While ASHRAE and the building automation industry are just beginning to adopt the IPv6 addressing standard, it was defined more than 20 years ago in response to the limited address space of IPv4, which provides roughly 4 billion possible addresses—an amount that could not sustain the rapid growth of connected devices.
IPv6 solves this limitation by increasing the range of available addresses from 232 (32 bits) to 2128 (128 bits). To put that in perspective, IPv4 supports about 4 billion addresses, while IPv6 supports around 340 undecillion addresses—a 3 followed by 38 zeros!
Despite the introduction of IPv6 more than 2 decades ago, IPv4 remains widely used. Network Address Translation and Dynamic Domain Name System technologies have extended the usable life of IPv4 by allowing internet service providers to conserve address space. As a result, IPv4 network addressing is likely to be used for many years. At the same time, IPv6 adoption is already widespread in ways that aren’t always visible. Most smartphones rely on IPv6, and many internet service providers use it in their global networks.
Why IPv6 matters for building automation
The shift to IPv6 is being propelled by governments and large institutions. In addition to its expanded address space, IPv6 improves network performance and security.
The good news is that networks using IPv4 and IPv6 can operate together, allowing for a gradual transition as organizations build the expertise required to support IPv6.
IPv6 concepts you should know
The first concept to understand is IPv6 address structure. IPv4 addresses consist of four 8-bit numbers shown in decimal notation (0–255) separated by periods:
Bottom of range
0.0.0.0
Example address
92.168.1.100
Top of range
255.255.255.255
IPv6 addresses consist of eight 16–bit numbers shown in hexadecimal notation (0–ffff) separated by colons:
Bottom of range
0000:0000:0000:0000:0000:0000:0000:0000
Example address
2001:0db8:0f61:a1ff:0000:0000:0000:0080
Top of range
ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Each 16–bit hextet is called a chomp. IPv6 addresses are long and often contain repeated zeros, so standard abbreviation rules are used to shorten them.
- Leading zeros in each chomp are omitted: 0db8 becomes db8.
- A chomp of all zeros is abbreviated to a single zero: 0000 becomes 0.
- Consecutive chomps of zeros are replaced with a double colon: a1ff:0000:0000:0000:0080 becomes a1ff::80.
To avoid ambiguity, only one sequence of consecutive zeros can be replaced with a double colon, and it should not be used for a single chomp. The abbreviation rules are applied below:
- Example address: 2001:0db8:0f61:a1ff:0000:0000:0000:0080
- Abbreviated example address: 2001:db8:f61:a1ff::80
The eight chomps of an IPv6 address identify both the subnet that a device is connected to and the device’s interface ID. Most commonly, the first four chomps define the subnet prefix, and the last four define the interface ID.
In this example, 2001:0db8 is assigned to a specific internet service provider (ISP). The ISP then allocates 0f61 to a subscriber site for a large institution, and the institution defines a1ff as a local area network (LAN) segment in a building.
This structure allows for 18,446,744,073,551,616 unique IP addresses that can be routed in a single IPv6 LAN. It also enables end-to-end routing between devices across wide area networks (WANs) and over the internet.
Multicasting vs. broadcasting
A challenge in BACnet/IP systems is their reliance on broadcasting. BACnet automatic discovery, alarm notifications, and other services use broadcasts to send messages to all reachable devices on an IP network.
This approach puts a heavy burden on IT infrastructure and can lead to data storms that disrupt entire networks. This is because a single device can send messages to every device on a network segment.
To prevent broadcasts from propagating across the internet, IT routers block broadcasts from WANs and the internet. As a result, BACnet/IP systems require BACnet Broadcast Management Devices (BBMDs) to communicate across network boundaries.
IPv6 does not support broadcasts. Instead it uses multicasts, which allow one device to send messages to many devices.
To define which devices receive a multicast, special multicast addresses are used. Each device subscribes to a multicast scope and receives messages sent to that scope.
All multicast scope addresses begin with FF. BACnet defines six scope addresses, which all end in BAC0.
For example, FF02:0000:0000:0000:0000:0000:0000:BAC0 is abbreviated as FF02::BAC0.
The scope assigned to a network interface port defines where multicasts are delivered in the internetwork:
FF01::BAC0—Interface-local or node-local
This is the most restrictive scope, as multicasts remain local to the same device. This scope can be used for communication between RC-RemoteAccess and RC-WebView software from Reliable Controls running on the same server.
FF02::BAC0—Link-local
This scope is the closest equivalent to how BACnet/IP broadcasts work. Messages reach devices on the same LAN segment behind a single IT router or a single subnet.
FF04::BAC0—Admin-local
This is the first multicast group that requires IT configuration of the routers. This intermediate scope targets part of a site. For example, a tenant occupying three floors of a 10–floor building could be grouped using this scope.
FF05::BAC0—Site-local
This requires IT router configuration. It’s intended for a multicast scope at a single site like a building.
FF08::BAC0—Organization-local
This scope requires configuration across a private WAN and can be used for multicasts to span multiple buildings in the same organization.
FF0E::BAC0—Global
This scope requires extensive router configuration and is intended for routing over the public internet. Most ISPs block multicast traffic, making this scope unlikely to be used.
Usually only two multicast scopes are used: FF01::BAC0 for communication between software running on the same server and FF02::BAC0 for typical BACnet networks. Any other scopes in use are defined and managed by the IT team responsible for the network.
Although BACnet systems can be configured to allow multicast traffic to cross IT routers, multicasts are typically restricted to a LAN. Additional methods are required to build a WAN BACnet system.
Each LAN can include a BBMD that functions similar to BBMDs in IPv4–based BACnet/IP networks. This approach is most effective when multiple IT subnetworks exist in a building and multicasts are not configured to cross routers.
To reduce the complexity of BBMD configuration, or when a system must securely span the internet, BACnet Secure Connect (B/SC) with RC-RemoteAccess from Reliable Controls is a cost-effective and secure alternative.
BACnet/IPv6 network identification: Multicast domains
In BACnet/IP networks, each network segment is identified by the IP subnet and the UDP port assigned to the BACnet/IP network number. In BACnet/IPv6 networks, each segment is identified a multicast scope address, such as FF02::BAC0, along with an assigned UDP port.
UDP ports can use the same range as BACnet/IP networks. The following example shows recommended network values:
RC host: 1
BACnet device instance: 1000
BACnet/IPv6 network number: 161
BACnet/IPv6 scope address: FF02::BAC0
BACnet/IPv6 UPD port: 30161
RC-Studio and RC-WebView software from Reliable Controls support IPv6, which introduces new ways to structure, secure, and scale your building automation networks. Understanding how it works today helps you design systems that are ready for the future.
