Planning your network - Metasys - LIT-12012458 - Field Device - 13.0

Metasys IP Networks for BACnet/IP Controllers Technical Bulletin

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The maximum number of Metasys devices that can be supervised by a network engine is independent of the transport used to connect the Metasys devices to the network engine (MS/TP vs IP). The maximum number of devices which can be supervised by a network engine depends on multiple factors such as the number of objects supported by the network engine and the quantity and rate at which the devices send Change Of Value (COV) messages to the network engine . In this section, all examples are based on network engine s that support 200 BACnet/IP Metasys devices.

Note: For information on limits and further information about network engines , refer to the NAE85/SNE/SNC Product Bulletin (LIT-12013296) .

With MS/TP, the scope of the Metasys devices that a network engine could supervise was limited to the following:

  • The devices physically connected to an MS/TP bus that was physically connected to the network engine .
  • The devices physically connected to a remote MS/TP bus that was logically connected to the network engine through an IP connection.

For the purpose of network planning, the containment scope of a network engine and the Metasys BACnet/IP devices that it supervises, is one VLAN and one IP subnetwork that are usually defined to overlay each other. However, a remotely located BACnet/IP controller in a different VLAN and subnetwork can be logically mapped to a network engine by deploying the remotely located device with a BBMD. For a network engine that supports 200 IP controllers, it is recommended that a Class C IP subnetwork, which supports up to 254 usable IP addresses, is allocated. A Class C network such as can either be represented by a subnet mask of or in the Classless Inter-Domain Routing (CIDR) format

Unless otherwise noted, it is assumed that the Metasys server is connected directly to the IT network; as such, its configuration is beyond the scope of this document. It is also assumed that the Metasys server has a well-known identifier, either a static IP address or a name (a name requires use of the IT department's Domain Name System (DNS) name server).

The following types of connections are used when configuring switch ports:
Access port
An access port carries traffic only for the VLAN assigned to the port.
Trunk port
A trunk port is by default a member of all the VLANs that exist on the switch and carries traffic for all those VLANs between the switches (OSI Layer 2). A trunk port can be configured to carry traffic from only a subset of the VLANs that exist on the switch. Trunking is a function that must be enabled on both ends of a link.
Routed port
A routed port is a physical port on a switch that acts like a port on a router (OSI Layer 3). It supports all routing protocols. It does not support VLAN sub-interfaces and is not associated with a single VLAN (OSI Layer 2). It is configured on a port connected to a router and is assigned an IP address.

The acronym SVI is used frequently in the text that follows. SVI stands for "switched virtual interface" (or in other texts, for "switch virtual interface"). The physical interfaces of a switch are where cables are connected. In the following architectures, a single cable may carry data for several VLANs. It is useful to create virtual interfaces so that the data on each VLAN can sent somewhere for forwarding, similar to a gateway. An SVI gives the switch some routing capability.