CompactLogix Ethernet Problem

[Jinto 0]

Hi, I had an issue with a compactlogix PLC last night and I could use a little advice if anybody has seen this before. I was asked to change the IP address of a 1769-l32e and local HMI which were set for a private network to settings which would allow connection to the factory network. The settings I was given to put in were IP 172.16.4.14 sunbet mask 255.255.240.0 gateway 172.16.255.254 After getting these settings in via linx and establishing comms ok with the HMI everything looked good, however after powercycling the machine the PLC lost it's CIP connection to the HMI and linx. I could still ping the IP address ok but could not connect and the NS light was solid red indicating a duplicate ip which was not the case. (even disconnecting the PLC from the network and rebooting it would cause the same conditions. The only way I could reconnect to the PLC was to run bootp and reset the IP address to what it was already set to. I was quite surprised to be able to see the boot p request because bootp and DHCP were both switched off in the PLC configuration. I eventually managed to stop this happening by removing the gateway address completely. Any suggestions guys?

[TimWilborne 108]

What was the original IP address, subnet, and gateway of the PLC and HMI?

[Jinto 0]

Hi, they were on a private network PLC 192.168.1.151 subnet 255.255.255.0 HMI 192.168.1.155 subnet 255.255.255.0 From what I've just been going through on the technical help files, it looks like the PLC is not happy that the gateway is a valid address. which I believe can cause it to have comms problems even though it worked happily until it was powered down.

[Gigabit 1]

The gateway address is wrong, or at least, wrong for this network. The subnet mask defines the network portion to be the first 8+8+4+0 = 20 bits from the left. The network part of the PLC address is hence 172.16.0, but the network part of the gateway is 172.16.240, that is, different networks. If you don't need the gateway, leave it out. If you do, the PLC has to be in the same network as it. I'm not confirming this is the cause of your problems, however you have seemed to indicate the gateway address is invalid for this PLC addresses, and you are correct.

[Jinto 0]

Thanks, yes you are right and it was the problem. When I realised that it seemed to be the gateway I had a closer look and realised that they must have given me a bad address as it was outside the subnet range. But the nature of the fault was odd as It let me put the new settings in while running and it was communicating fine with the hmi until the next power cycle. Then it lost all connections even those on the local subnet, not just connections over the gateway. And the duplicate IP address led was on which threw me for a while.

[TimWilborne 108]

I had to look it up but interesting you can change the IP address on the controller on the for but to change the subnet you do have to cycle power. So you were ringing on the old subnet and new IP is how I read it. See page 34. http://literature.rockwellautomation.com/idc/groups/literature/documents/qs/iasimp-qs023_-en-p.pdf