Objectives
This article explains how and why to set the Default Gateway for a CP1L-E PLC.
Introduction
Often, a PLC will need to communicate with devices beyond its IP network segment. The CP1L-E's built-in Ethernet settings must be configured properly to allow communications within its network segment as well as externally when a router is present. If a CP1L-E must communicate to devices that are not on its own IP network segment, settings must be made that facilitate the proper routing of messages.
Content
There is no "default gateway" selection for the built-in Ethernet. Instead, find this setting area in the Built-in Ethernet tab under IP Router Table in the PLC Settings area.
The IP Router Table provides a simple way to route messages to and from the PLC between different network segments. In other words, an IP Router Table is a table of correspondences for finding IP addresses for the IP routers that relay target segments when the PLC communicates via IP routers with nodes on other IP network segments. A diagram illustrates this below:
Make settings in the IP Router Table when the CP1L-E must communicate to an external IP network segment through a router.
The IP Router Table can accept up to 8 entries. One entry can be specified as default. Other non-default entries require information for external IP Addresses and the router's IP Address in which to use to access them.
Default Setting
This default setting is made when the IP Address is set at 0.0.0.0. All communications to IP addressed devices not on the PLC's network segment will use the router's IP address to access that network. The Router's IP Address value serves as a default gateway. Set the IP Address and Router's IP Address accordingly by clicking the Ins button shown below.
Non-Default Setting
When an IP address other than 0.0.0.0 is set, the PLC will use the specified Router's IP Address to access the device with the entered IP Address. In this way, the PLC will know how to access specific IP addresses outside of its network segment (different network ID). This is commonly used when multiple routers are present and/or different network segments exist. The following example provides a scenario when a non-default setting can be used.
Set the IP Address and Router's IP Address accordingly for Node A shown above. This will allow Node A to reach Node B with an IP Address of 130.26.1.1.
Beware of incorrect settings within the IP Router Table. This can occur if an invalid IP address is set that is outside the range of allowable IP addresses based on the subnet mask setting. For example:
Allowable IP Address Router Table setting:
Incorrect IP Router Table setting:
Auxiliary Relay A46.04 indicates the presence of an IP Router Table Error (ON if the IP router table information is incorrect).
Summary
Use the Built-in Ethernet tab found in the PLC Settings area to configure the CP1L-E for default gateway requirements. Several configurations are available so an understanding of the connected network is required.
References
More information about IP Router Tables can be found in the attached manual Sysmac CS and CJ Series Ethernet Units Construction of Networks Operation Manual (Cat. No. W420).
More information about the CP1L-E Ethernet setup and configuration can be found in the attached manual Sysmac CP Series CP1L-EL/EM CPU Unit Operation Manual (Cat. No. W516).
*These details and references were made in January of 2014. Later versions may operate and function differently. Contact your local Omron representative for more information.
