IPv4 Communication Fundamentals
20 ECLYPSE User Guide
Networking Basics
When manually configuring the TCP/IP interface on an ECLYPSE IP controller (the DHCP
option is not used), an IP address, subnetwork mask, and a default gateway are required in
the Network Settings.
IP Addressing
The most widely used internet addressing scheme is IPv4. It codes an IP address in 32 bits.
An IPv4 address is made up of two parts defined by a subnetwork mask; the network portion
(which identifies a specific network or subnetwork) and the host portion (which identifies a
specific device).
About the Subnetwork Mask
Devices on the same sub-network can address IP packets to each other directly without
routing. The range of IP addresses available in a sub-network is defined by the subnetwork
mask. This is also called the subnetwork mask’s ‘address space’. The subnetwork mask is
coded in 32 bits as follows.
An IP packet addressed to a device on another network portion will have to be routed
through the router’s WAN port as such an address is not local. BACnet/IP broadcast
discovery messages such as “Who-Is” do not pass through network routers that separate
subnetworks. This means that BACnet/IP controllers on different subnetworks will not
normally communicate with each other.
BBMD allows broadcast message to pass through a router: on each subnet, a single device
has BBMD enabled. Each BBMD device ensures BACnet/IP connectivity between subnets
by forwarding broadcast messages found on its subnetwork to each other, and then onto the
local subnetwork as a broadcast message. See BBMD Settings on page 80.
Number of Subnetworks
according to the Network Type
Number of Hosts according to
the Network Type
CIDR Addressing
Another way to express the subnetwork mask is through CIDR addressing (Classless Inter-
Domain Routing) which is written as a slash and a number which represents the number of
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