Problem receiving UDP broadcast packets.

Grant Edwards invalid at invalid.invalid
Wed Apr 20 16:31:41 CEST 2011


On 2011-04-20, Dan Stromberg <drsalists at gmail.com> wrote:
> On Tue, Apr 19, 2011 at 6:15 PM, Grant Edwards <invalid at invalid.invalid> wrote:
>
>>> Or can you simply use a stupid netmask like /1 that picks up all the
>>> IP ranges? That way, the source-IP check wouldn't fail.
>>
>> That would require that the device somehow knows that it's not
>> configured correctly and should change the netmask to /1. ?The device
>> doesn't have any way to know that, and it must respond to the
>> discovery commands both before and after it's properly configured.
>
> - Actually, you Might be able to configure your device to have a
> netmask of 0.0.0.0, IP address of 255.255.255.255 and broadcast of
> 255.255.255.255.
> - I've seen something a bit similar used for detecting IP address
> conflicts automatically.
> - A network guru I used to work with told me that you could configure
> a machine with a broadcast of 255.255.255.255 more simply than messing
> around with the netmask, while still achieving the same result for
> general purpose networking.

I'll look into that.

>> I've reread the protocol documentation and noticed that the device has
>> to respond not only to broadcasts to 255.255.255.255 but also to
>> subnet broadcasts send to subnets it's not on. ?That pretty much
>> clinches the requirement to use a raw socket. :/
>
> With a netmask of 0.0.0.0, I suspect you will receive all broadcasts
> on the wire, given appropriate listening code.

That might be an option as well, as long as it doesn't disrupt normal
operation of the interface.

-- 
Grant Edwards               grant.b.edwards        Yow! Remember, in 2039,
                                  at               MOUSSE & PASTA will
                              gmail.com            be available ONLY by
                                                   prescription!!



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