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I'm very inexperienced in networking, so please pardon any idiocy. We are mechanical engineers trying to connect weird hardware that talks on Ethernet.

We have a device A that can only send UDP broadcast packets. We have a device B that cannot read UDP broadcast packets. (Due to a silly firmware limitation...)

Our current workaround is to have device B set its IP address to 255.255.255.255, so it will read UDP broadcast packets as it thinks it is unicast to itself. We are in the process of adding new devices to the network, and would like to not have this hack, as we are afraid it will cause problems down the line.

So: Is there a way to copy a UDP broadcast packet to a UDP unicast packet to a selected IP address? We still want to be able to read the broadcast from other devices on the network. What kind of latency could we expect from something like this? We would be worried about anything greater than 1ms.

Any other ideas/suggestions/thoughts would be greatly appreciated.

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  • So, is it true that either Device A cannot send multicast, or Device B cannot receive multicast?
    – Mike Pennington
    Jun 13, 2015 at 9:17
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin ♦
    Aug 11, 2017 at 17:32

2 Answers 2

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There are many switches / routers that have a "helper" feature that will forward UDP packets. On Juniper EX switches for example you have forwarding-options helpers statement which is able to forward broadcast packets to other addresses. Still, you have only one address to forward when not doing bootp/dhcp.

Cisco has something like this with the ip helper feature but the last time I saw that it was limited to bootp/dhcp.

There are probably other Vendors which have gear that has similar features.

If you find a good reseller/partner they might let you try it out before buying.

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(If it lets you set the address to "all-ones", it is, indeed, broken.)

What you need is an application taking the broadcast frames and forwarding them as unicast to whatever needs it. No router or switch will do this in the manner you need. (Cisco's "helper address" might work for one device, but not for 2+)

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  • Why would "helper address" only work for one device?
    – Sebastian Wiesinger
    Jun 13, 2015 at 6:52
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    because you can only specify ONE helper address.
    – Ricky
    Jun 13, 2015 at 7:35
  • Thanks for clearing it up. I remembered incorrectly. On Juniper you can have multiple servers but only for bootp/dhcp.
    – Sebastian Wiesinger
    Jun 13, 2015 at 8:05

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