What Is the Common Practice Assigning IP Addresses to Remote Ethernet I/O Modules?

We recently had a member of our LinkedIn group ask other followers a question about assigning IP addresses to remote Ethernet I/O modules. The comment generated some great discussion by other members, who provided helpful suggestions.

Our group member wrote: "What is the common practice assigning IP addresses to remote Ethernet I/O modules? I considered the following options: DHCP or manual programming I/O with required IP before installation. Any other options?"

Kevin Pierce, electrical design engineer at Donaldson Company, replied: "Many engineers have their reasons for setting up their communications. Our standard for our business is to use Allen Bradley equipment. I currently am using the A-B 1734 point I/O along with the 1734-AENT(R) communication module(s). I prefer to use the 192.168.1.# static address scheme for the I/O network system for each main control processor. I utilize the three-digit manual address selector on the AENT card. This is good when the AENT card fails and another one is used to replace the bad one. The maintenance person or engineer only needs to set the three-digit address and the system is up and running again. As far as any drive located in a field termination box, a HIM with the copycat feature is used to back up the parameters so they can be restored to a drive that needs to be replaced. Also, I use either a Cisco 2955 or Stratix-managed switch with IGMP snooping turned on, and let the switch manage the traffic"

Christopher Brunner, owner of Brunner Equipment, also replied: "The two choices you have are either dynamic or static (e.g. DHCP or manual). I prefer to use static addressing on my networks as it allows me to know every address of each sensor. It requires more recordkeeping and a higher level of self control when doing installations and maintenance (the "stick it anywhere" can cause conflicts). DHCP on the other hand works fine if you have a higher level of communication running on the same network – a management software that allows you to walk the network without needing to know IP addresses. Where things start to really get interesting is when you're doing multiple network segments using a third party in the middle to do data transmission (e.g. local telco or internet provider)."

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