Configuring an A-B CompactLogix L16ER as a DHCP server

I'm working on a project where I need a wireless modem to receive an IP address from a DHCP server.

The network consists of an HMS Anybus Wireless Bolt modem, connected to an A-B CompactLogix L16ER.
This system needs to be able to connect to other Anybus modems with a static configuration on various subnets.

Since I only have the CompactLogix hooked up to the Anybus modem, I wanted to see if I can use the PLC as a DHCP server
to dole out different IP addresses to the dynamically configured modem.
The IP address dealt to the modem will vary, based on which of the statically configured modems it needs to link to.
The communication route will be set manually by a switch in the system.

I wanted to check if anyone had tried this out, or had a similar problem at hand before I dove into it myself.

You're going to need an external device to act as a DHCP server, the PLC is only a DHCP client. Even the cheapest of routers can do this for you.

Thanks bjh,

The problem with using a router as a DHCP server for the Anybus modem is that it would need to know which subnet to switch it to.
I'm guessing this could be quite difficult to accomplish, although not impossible.
This information lies in the PLC and is the reason I'm interested in using it as the DHCP server.

My description of the problem is pretty vague, so I hope this diagram helps explain it better:

Hmm, You would have to check w/ Anybus, but can the Rs-232 pins on the device be setup to accept serial AT commands? I know that device will take AT commands over telnet already..

If it can, You could add a 1734-232 module and use serial AT command to change the IP setting and then issue a reset to the bolt.

Good point Dravik, I knew of the AT telnet commands but hadn't thought of the possibility that maybe they could be issued via serial.
I was hoping to find an easier solution but this might just be necessary.

I'm guessing I could also use the bluetooth functionality of the Anybus, which in fact I didn't know of prior to posting this topic.
If the bluetooth range is OK, it might be a feasible alternative to WLAN if, and in that case I won't have to deal with IP address assignment.

You *could* also use the socket commands in the CompactLogix to issue the telnet commands, but that's going to be even less easy I suspect

I've actually had some experience with socket commands in A-B, as I've had to establish communication between A-B and Siemens processors.
Not that bad once you get your head around it. We'll see how it goes...

This device is new to me. Sorry for the stupid questions:

1. Are you using wifi mode, or one of the others?
2. Is one device an access point and the other clients?
3. Are they all connected at the same time?
4. From the spec sheet:

Supports wireless bridging of Industrial Ethernet protocols: BACnet/IP, EtherNet/IP, Modbus-TCP, PROFINET

Do you need to put an IP on the actual Bolt device configured for the various networks? Usually when I see multiple subnets, I think router. You see physical switch and changing IP address to be in same layer-2 domain. It's OK, just a different view. The typical enterprise network solution to something like this is using separate VLANs for each subnet, and having a separate SSID for each VLAN. A router would then be used to allow communication between the various subnets (inter-vlan routing).

Anyway, looks like an interesting device, especially if it bridges WiFi. I think I may need to get one.

Hey Rob. I think I've figured out how I'm going to work around this.

As a brief introduction, the three different subnets are based in three factories. The thing is that two are actually very, very close to one another. My system is portable and should be able to travel between the three sites and connect to devices there.

Here goes:

1) I will be using the WiFi mode.
2)The WiFi mode allows for configuration of AP's and clients.
A client can be set to connect by default to a specific SSID. I will configure the wireless modems of the 3 different subnets as AP's and give all of them the same SSID. This will be OK since their ranges are unlikely to intersect.
I will set my system as a client which pairs automatically with the given SSID.
3) We can look at these devices as not being connected all at the same time, given that the range of the two troublemaking AP's won't intersect.
4) It seems I don't need to set an IP for the Bolt on the same subnet as the device, it just bridges the ethernet networks together.
I gave it a go earlier this evening, hooked my CPLX to the Bolt client and an SLC I found laying around to an AP Bolt.
I was sending ethernet messages between the two in a matter of minutes.
I then used the logic in the CPLX to change to another IP address, configured a new address for the SLC manually, and it came straight back up.

It just kind of works...

I, too, think you may have to get one.

Disclaimer: never used sockets in Logix, only CIP/SLC read/write

That being said, I understand that the L16ER has socket services, and that you can do UDP sockets with it. Again, never used sockets so I don't know if there's a limitation I'm not seeing, but just the fact that it can do UDP sockets, I'd think that you could implement a DHCP server in your program. Looking at the protocol itself here: https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol#Operation not terrible.