DHCP with Contrologix and Point IO

Doing a small side job with a Contrologix,Stratix 6000 managed switch and some point IO on Ethernet IP

Customer wants the plc to have static Ip Address and give DHCP to the 2 panelviews and the point IO modules.

The equipment is setup to do this but my question is lease renewal. How can I make it renew on powerup or something and not just based on time. I don't want it to renew while the machine is running.

Is this a concern or am i worried about nothing.

Customer wants DHCP because he has 2 other like machines that have this with siemens profinet I am told.

Seriously? They want PointIO on DHCP?

What are they going to do when it doesn't reconnect to expected IP address? And, does the PointIO have control associated, or just monitoring?

Well the point IO has DHCP options so there must be some way for it to work. I always thought it was to set initial addresses then make them static.

I have never used it. I like static and it soes not take much time to do.

We do DHCP per port on some stratix switches so if you plug a new drive into that cable it will get a dhcp addressbut it will be the same as the old drive.

These guys just want to do regular DHCP like you would with workstations in a office enviroment and I was not sure you could do it like that which is why I am asking.

Thats what they want. BTW their IT guy is in on this pretty tight too so that may be where it originated from.

It will be for control.

Short answer is tell them they are crazy.

For a control system, you want the ports on both sides configured the same ... static IP address, speed and duplex. Especially if you are doing control with the IO.

And ... the Control System LAN should be isolated from the administrative LAN.

I have to ask because I have never setup DHCP. How does the processor know what the address us for the I/O if the address changes? The only way I could see this working is if you do IP assignment by port which is what I think you hit on inthe above post.

If it where like an office network where it is first cone first serve than I see problems up ahead. Maybe Ken Roach will chime in and teach me a thing or 2

I haven't actually done this, so I don't know how it works.

When you configure an I/O adapter in RSLogix 5000 you can enter an IP address or a Host Name.

The way I assume it works (hey, there's that word again) is that when the ControlLogix needs to establish an I/O connection to that adapter (after powerup, or after a connection failure) it queries the DNS Server for the Host Name, then makes the connection to the IP address that the DNS Server tells it.

That's my guess, because frankly I'm not familiar with the low-level workings of hostname lookup in this context. I know how it works with my Windows computer, but not really with ControlLogix.

My concern for a system like this is that you've introduced another configuration that has to be done right before the system will work. Even if you use the DHCP Server inside the Stratix switch (and I'm not certain it includes DNS services) you're using either the web interface or the Cisco Network Assistant to set it up, and you would have to use one of those to add a replacement POINT adapter to the system. If the switch doesn't provide that service, now you're looking for a Server computer somewhere on the network to provide it.

In general, I recommend Static IP addresses for controllers and I/O devices because they're simple to set and can be replaced or repaired relatively easily.

There might be a reason for DHCP and Host Names to be used in this system, but so far I haven't heard anything except "IT wants it that way", which might be enough in the OP's context.

Just FYI with Schneider systems DHCP can be used very successfully. The Unity based PLCs all have DHCP servers built in, and all the ethernet devices (drives, remote io, etc) have a simple method of setting a role name (rotary switches, hmi panels). So then the plc will then issue an IP address based on the role name.
This means changing an ethernet device only involves setting a rotary switch (or a name on a hmi) and then you are back in action - no programming or configuration required.

So I am guessing OP has seen something like this