BBMD / NAT
BBMD connects BACnet IP networks that are not on the same local network (see
BACnet IP
BACnet/IP uses the User
Datagram Protocol (UDP) to send data packets. ASHRAE adopted BACnet/IP
in annex j of the 135- 1995 standard.
BACnet/IP communicates using four methods.
• BACnet/IP to BACnet/IP (same subnet): Assuming that two devices know each other's IP addresses
and the UDP ports they are using, i.e., their respective B/IP addresses, there is nothing that restricts
them from communicating directly.
• BACnet/IP to BACnet/IP (different subnet): The location of the two devices is already known by the
host and the message is routed to the device using switches and routers.
• Broadcast (same subnet): This is a standard Who is/ I am message sent across a local subnet for the
BBMD to discover what the address are for the BACnet devices on the subnet.
• Broadcast (different subnet): This is a standard Who is/ I am message sent across a local subnet for
the BBMD to discover what the address are for the BACnet devices on other subnets.
BACnet IP Broadcast Management Device (BBMD) on page 17 for details).
NAT connects sites where there is a NAT gateway between them.
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