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I have a Ubiquiti ES-16-150W and I must somehow route incoming UDP Unicast traffic to multiple computers. Ideally I would change the Unicast to Multicast but unfortunately the device which is sending the data is unable to send multicast traffic.

I know that it is possible to add another computer to the network and point the unicast traffic to it, and have it resend out as multicast, but there will be a great amount of churn with respect to the project requirements, documentation, diagrams, deliverables... the list goes on...

I have researched in many articles but due to my unfamiliarity with switch configurations and networking in general, I'm not sure this is possible by only changing the configuration in the switch.

Can someone please recommend to me a way that this can be done? Could I use NAT and route the UDP Unicast stream to a multicast address? It looks like this is not possible based on my research.

It looks like the many-to-one is common, but is there an opposite?

If Multicast NAT cannot be done, is it possible to somehow send incoming unicast traffic to two different addresses using some standard practice I am not aware of?

The receiver applications on the receiving computers are configurable to listen on multicast or unicast.

Any advice you can give would be much appreciated.

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  • You may be asking about an X-Y problem. Please edit the question to include the actual problem for which you are proposing this solution. Be sure to include a good network description or diagram.
    – Ron Maupin ♦
    Nov 25, 2020 at 17:15
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    cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_serv/… "Multicast Service Reflection"
    – Ricky
    Nov 25, 2020 at 17:22
  • @RonMaupin I do not think I am asking an X-Y problem. I have a device which is configurable to send Unicast UDP traffic to a specific IP and Port. I need this received at two devices simultaneously. The two devices are independent and may or may not be powered on (and therefore one cannot receive and also pass to the other). Any switch level configuration solution to this would be desirable.
    – NotJo
    Nov 25, 2020 at 17:38
  • This is not a switch-level configuration because IP is at layer-3, while switches are transparent layer-2 devices.. Why I am suggesting it may be an X-Y problem is that I wonder why you do not simply send multicast traffic in the first place. If you focus on the solution (convert unicast to multicast), rather than the real problem (the need to send the same packets to multiple devices), that is an X-Y problem because there may be more viable solution than the one on which you are focusing.
    – Ron Maupin ♦
    Nov 25, 2020 at 17:43
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    "it appears that multicast reflection relies on the incoming data already being multicast..." No, I think you missed this part: "or unicast destination addresses to multicast" Of course, this is for a Cisco router.
    – Ron Maupin ♦
    Nov 25, 2020 at 18:03

1 Answer 1

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It is possible to get a multicast-like effect by directing UDP traffic to an Ethernet Unknown Unicast Address. Configure a static ARP entry for the layer-3 address, e.g. 192.0.2.10 -> 42:00:00:00:2:10, and never originate any traffic from that MAC address. Traffic bound for 192.0.2.10 will then be flooded to all ports on the VLAN. Some switches work fine with this load, but some don't.

Your NICs would then need to be configured to receive traffic for that MAC address, either by adding it to their MAC filter, or configuring promiscuous mode. Similarly, your OS may need configuration to direct the UDP traffic to an application

You have to take care not to accidentally send any traffic from the related MAC address, or traffic will go onto to the port which sent it, not all ports. Therefore, this configuration is somewhat fragile.

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    I wonder if a NAT to the Limited Broadcast address would actually work better. The OP, in the comments, basically has control over the receiving application, so it could listen for the broadcasts, bypassing the IP address checking.
    – Ron Maupin ♦
    Nov 25, 2020 at 18:01
  • @Ron I think that's an idea worth exploring; I'm curious if his Ubiquity supports that configuration. Ricky's pointer to Cisco's unicast-to-multicast translation feature is probably the best idea if the OP had a Cisco router available on his network. Mainly, I posted the unknown-unicast answer to provide an alternative to the other solutions; unknown-unicast definitely isn't the best idea but could possibly work if others are unsupported by the available equipment.
    – Jeff Wheeler
    Nov 27, 2020 at 12:30

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