device that is designated as "IP Router".
In STEP 7, you configure a router in the interface properties under "Ethernet Addresses"
> "IP Protocol".
Figure 10-7 Configuring the router
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