RsLogix Multicast IGMP Question

[bulletin blues]

Hello.

I have a question about multicast packets over produced tags.

I've got a home lab setup, and I'm trying to get a better understanding of my cisco switches.

I have a controllogix rev 19, 4 slot chassis. I have a processor in slot 0, and 1756 enbt in slot 1. I have another processor in slot 2, with a second 1756 enbt in slot 3.

Both of the ENBT's get tied to some various other cisco switches, which get trunked back to a 3550.

I have a produced tag from the processor in slot 0, sent out the enbt in slot 1 to a switch. It is being consumed by the processor in slot 2, via the some cisco switches back into the enbt in slot 3. This is working properly, as when I modify the produced tag values in the first processor, it gets updated in the consumed tag processor.

I DO NOT have the use UNICAST selected in the produced tag configuration. This should be multicasting, and I would think that I would see some multicast memberships in the IGMP stats in each of the processor web pages. But I don't.

I also don't see any multicast info in my cisco switches.

I'm running wireshark to see what I can see, but I'm just seeing direct source to destination addresses between the processors, not the default multicast (239.x.x.x, etc) addresses between processors. I'm also doing some routing, which may also be complicating the issue. It may be worth it to unplug everything and just set them all to the same subnet and plug into one switch, but everything else seems to be working.

Also, I've got a myriad of USB network adaptors, connected to usb hubs, running through vm's that may be complicating the issue.

Is it possible that Logix is sending the tags through the backplane?

Any insight is appreciated.


Thanks.

 

[AustralIan]

My understanding is igmp multicast is only for a local subnet.
Maybe it knows it can only use unicast over a different subnet.

To answer your only question: No.

 

[bulletin blues]

I put both enbt's on the same subnet. Still no multicast between produced/consumed tags.

I added a point IO module, and that is showing a multicast address in the processor web page.

I just figured produced and consumed tags were multicast if "use unicast" was not selected. Maybe not between processors though?

This is just a test bench to break stuff on, which I'm succeeding. I'd rather figure it out here than in the field.

Also, I forgot to set up port mirroring/span on the switches to see whats going on per port. I will look at that next.

 

[drforsythe]

I thought that when you set up produced / consumed tags, you are automatically creating unicast messages, because you have specific IP addresses defined. Am I wrong? If so, please clarify for me. I am not an expert on this subject and trying to learn more.

 

[Contr_Conn]

In recent versions, when you create Consumed tag for a Producer on Ethernet, unicast box is checked by default. You can uncheck it to get multicast.

Same on Producer side - "Allow Unicast" is checked by default.

 

[dmargineau]

How many 'Consumers' were defined when the 'Produced' tag was created?

Your at-hand topology implies that there is only one hence the apparently 'Unicast' communication implementation.

Try adding another 'Consumer' CPU 'consuming' the same Non-Unicast 'Produced' tag. With two active 'Consumers' you will probably detect the sought Multicast traffic.

 

[scott.maddox]

Once you get it multicasting in order to get it working across different subnets you will need to enable a multicast routing protocol such as PIM or OSPF. If you have Cisco switch you will need the correct licensing to do those types of functions.

 

[Contr_Conn]

I am not sure if it can be routed because TTL=1 for all class 1 multicast packets.