second instance using non-default broadcast port for who_is

[jerrys987]

Hi,
I have my application happily grinding away and keeping our house warm/cold nicely.
I am trying to run a test version in parallel to test new code before deploying it to the house. I have a while loop that starts at 47808 and finds the first unused port to set up the test version of the app in a separate running of the program. The problem is that the who_is broadcast is sent to the subnet broadcast (ipv4) with the alternate port, so none of my devices respond.
[tcpdump output]
23:08:50.191086 IP kea.47809 > 172.18.1.255.47809: UDP, length 18
I need the destination port to be 47808 for things to work.
It doesn't look like there is a command line arg to set this and it didn't look like the LocalBroadcast has a port attached. (I didn't fully understand the code, so this could be wrong.)

Did I miss something? How can I force the broadcast destination port to the default?
thanks,
jerry

[bbartling]

What you are looking for it how to route on different port numbers, right? One application that can communicate to devices on 47808 and 47809?

I think you can do that with a BBMD but I have never used those before. All my BACnet experiences even very large networks commercial building applications has all been on the same subnet and network port number thankfully :-)

[bbartling]

I am not familiar with how to use BBMD. Sorry you maybe able to surf some git issues. I have never had the use case to run multiple BACnet applications on a single device/OS.

[jscott3201]

I saw this pop up. One thing you can do on a Linux machine is to set up two IP addresses on the same interface. Eth0 might be your main one. You can create two IPs like 192.168.1.100 and 192.168.1.101 and use the same 47808 port. Bacnet in essence is binding to that port at that IP. This can be done in your local machine or setup in docker with compose and specifying service names.

ip or ifconfig are the usual options.

[jerrys987]

Justin,
thanks, I will have to try and see if it works.
netstat on my machine with just the main app running puts out:
netstat -an | grep 4780
udp 0 0 172.18.1.255:47808 0.0.0.0:*
udp 0 0 172.18.1.29:47808 0.0.0.0:*
You can see it binds the broadcast address as well as the local ip, which makes me concerned. I really don't care whether the second app can listen to broadcasts so it might be OK.

[jerrys987]

no joy. I started the second app with address 172.18.1.250/24:47808 and a unique bacnet address. the instantiation succeeds, but when I do a netstat I don't see the udp listener on the second address. I tested from another computer and the 250 address responds to ping. I guess it's back to figuring out the broadcast manager.

[jerrys987]

It doesn't work, but not in the way I said. The bind id deferred and does happen, but I never see the who_is packet when running tcpdump on the interface.

[bbartling]

bacpypes3 has support for BBMD

[jerrys987]

Thinking about it, if I could enable and disable BBMD dynamically, it could work fine.