Multicast Comunication

I have a project working with various SNAP-PAC-R1 for some time. For customer requirements need to send ethernet frames to Multicast addresses (

In that project I’m using UDP frames sent to IPs within the range of SNAP without any problem.

In making the changes necessary to send the frame to a multicast IP, I found that the SNAP is able to send the frame (Whireshark), but the remote computers are not properly.

I think the problem is in the parameter of the frame TimeToLive UDP, which is 1, which does not allow more than one cross swicth / router. TimeToLive Parameter can be modified by any command TimeToLive as SendCommunicationHandle? would be possible to obtain all possible commands that allows this command?

The OptoScript example code:


Status_OpenCom = OpenOutgoingCommunication(SendMulticast);


Status_SendString = TransmitString(“MENSAJE DE PRUEBAS”,SendMulticast);

Sorry for my English

Hello mterron,

Welcome to the forums! Unfortunately, that default TimeToLive = 1 is NOT something which can be changed. I have submitted a customer request to Engineering to add a parameter to allow changing that TimeToLive parameter. However, that does not mean it can/will be added to the product.

Can you tell us more about the overall problem you are trying to solve? If you can give us the “big picture” it’s possible there may be another way to build a solution that could work for this situation.


Thanks for your answer.

I’ve been researching other options and may Protocol Ethernet/IP is the right choice for what I need to do.

In the documentation I have only seen Opto22 its configuration with Allen-Bradley PLCs PLCs, communication is possible with Omron PLCs?


Hi mterron,

I’m not familiar with Omron PLCs in particular, but I’m finding a lot of references on the web showing how to use what looks like a pretty simple serial protocol. Here’s one example:

You could implement the parts of that protocol you need in a chart or subroutine. Something like I did in this serial Optomux example chart.

FYI, also found this post which mentions a UDP option (vs. serial) for connecting to Omron you might want to consider. Here’s a post about [URL=“”]connecting via UDP that might be helpful too.


The use of the UDP protocol to communicate with Omron PLCs via FINS protocol, I’m currently using.
Currently send frames BroadCast for about 40 PLCs, as all must perform the same action simultaneously.

For installation requirements Broadcast use is prohibited, so if you do not want to send the messages one by one against the 40 PLCs, the client has asked me to use Multicast frames to reduce network traffic.

So wondering about using the Ethernet/IP protocol to write the order directly in the memory of the 40 PLCs.


Our Ethernet/IP implementation will not help you here, it’s designed to allow the SNAP PAC brains/controllers to receive or act as an “adapter.” So the PACs don’t initiate the communication like I believe you need to do here.

I’m wondering about your need to “reduce network traffic” – is this a wireless network? Also, to “perform the same action simultaneously” could be tricky even if multicast was an option, depending on the network and what exactly “simultaneously” means.

Perhaps the serial option might be worth considering? Looks like there might be a broadcast option there.