Ethernet IP Router

The Plc Kid

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Feb 2009
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I have a customer that wants to exchange about 12 words of data between 2 logix controllers that have managed switches but are on seperate networks that they want to keep seperate so they will need a router. They have a small budget so they want to use a cheap router in the middle (linksys) to route traffic between the 2 machines.

I assume a home use linksys router is unmanaged? I think they will have problems with this setup but given the small amout of data exchange they want me to try it. Opinions?
 
I believe that the last linksys router I bought (~$40-$50) was able to download a new firmware program, and be used as a managed switch to do just about anything you wanted. But I'm sure going that way while would be cheap on hardware, would not be so on your time.

-Brian
 
Does the router need the IGMP snooping features also since it is Ethernet IP?

?? :unsure:

Over my head... I just plug them in and they work :)

I have a 30day money back if you are not happy for any reason, I use them all the time with 1756-ENBT 's and 1769-L32/35's they work great

I do know they have a configuration web page but I have not had to get into them...
 
The simple answer is maybe

The Linksys BEFSR41 is a great little router for home use. For the very limited role and specific functions that it performs, it is reliable and cheap. I've certainly found them to be far more reliable than their fancier wireless counterparts, even with open-source project firmware loaded.

The problem with the function you need to perform is that the BEFSR41's main role is to be a Network Address Translation firewall. Everything on the LAN side runs privately, and it will forward connections that originate on the LAN side to the WAN side, but block every connection that originates on the WAN side.

Prior to v16 of RSLogix 5000, such a discussion would be a non-starter; the UDP Multicast traffic used by I/O connections and Produced/Consumed Tags won't cross any kind of router because the Time To Live (TTL) parameter is hard set =1, and every router decrements that by 1 when it passes a packet.

v16 of RSLogix 5000 allows an option to perform Produced/Consumed tags between just two devices (you cannot have multiple consumers) using a Unicast target address. I believe such a packet can cross a router.

v18 of RSLogix 5000 provides similar functionality for single-owner I/O connections.

The BEFSR41 might work with Unicast Produced/Consumed Messages if the Consumer is on the LAN side. The Consumer's requests will go through the router to the WAN side, and replies to those requests will come back. UDP Unicast packets produced by the Producer *should* also pass through the router.

The BEFSR41 also might work with Unicast Produced/Consumed Messages if the Consumer is on the WAN side and you configure the IP address of the controller on the LAN side to be in the "DMZ", or if you configure port forwarding to send Port 44818 only to the IP address of the controller on the LAN side.

That's two "mights" and a "should". Not something I'd strut confidently onto the factory floor with, but in my opinion it can't hurt to try, since the small budget is their idea.

My principal concern is not the DMZ or the Port Forwarding or the Multicast filtering, but rather any possibility that the router will attempt to perform some kind of inspection on the Produced/Consumed packets flowing from side to side of the network. If there is any kind of antivirus firewall or "stateful packet inspection" going on, the router will probably choke in a hurry on thousands of tiny packets a second. One of my colleagues broke a BEFSR41 irrevocably on a test bench when he turned off IGMP snooping and the router attempted to analyze a few thousand I/O packets per second. It wouldn't even hard-reset... he had to throw it out.
 

Like I said way over my head... I am not a network/IT guy



One of my colleagues broke a BEFSR41 irrevocably on a test bench when he turned off IGMP snooping and the router attempted to analyze a few thousand I/O packets per second. It wouldn't even hard-reset... he had to throw it out.

The 30 day money back does not apply if you do this :eek:
 
They have some stratix 8000 switches in their plant so i am trying to get them to just put a stratix 8300 that will route on one of the machine and be done with it because i know that works flawless.
 
How are you setting up the comms. Are you using a MSG block, or a produced/consumed tag? The message block should route no problem, but routing multicast messages will be problematic. If these switches are managed, they should have some routing capabilities. You only need IGMP if you are using multicast messages.
 
GF i have not went that far with it yet but most likely a message instruction because it will only use 1 connection where produce/ consume uses 1 connection per tag.

To the best of my knowledge all ethernet traffic on the logix system is multicast until v18 where unicast is an option. The stratix 8000 are managed with IGMP Snooping but are only layer 2 and will not route between subnets.

Ken from your reply just to cure my curiosity how was routing done prior to v16 with the TTL parameter problem? That is intresting because it is the first time i have known of that. I learn something new with ethernet on every post. Is the TTL parameter set higher that 1 in v16 and higher?
 
Doesnt sound like they need a router. You said they have managed switches in place. They should be able to setup a Virtual LAN (VLAN) between the two PLC's using the managed switches already in use. This will allow the two PLC's to talk but will not allow other devices on the switches to talk through the ports that are setup (if properly configured - of course). Talk to your IT guy about VLAN's
 
True we could make a vlan between the 2 switches but you have to get that data into the plc. Then you would need an additional enbt on each end to get the vlan traffic into the processor correct?

Machine 1 is 10.10.140.xxx and machine 2 is 10.1.50.xxx now we make a vlan between the 2 switches like 10.10.30.xxx and traffic will flow between those 2 ports but you have to get into the plc and the options are additional enbt on each ( Which these is no room for in the chasis on machine 2) or you are back into a routing situation the way i understand it.

Am i looking at this wrong?

What other method of getting the vlan traffic into the plc could be used other than additional enbt's? To the best of my knowledge a single enbt can only handle traffic from 1 network of which it's ip address is in the correct range?

BTW our IT guy is more or less useless he knows less than i do and is very lazy.
 
BTW our IT guy is more or less useless he knows less than i do and is very lazy.

Ha! I guess we can all assume that he doesnt visit this forum either...

I wasn't even thinking about the two systems being subnetted differently. You would really only need an additional ethernet card on one of the systems, but that seems cost prohibitive to me. I am not an IT guy nor do I play one on TV (old joke), however I think you can allow those two PLC's to talk if the subnet mask is set to allow it. I think a subnet of 255.255.65.0 would allow the two stations to talk. Now - I am not sure of the ramifications of opening up your masking like that. Maybe, just maybe, the IT guy can help with that? Maybe an IT forum?
 
Anyone know of a fairly inexpensive DIN rail mountable ethernet router? I don't know if a customer will want a Linksys BEFSR41 sitting in the bottom of a control panel. They usually insist on something a bit more 'industrial' looking...
 
I use/install Hirschmann, I have a bunch so I have not had to buy one in a long time... so not sure of the price
 

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