Planning a converged Metasys BACnet/IP network - Metasys - LIT-12012458 - Field Device - 13.0

Metasys IP Networks for BACnet/IP Controllers Technical Bulletin

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In the Converged Metasys BACnet/IP network architecture, all IP addresses are allocated from the IT network's address space, but the Metasys BACnet/IP devices are physically connected to switches which are dedicated to the BAS network.

Johnson Controls recommends that a VLAN and IP subnetwork be allocated for each network engine and the BACnet/IP controllers that it supervises. At minimum, the following static IP addresses are required to be reserved within each subnetwork:
  • A static IP address for the SVI for the VLAN. An SVI acts as the default gateway and is required for the network engine to communicate with the Metasys server and with other network engines in other VLANs. The host number of the SVI and the location of the SVI within the IT network is left to IT.
  • An IP address for the network engine . The IP address of the network engine is statically assigned at the network engine , although it could be dynamically assigned by the DHCP server using a static binding to the network engine 's MAC address, configured at the DHCP server.

In addition to the static IP addresses in the BAS VLAN listed in Table 1, if IT uses a dedicated switch management VLAN, then IT must configure an SVI for the management VLAN on the BAS switches for management purposes (for remote access to the switch to review and/or update the switch configuration, restart the switch, or other management purposes).

The IP addresses of the IP controllers must be dynamically assigned by way of DHCP. If the IP controllers are to be dynamically assigned, a small number of extra IP addresses (for example, 10) must be reserved in the DHCP scope so that they are available if a BACnet/IP Metasys device needs to be replaced. All IP addresses for the Metasys BACnet/IP devices must be allocated from a contiguous range within the middle of the subset. The IP addresses of the devices can be:
  • allocated by the IT DHCP server
  • allocated by a DHCP server on the Metasys BAS switch

The IP address can be dynamically assigned, or each Metasys device can be assigned to a specific IP address using a static binding to the MAC address of the device (requires additional configuration in the DHCP server). As an advantage of using a static binding to the MAC address of the device, you get static IP address assignment by using DHCP. That is, the DHCP server always assigns the configured IP address to the device. This allows the IP address mapping to be done in a central location (in the static binding table in the DHCP server) rather than requiring each controller to be individually configured with a static IP address. The drawback to using static binding is that the MAC address in static binding table in the DHCP server must be updated whenever an IP controller is replaced.

When possible, contiguous VLANs and IP subnetworks must be allocated for the VLANs and subnetworks that comprise the BAS network.