Dual IP address for 1734-AENT/B Point IO

[Muro]

Hello. My facility has Point IO modules (on a separate cabinet) which is connected to a controllogix PLC via 1756-EN2T module. We lost communication with all of the Point IO modules. Going to the cabinets which houses point IO modules doesn’t help because there are no warning lights. All the indicating lights should results in good status according to Allen Bradley document. I went directly with laptop to the 1734-AENT/B Point IO module. I couldn’t ping the IP addresses (each 1734-AENT/B module has two ip addresses. Using Bootp didn’t help, so I used browser to set the first IP address. I don’t know how to set the second ip address. Going online with the controllogix controller (after setting the first ip address) didn’t help as Logix5000 program doesn’t recognize the module (which ip address was set).

Does anyone know why they would set two ip addresses for a single 1734-AENT/B Point IO module, and how I can set them?

 

[Ken Roach]

Welcome to the PLCTalk forum community !

The 1734-AENTR has an embedded "Device-Level Ring" port, allowing users to daisy-chain Ethernet connections and/or create a single-fault-tolerant ring network if all the involved devices support DLR.

They definitely only have one IP address.

Does your system use ControlLogix Redundancy, which would make the pair of redundant CPU's control pairs of 1756-EN2TR modules with adjacent addresses ? Maybe there are CompactLogix 5069 controllers in your system, which have the option to be set up with dual IP or with DLR ring ? Those are the main places in an A-B control system I can think of where one device or assembly would have two IP addresses.

It sounds like there may be some routers, NAT devices, or mis-labeling in your system.

 

[Muro]

Thank you for the warm welcome Ken.

The Controllogix L73 system doesn't use redundancy, which is why it is surprising why they configured a single ethernet port (no redundancy) 1734-AENT/B module with dual ip addresses. This thing was working for a year. 1734-AENT/B point IO modules are routed to an NTRON switch. I've tried rebooted the NTRON switch as well as Ethernet IP module (next to Controllogix processor).

 

[Ken Roach]

Thank you for confirming that it's an ordinary 1734-AENT Series B adapter, with just one RJ485 port.

The POINT adapter definitely has only one MAC ID, and only one IP address.

If there is a label in the cabinet indicating otherwise, then you need to figure out who printed it and what it actually indicates.

My best guess for the reason there are two addresses labeled for the adapter there is that there is a "Network Address Translation" (NAT) device or a bridge somewhere that provides an enterprise network address and forwards all the traffic to the 1734-AENT. That would be common for a ControlLogix, but not for a POINT I/O adapter. It's a puzzle.

The 1734-AENT has a three-digit pushwheel selector on it. When that shows a value between 1 and 254, then the module uses an IPv4 address of 192.168.1.X. If the number is anything but that range (or 888, which performs a factory default) then the IP address is set in software (almost always using RSLinx Classic) or derived from BOOTP/DHCP, and those settings are saved in NVRAM. This is concisely described on pages 9 and 10 of the Installation Instructions.

My overall guess is that someone set this adapter to DHCP at some time in the past, and it didn't take effect until months later when there was a power cycle.

To troubleshoot it, I would connect just my PC and the 1734-AENT, and run Wireshark and the BOOTP/DHCP Server utility on my computer until I saw either some announcement traffic showings its IP address, or a DHCP Request from the adapter.

Or, set it to defaults with the pushwheel switch and just configure it from scratch.