[PD] Get IP from Pd + network broadcast

Christof Ressi info at christofressi.com
Fri Jan 22 23:14:19 CET 2021

> [netreceive] reports the source address for received data only
> for TCP connections, but not for UDP
[netreceive -u -f] works just fine for me on Pd 0.51 ;-)


On 22.01.2021 22:52, Roman Haefeli wrote:
> Hi João
> On Fri, 2021-01-22 at 19:41 +0100, João Pais wrote:
>> I wanted to check if there are any new methods to get one's own ip
>> from Pd - that is, so that a user doesn't go check the system
>> settings.
> I need that, too, and I can't wrap my head around figuring out how to
> do it. Using a [shell]-like solution would require different scripts
> for each platform. Also, "knowing" the IP address is not that trivial:
> A computer might have many physical network interfaces (ethernet and
> wlan) and a localhost interface and even has more when hosting virtual
> machines and VPN is configured, etc. I count 10 addresses on my laptop.
> So, which is the one you're interested in?
> Usually, it's the other party (that you're connecting to) that knows.
> For a specific connection, the other party knows the address that is
> interesting in the context of that particular connection. In Pd
> vanilla, [netreceive] reports the source address for received data only
> for TCP connections, but not for UDP. iemnet's [udpreceive] will tell
> you the sender, though.
> There is no deterministic way to define your own address. Depending on
> the destination, packets might be routed differently and thus the
> source address will be different. If you know the destination address,
> you could parse the routing table and deduce the (your) source address
> from it.
>> It would be necessary for all windows, macos and linux. Older
>> messages talk
>> about using [shell] in unix systems, and some hack with a batch file
>> in
>> windows. If this is still the current method, how would one activate
>> a
>> batch file in windows from inside pd?
>> As my knowledge of network isn't that good, just to check: to send a
>> broadcast message for all peers in the same network, is the correct
>> IP
>> e.g. xxx.xxx.xxx.255?
> Depends on the kind of subnet. If your netmask is, then
> yes. But networks can be of any size and depending on the size, the
> broadcast address of that network might be a different one. The IP-
> Address in a local network is divided in a network-prefix and host
> part. You see often addresses specified in CIDR notation, for example:
> The '24' means that the first 24 bits of the address
> are the network prefix, and the remaining 8 bits is the host part. For
> getting the broadcast address of a given subnet, you set all bits of
> the host part to 1, which results in x.x.x.255 for a /24 network.
>>   I read somewhere that was also for
>> broadcast, but since it's not working I imagine I read wrong.
> It's the broadcast address of the subnet, a.k.a the whole
> IPv4 internet. However, routers do not pass broadcast message from
> local network to the internet. But at my home, I can send messages to
> all my devices using this address.
> Note: it works only with shoot-and-forget protocols like UDP, but not
> with connection-aware protocols like TCP.
> Also, I'm not sure if all routers pass on such messages.
>> Resuming: to send a broadcast message in the network, it's necessary
>> to
>> know the first 3 parts of one's IP?
> In my experience not. Just use
> Roman
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