tight-wad ethernet question.

Is it OK to connect two different ethernet networks to the same switch?

Example:
Plant Network computer 10.11.201.[DHCP] + ControlLogix ENBT card in slot 1, 10.11.201.55 + ControlLogix ENBT card in slot 2, 192. 168.0.1 + panelview 192.168.0.1 + drive 192.168.0.3 + drive 192.168.0.4 + remote IO 192.168.0.5

I don't think that would work, but you could put another ENBT in either of the ControlLogix chassis to bridge to the "other" network.

Alaric said:

Is it OK to connect two different ethernet networks to the same switch?

Example:
Plant Network computer 10.11.201.[DHCP] + ControlLogix ENBT card in slot 1, 10.11.201.55 + ControlLogix ENBT card in slot 2, 192. 168.0.1 + panelview 192.168.0.1 + drive 192.168.0.3 + drive 192.168.0.4 + remote IO 192.168.0.5

Click to expand...

I would put a second network card in the computer, go static, & bridge through it.

Just try it.

I think it will work. After all the switch doesn't know anything about IP masks.

http://www.ab.com/networks/site-index.html

is a page on ab.com one of the powerpoint slides goes over putting a switch between plant computers and plant devices(drives etc.) and compares this withe two enbt cards on a clx rack.

cheers

myles

I'm with Peter. I THINK it will work. The switch will pass data between any two ports on a common subnet. The fact that you are dealing with two subnets in a single device shouldn't change that. But I don't have enough toys just laying around here to try it.

I suspect Nathan or Archie will have something to say about this.

Keith

Yes, definitely, you can connect all those devices to a single Ethernet switch and successfully communicate among the separate network subnet devices.

Your concern should be with the effect that the UDP Multicast traffic from the drives and remote I/O adapter will have on the office network to which this switch is connected. If this switch lacks an IGMP Query/Snooping feature and the upstream switches also lack IGMP Query/Snooping features, then you may become unpopular, and possibly notorious, among your colleagues in short order.

Any managed Ethernet switch will have this capability. I prefer the rugged Hirschmann RS20 or NTron 508-A or 7014TX, but have certainly used more office-grade switches like a Cisco 2950 or HP Procurve 2500 series. These may not be in line with your highly-compressed wadding ethos, but do save you remarkable amounts of confusion, effort, and recrimination.

I'm making a (probably bad) assumption here. But I'm guessing that Alaric's configuration has the macine stuff on one subnet and the 'office' stuff on another.

I'm certainly no expert with this so this may not be right. But I didn't think a switch would pass a multicast message to something on a different subnet from the source?

Keith

It depends on the switch. Most common switches allow multicast traffic.

Basically, your performance will suffer from doing this. Even though switches route traffic efficiently, there is a lot of underlying broadcast traffic that industrial ethernet devices create that will be multicast. This will splatter across both networks and your nice fast network will no longer be as fast or robust as it was before.

Either put in a managed switch, use a computer with two NICs to bridge, or add a second ENBT to the PLC.

It sound like "tight-wad" Alric would rather spend the money for two regular switches rather than one managed switch anyway.

The plant I used to work at did it with managed switches. The only thing I don't remember is if there was some fancy configuration trickery to get it to work. I suspect there wasn't anything fancy because the guy's that originally set it up weren't really that sharp.

The reason I ask the question is I want to put a programming port in enclosure door so that it is not necessary to open the door to plug into the switch (arc flash regs). I can put in two ports and label each one, or, if I route both networks through the same switch then I need only one port in the door.

dmroeder said:

It sound like "tight-wad" Alric would rather spend the money for two regular switches rather than one managed switch anyway.

Click to expand...

kamenges said:

I'm making a (probably bad) assumption here. But I'm guessing that Alaric's configuration has the macine stuff on one subnet and the 'office' stuff on another.

Click to expand...

Thats the problem with assumptions. Sometimes you're dead wrong. Sometimes you're right.

In this case dmroeder your assumption is dead wrong.

I always use managed switches for control networks. The question deals if whether a second switch is necessary or not.

Keith, your assumption is right on the money.

The CLX rack contains two ethernet cards, one of which connects to the office network and the other is control network. We connect all of our PLCs to the office network so that we can program/monitor the PLC and collect data from the engineering offices. We however do not mix IO networks with office networks - but by using ENBT cards we bridge between the networks to access a drive or panelview from the office.

If I carry my laptop to the plant floor to be in front of the panel, I also still want plant network access so I can access drawings, manuals, etc, and the laptop will be plugged into the switch - meaning that if I leave the etherent port configured for DHCP I will be accessing the PLC through slot 1 ENBT card and bridging to the etherent IO on the slot 2 ENBT, or I can set it static and connect through slot 2 ENBT - but in either case be plugged into the same port.


Thanks everyone for all your comments. I'll give it a try, if I run into problems then I can always plug in another switch.

Alaric said:

In this case dmroeder your assumption is dead wrong.

Click to expand...

Hopefully no hard feelings, that was just my attempt at humor.

AD doesn't even use IP!!!! It works

The switch doesn't care about IP packets, just MAC addresses. We have a AD 250 PLC with Ethernet that we use for testing. Orignally AD just send raw Ethernet packets back and forth. They went thought the switches without problems. These packets were not routable though.

Icky812 should be able to back this up. I thought he is a AD guru.

dmroeder said:

Hopefully no hard feelings, that was just my attempt at humor.

Click to expand...

None at all, hence the emoticon.

Assumptions come with pitfalls - I get into lots of trouble myself over them.

I appreciated your input on your experience about doing it at the plant where you used to work.

kamenges said:

I'm certainly no expert with this so this may not be right. But I didn't think a switch would pass a multicast message to something on a different subnet from the source?

Click to expand...

Broadcast traffic should be limited to the subnet (alternatively known as a broadcast domain).

http://en.wikipedia.org/wiki/Broadcasting_(computing)

Multicast is a bit of a different beast though and is intended to send the same data to multiple interested destination nodes on the local or wide area networks. IGMP is a multicast protocol for managing multicast traffic at the local network level.

http://ntrg.cs.tcd.ie/undergrad/4ba2/multicast/
http://en.wikipedia.org/wiki/Internet_Group_Management_Protocol