Re: [Bacnet-developers] DNET and gateway

[Derek N. <de...@pu...>]

I am still trying to solve this issue.

I have installed tshark on my linux device so at least I can see the bacnet
traffic.

 

The setup is as follows:

PC with BACnet client software at IP 155.247.120.90

PC is registered as a foreign device on BBMD at IP 10.124.44.63

My device 2700000 is at IP 10.124.44.94

Just to make things a little more difficult the subnet mask is 22 bits  L

 


	
	3352 2021-05-19 12:10:51,278265 10.124.44.63 10.124.47.255
BACnet-APDU 60 47814 Unconfirmed-REQ who-Is 3353 2021-05-19 12:10:51,278544
10.124.44.57 10.124.47.255 BACnet-APDU 68 47814 Unconfirmed-REQ i-Am
device,1045010 3354 2021-05-19 12:10:51,278605 10.124.44.94 155.247.120.90
BACnet-APDU 63 51948 Unconfirmed-REQ i-Am device,2700000
	
 

 

 

 

 

 


So the PC sends a broadcast who-is to the BBMD on port 51948

The BBMD resends the who-is shown on line 3352 on port 47814

Some other bacnet device responds with a broadcast i-am on line 3353 on port
47814

My device sends a unicast i-am direct back to the PC on port 51948

 

Given that the PC only sees the "other" device I assume the unicast message
is blocked.

 

Any help please.

 

 

Regards,

 

Derek Noffke

PurpleSwift

Cell: 082 780 4680

Tel: 021 761 8264

 

 

 

From: Dave Lindauer via BACnet-developers
[mailto:bac...@li...] 
Sent: Thursday, 13 May 2021 18:49
To: Derek Noffke; 'Discussion for developers of the BACnet stack'
Cc: Dave Lindauer
Subject: Re: [Bacnet-developers] DNET and gateway

 

Hi Derek,

 

Take me with a grain of salt.   I know quite a bit about bacnet over IP but
haven't spent extensive time setting up systems.

 

I suppose you set it up that way presuming the BBMD is on your current
subnet.   Then you wouldn't need to explicitly handle BBMDs I suppose.

 

But you are using multiple device objects routed at the same IP?   With the
root device being DNET 0 and the rest of them being DNET 2809?   I don't
think you should program the DNET of 2809 into the BBMD.   I think what
should be happening is you get the WHOIS broadcasts at the default DNET (0)
and the bacnet stack does some work to make sure all the device objects  get
it, since it is broadcast it can do that lol.    But the broadcasts will
come in PTP as forwarded broadcast messages.

 

And of course responses should have the appropriate SNET set.

 

Not sure at this point if we had to make a modification to make it do either
of those things though.   I know I modified that code, just cannot remember
why.

 

From: Derek Noffke <de...@pu...> 
Sent: Thursday, May 13, 2021 10:40 AM
To: 'Discussion for developers of the BACnet stack'
<bac...@li...>
Cc: Dave Lindauer <da...@po...>
Subject: RE: [Bacnet-developers] DNET and gateway

 

Thanks Dave,

 

I know very little about BBMD workings so any info is most welcome.  J

 

Client on site manually adds my root device 2700000 to his BBMD.

Discover works 20% of the time.

Client says problem is 2700000 is on DNET 0 while all other are on DNET 2809

 

Regards,

 

Derek Noffke

PurpleSwift

Cell: 082 780 4680

Tel: 021 761 8264

 

 

 

From: Dave Lindauer via BACnet-developers
[mailto:bac...@li...] 
Sent: Thursday, 13 May 2021 16:15
To: Discussion for developers of the BACnet stack
Cc: Dave Lindauer
Subject: Re: [Bacnet-developers] DNET and gateway

 

Generally the BBMD you want to talk to is on some other subnet.   To be
compatible with a BBMD you have to register with it at intervals (the
registration expires) so that you can get broadcasts from the other subnet.
Also in addition to broadcasting on your own network, you have to send your
broadcasts directly to the BBMD in point to point fashion so that they can
be received on the other network.   For example the IAM messages.

 

There is specific protocol related to this, but the bacnet stack has helpers
and so forth.    There might be an example as well.    I found it pretty
easy not only to interact with BBMDs but to create one for testing!

 

David

From: Derek Noffke <de...@pu...> 
Sent: Thursday, May 13, 2021 8:59 AM
To: bac...@li...
Subject: [Bacnet-developers] DNET and gateway

 

Greetings,

 

I have an app based on the gateway demo code.  BACnet Stack Version 0.8.4

I have been informed that my gateway is not compatible with a BBMD.

 

The startup I-AM sequence is attached.

I see that the I-AM for my "root" device 2700000 does NOT contain the DNET.

Is this possibly the problem?

 

Regards,

 

Derek Noffke

PurpleSwift

Cell: 082 780 4680

Tel: 021 761 8264