Using multiple IT VLANs - Metasys - LIT-12012458 - Field Device - 13.0

Metasys IP Networks for BACnet/IP Controllers Technical Bulletin

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The network engine s and BAS access switches can also be connected through multiple IT VLANs. This can occur if:
  • IT does not want to allocate a new VLAN for the BAS system and instead allocates a subset of addresses to the BAS system from multiple existing VLANs/subnets.
  • IT does not want to propagate a VLAN across all the IT switches to which the BAS access switches and network engine s would need to connect and instead allocates switch ports assigned to existing VLANs.

In this case, each BAS access switch is connected to an existing IT VLAN corresponding to where the BAS switch physically connects to the IT network. This approach is similar to connecting a remotely located Metasys device. This approach is IT-friendly in that it does not require IT to dedicate a VLAN or subnetwork to the BAS network, nor propagate an additional VLAN throughout the IT network. It does not, however, isolate the BAS traffic from the other devices residing within the existing IT VLAN(s). Also, the IP packets from the controllers in the BAS private address space cannot be routed by the IT network switches. Therefore the IP controllers connected to a BAS access switch in one IT VLAN cannot communicate with IP controllers connected to a BAS access switch in a different IT VLAN. This also means that peer-to-peer references cannot be established between IP controllers connected to BAS access switches in different IT VLANs.