Dynamic Host Configuration Protocol (DHCP)
In today’s world, just about every device we own is somehow able to connect to the internet, or at the very least is able to be part of a network. When you walk into your house, your phone, tablets, and laptops automatically connect to your WiFi without having to set an IP address; that automatic connection is DHCP at work. Without DHCP, you would have to manually set the IP address of every device that you would want to be connected to your network. A process very similar to configuring your PLC, Powerflex or Kinetix drives.
A DHCP server has a pool of IP addresses that the server can “assign” to a DHCP client. The process is quite simple:
- A DHCP enabled Client (Poweflex drives, Logix PLCs) sends a signal requesting an IP address
- The DHCP Server receives the request and leases out an available IP address from the pool
- The DHCP Client receives the leased IP address and sends an acceptance signal back to the server
- The DHCP Client is now connected on the network.
While this process is incredibly useful in commercial settings, this doesn’t particularly help us in the world of industrial automation.
What DHP Means for Industrial Users
Dynamic Host Configuration Protocol, DHCP, is another way to improve efficiency. We care very much about improving the efficiency of the plant overall. There are two more specific ways to look at efficiency: (1) the amount of time and effort it takes Engineering and IT to set up networks and connect equipment properly, and (2) the amount of time and effort plus average chance of failure involved with ongoing plant floor maintenance.
When you are designing and building machinery, you will need to integrate componentry into networks and there are a variety of ways to set a network IP address. You could:
- Use RSLinx software
- Use another programming software
- Use DHCP
Which of these is most efficient? It depends. Designers have some variables to consider when making this decision:
- How isolated or integrated is this network?
- How large is this network?
- What are the required and relevant IT and company policies and procedures for this plant floor network?
Let’s consider isolated networks and/or large networks. It can be more convenient and efficient to use DHCP server rather than the programming software or RSLinx software. This, typically, can result in a more efficient installation. But that is just start up. Maintenance may be tougher since the devices will have an IP address from a pool of addresses.
CPwE and DHP
You should be aware of the Converged Plantwide Ethernet (CPwE) Design and Implementation Guide. Found here. This is a 500+ page PDF file, approx 20 MB in size. This document gives recommendations for using both DHCP and statically addressing IP addresses. While DHCP can be more efficient on start up, there are considerations for troubleshooting and maintenance and security. Using a mix of DHCP persistence and statically setting an IP address is typically a best practice and often our recommendation.
Having static IP addresses for your PLC, drives, and other Ethernet-enabled devices is critical for communications and operations. For example, when you create a Logix Program, your drives must have an IP address that the PLC can send messages to; if we were to use DHCP, the IP addresses of the drives would be different every time and therefore the PLC and drives would not communicate with one another. However, by using DHCP Persistence in a Stratix 5700 switch, this issue can be resolved.
It’s Good To Be Persistent
DHCP Persistence is a process in which you statically assign an IP address to a port on a switch. For example, Port 4 will be assigned an IP address of 192.168.1.54 with DHCP Persistence. Any DHCP enabled device that is connected to Port 4 will receive an IP address of 192.168.1.54. When used in congruence with ADC (Automatic Device Configuration) enabled devices such as an IO-Link Master or PowerFlex drives, a true “plug and play” environment can be created.
Remember, DHCP is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway. For more information please contact your local automation specialist.
How do you assign IP addresses? How long does it take you? What are your best practices?