Address and route BACnet requests across multiple networks using DNET/DADR notation and Who-Is-Router-To-Network discovery

Documented steps

1. Learn the Address syntax. Local station addresses carry no network prefix ('192.168.0.10', '12', '[fe80::9873:c319]'). Remote-station addresses are NETWORK:ADDRESS ('100:192.168.0.16', '100:12'). Route-aware addresses append @ROUTER ('200:192.168.0.19@192.168.0.20'). Broadcasts use '*' local, '100:*' remote network, '*:*' global.
2. Discover which router serves which network with the console command 'wirtn [address [network]]', or programmatically await app.nse.who_is_router_to_network(destination=address, network=network). It returns (NetworkAdapter, IAmRouterToNetwork) tuples whose iartnNetworkList names the reachable networks.
3. A router announces itself with I-Am-Router-To-Network, either unsolicited or in response. The console command is 'iartn [address [network]]' and the API is await app.nse.i_am_router_to_network(destination=address, network=network).
4. Inspect the local node's cached routing knowledge via app.nsap.router_info_cache.routers, which the 'nsap' console command dumps, and refresh a stale table with 'irt [address]' (Initialize-Routing-Table).
5. To run bacpypes3 itself as a router bridging two IPv4 networks, give each side's NetworkPortObject a distinct BACnet network number (for example 192.168.3.0/24 as network 100 and 192.168.7.0/24 as network 200) in a JSON app config, and run the router-json.py sample.
6. Address a remote device directly by DNET:DADR, e.g. 'read 200:192.168.7.2 analog-input,1 present-value'. The NPDU layer inserts DNET, DLEN and DADR and the local router forwards it.
7. If the destination network is not yet cached, the stack issues Who-Is-Router-To-Network on your behalf first. If that fails the request fails outright rather than degrading into a wider broadcast.
8. Access requirement: none cryptographic. Router configuration and network-number assignment are the practical control over what is reachable from where.
9. Official documentation verified 2026-07-30: https://bacpypes3.readthedocs.io/en/latest/gettingstarted/addresses.html | https://bacpypes3.readthedocs.io/en/latest/gettingstarted/running.html | https://raw.githubusercontent.com/JoelBender/BACpypes3/main/samples/router-json.py