Assign a specific IP address to each switch port

Hello,

I am looking for cheap switch with functionality to assign a specific IP address to each switch port. I've got expensive MOXA EDS-510A already, which has an option called "Set Device IP" (http://www.moxa.com/product/eds-510a.htm).

I am looking for alternative, cheaper solution. It should assign IP address by DHCP to a device (PC or PLC), depend on physical port, e.g. port 1. - 192.168.0.1, port 2. - 192.168.0.2, etc.

I've got also Linksys WRT54GL. There are many versions of firmware and mods based on Linux (Tomato, OpenWRT, DD-WRT). I can be freely modified, so I suppose that it is possible to implement such functionality. But I'am not good enough at Linux nor networks.

Another idea I've googled is sth. with VLAN and trunking back options, which are implemented in some managed switches/routers, but I don't know how to set it up. Here you can read about:
http://www.keyongtech.com/4541374-assign-static-ip-to-each
Also smb. mentioned few words about DHCP Forwarding and Interface Tracking here: http://www.tomshardware.co.uk/forum/19995-17-assign-static-port-managed-switch.

Thanks in advance for help,
marcowy

marcowy - are you sure you want to do this ?

setting a device's IP address depending on which switch port it is plugged into, is, IMHO, asking for trouble.

dynamically asigning IP addresses generally falls into 2 categories...

DHCP - a server leases addresses to clients from a "pool" of adrresses. Works on the basis that they do not need to be set to specific addresses, but must just join the domain.

BOOTP - a server assigns addresses to clients based on their MAC Addresses, which are unique to the device. Each time a BOOTP enabled device joins the network, it will be given the same addresses.

for plc systems, however, my preferred method is to have static addressing, using absolutely FIXED IP addresses, especially if you have inter-plc or SCADA/HMI communications taking place. BOOTP will let you down if you have to replace the Ethernet processor or comms card, since the new MAC address will not be recognised by the BOOTP relation list.

Originally posted by daba:

BOOTP will let you down if you have to replace the Ethernet processor or comms card, since the new MAC address will not be recognised by the BOOTP relation list.

Click to expand...

This is the beauty of marcowy's system. The device's IP address is based on it's location. So if a device fails he just has to plug it into the line that the old device came from and the correct address is assigned. No configuration needs to be done to the device assuming it comes out of the box with DHCP or BOOTP enabled. The only real downfall is if someone gets happy fingers with the cables plugged into the switch the addresses get assigned wrong. But that is true of ANY conductor in a control cabinet.

Keith

kamenges said:

But that is true of ANY conductor in a control cabinet.

Keith

Click to expand...

May be true for any conductor, but Ethernet cables are something laymen are familiar with enough to the point that they may feel more comfortable trying to plug something in themselves. Similar to a standard 120V receptacle.

A maintenance employee is more likely to switch an Ethernet cable than they would be opening up a cabinet and moving wires around on terminal screws.

I've only met a couple of maintenance people that touched terminal wires in a cabinet. But I've met more than a handful that don't have any issues when it comes to plugs and receptacles. Including ones that have opened cabinets and disconnected encoder cable plugs from drives, then wonder why they lost position on the machine...

Originally posted by Tharon:

May be true for any conductor, but Ethernet cables are something laymen are familiar with enough to the point that they may feel more comfortable trying to plug something in themselves.
...
Including ones that have opened cabinets and disconnected encoder cable plugs from drives, then wonder why they lost position on the machine...

Click to expand...

You are correct. But in that environment you are effectively defeated anyway. At that point you can't use a standard Ethernet switch since the cables might get unplugged. That breaks you just as bad as plugging one into the wrong spot. As you said, you can't stop them from unplugging stuff anyway.

Keith

5 stars for this dicussion. Very educational. Thanks.

5 stars for this dicussion. Very educational. Thanks.

Click to expand...

I agree, but do have a question. Are there a lot of installations that follow this methodology?

lostcontrol said:

I agree, but do have a question. Are there a lot of installations that follow this methodology?

Click to expand...

The few systems I have that use Ethernet have setup IPs at the devices. It doesn't matter how or where they are plugged into the router/switch, as long as they are all on the same network.

Tharon said:

The few systems I have that use Ethernet have setup IPs at the devices. It doesn't matter how or where they are plugged into the router/switch, as long as they are all on the same network.

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THis is the most common way I have seen/setup PLC networks. With most devices you can save a copy of the program with the correct Ethernet Address. This way when you replace the device you simple reload the program and your ready to go.

Originally posted by Clay B.:

With most devices you can save a copy of the program with the correct Ethernet Address.

Click to expand...

I am guessing that most of the work you do is with vendors other than Rockwell. None of the adapters that I know of (1794-AENT, 1756-ENBT, etc) have a program per se. The addresses have to be set explicitly or service by a BOOTP or DHCP server. You at least have a shot with the drives if either the comma addapter survivied and you swap it into the new drive or if the HIM survived and you saved the paramters onto the HIM for both the drive and the Ethernet adapter (that second one gets forgotton quite regularly). If neither of these is the case and you saved the program via Ethernet you still need the Ethernet link correctly set before you can download the parameter set, which presumably contains the required IP address.

To be fair we set our IP addresses explicitly also. However, this has more to do with the switches we use than it does with concept. I like the concept of port specific IP address assignment in the types of systems I work on. I think it would ultimately save more time in component replacement than it would cost in cable location errors. It is as close to plug and play as you can get in many of these systems.

Keith

kamenges said:

I am guessing that most of the work you do is with vendors other than Rockwell. None of the adapters that I know of (1794-AENT, 1756-ENBT, etc) have a program per se. The addresses have to be set explicitly or service by a BOOTP or DHCP server. You at least have a shot with the drives if either the comma addapter survivied and you swap it into the new drive or if the HIM survived and you saved the paramters onto the HIM for both the drive and the Ethernet adapter (that second one gets forgotton quite regularly). If neither of these is the case and you saved the program via Ethernet you still need the Ethernet link correctly set before you can download the parameter set, which presumably contains the required IP address.

To be fair we set our IP addresses explicitly also. However, this has more to do with the switches we use than it does with concept. I like the concept of port specific IP address assignment in the types of systems I work on. I think it would ultimately save more time in component replacement than it would cost in cable location errors. It is as close to plug and play as you can get in many of these systems.

Keith

Click to expand...

Actually I work with AB some also... I guess I should be more specific...You have to get the program into the device with the correct IP adress...yes this is done with anything but Ethernet...because up to that point you have no address...

Example: Micrologix CPU dies... YOu take your program and load it via the serial port and if you saved it with the correct comm settings you are right back in buiness... You can do the same with drives if you have Drive explorer from AB...

I do see your point and it is something to look at

I just completed my first system using this method. 1 Stratix 6000 managed switch, 1 CompactLogix L35E Processor, 1 Panelview Plus, and 2 Powerflex 70 drives with ethernet comm cards. The first thing I did when we powered up the system was go online with the switch, and assign all of the ports their specific IP address.

After cycling power, all of my device IP's were set, and all I had to do was download my programs. I didn't have to touch a single serial cable, or mess with the panelview config screen.

It was very simple to setup. I did, however, clearly label each ethernet cable with which port it should be plugged into. I also made notes in the print that each cable went to a specific port. Hopefully that will prevent any 3am phone calls.

And what if the switch goes down and has to be replaced .......

Granted. You do need to program the switch to perform this function. And that may be just as difficult as setting the IP address on any given device.

So at this point, all other things being equal, we are talking about cummulative MTBF. Is it more likely that the switch will fail or that one of the eight devices connected to the switch will fail?

If you haven't noticed yet, I didn't say I'm going to jump out and convert all our system to this methodology. I'm just saying it is a perfectly valid method with alot of things going for it. To dismiss it as "asking for trouble" without a compelling reason sounds to me like "it's a bad idea because we do it another way and have never done it this way".

Keith