Yes, a KNX IP router can handle both tunneling and routing at the same time. Most modern KNX IP routers support both functions simultaneously, meaning they can forward group telegrams across IP subnets while also accepting direct configuration or monitoring connections from engineering tools like ETS. The sections below explain how these two functions differ, what limits apply, and when a dedicated interface makes more sense.
What is the difference between KNX IP tunneling and KNX IP routing?
KNX IP tunneling and KNX IP routing are two distinct communication modes built into a KNX IP router, and they serve different purposes. Routing is the backbone function: it carries KNX group telegrams between different KNX line segments over an IP backbone, connecting areas and lines into one coherent installation. Tunneling creates a direct, point-to-point connection between a software client — such as ETS or a visualisation tool — and the KNX bus, as if that client were a physical device on the line.
In practical terms, routing is always running in the background, silently forwarding telegrams according to the filter table programmed into the router. Tunneling, by contrast, is an on-demand connection opened by a specific application that needs to read, write, or monitor the bus directly. The two modes use different mechanisms: routing relies on IP multicast, while tunneling uses unicast UDP connections to individual client addresses.
Understanding this distinction matters because the two modes compete for the same hardware resources — the KNX IP router — and each places different demands on its processing capacity.
Can a KNX IP router run tunneling and routing simultaneously?
Yes, a KNX IP router can run tunneling and routing simultaneously. The router continues to forward group telegrams across the IP backbone while maintaining one or more active tunnel connections. This is by design: the KNX specification allows a single device to fulfil both roles at once, which is why most installations rely on it without any special configuration.
That said, simultaneous operation does come with practical constraints. Every active tunnel connection consumes a slot in the router’s connection table and adds processing overhead. When a tunnel client sends or receives a high volume of telegrams — for example, during a full ETS download or a diagnostic scan — the router’s internal bus coupler handles two streams of traffic at once. In well-designed installations this rarely causes problems, but in large or heavily loaded systems it is worth monitoring.
The key takeaway is that simultaneous operation is supported and reliable for typical use cases, but the number of tunnel connections and the volume of tunnel traffic both have upper limits that affect overall behaviour.
How many tunnel connections does a KNX IP router support?
Most KNX IP routers support between one and four simultaneous tunnel connections, with four being the most common maximum in current devices. The exact number depends on the manufacturer and firmware version, so checking the device’s technical datasheet is always the right first step.
Each tunnel connection occupies one of these slots for as long as the client application keeps it open. Common clients include:
- ETS (for programming, commissioning, and diagnostics)
- Visualisation servers or home automation controllers
- Monitoring tools and bus analysers
- third-party KNX integration software solutions
If all available slots are occupied and a new client attempts to connect, the router will refuse the connection. This is a frequent source of confusion during commissioning: an engineer opens ETS, finds the router unreachable, and suspects a network problem — when in reality a visualisation server is holding an open tunnel connection in the background. Closing unused connections or restarting the client application usually resolves this immediately.
What happens to KNX routing when tunnel traffic is high?
When tunnel traffic is high, KNX routing continues to function but may experience increased latency or, in extreme cases, telegram loss. The router’s internal processor handles both routing and tunneling through the same bus coupler, so a sustained burst of tunnel telegrams — such as those generated during a full group address scan in ETS — can temporarily slow down the forwarding of routine group telegrams used by the live installation.
In practice, this effect is rarely noticeable in residential or small commercial installations because commissioning and live operation seldom overlap at peak load. In larger buildings with complex filter tables and many active group addresses, the impact can be more visible. Some higher-end KNX IP routers address this by prioritising routing traffic over tunneling traffic internally, but this behaviour is device-specific and not mandated by the KNX standard.
The practical advice is straightforward: avoid running intensive ETS operations — such as full downloads or bus scans — during periods when the installation is in active use, particularly in environments where lighting scenes, HVAC control, or access systems rely on fast telegram delivery.
When should you use a separate KNX IP interface instead?
A separate KNX IP interface is the right choice when tunneling is the primary or only requirement and you do not need IP backbone routing. A dedicated interface handles only tunnel connections, which means it does not compete with routing traffic and is simpler to configure. It is the standard tool for commissioning a single KNX line with ETS when no IP backbone is involved.
Consider a separate KNX IP interface in these situations:
- You are commissioning a single-line installation and need a clean, dedicated ETS connection
- All available tunnel slots on the IP router are regularly occupied by other clients
- You want to isolate diagnostic or monitoring traffic from the production routing infrastructure
- The router is located in a remote cabinet and a local interface provides easier physical access to the bus
In multi-line installations where an IP backbone already exists, the KNX IP router’s built-in tunnel support is usually sufficient. Adding a separate interface only makes sense when the router’s tunnel capacity becomes a genuine bottleneck or when operational separation between commissioning and live traffic is a priority.
How Xxter Supports KNX Professionals
For installers and integrators working with KNX systems daily, getting the infrastructure right — routers, tunneling, routing, and integration — is only part of the challenge. The other part is giving end users a reliable, intuitive way to interact with the installation they have built.
Xxter provides exactly that. The Xxter controller sits at the centre of any KNX installation and connects it to the free Xxter app, available on iOS, Android, Windows, and Apple Watch. For professionals, this means:
- A proven KNX controller that integrates with existing IP infrastructure without disrupting routing or tunneling behaviour
- Support for KNX alongside Modbus, BACnet, EnOcean, Art-Net DMX, and Philips Hue in a single platform
- Voice control via Apple HomeKit, Amazon Alexa, and Google Assistant through the Pairot bridge
- No license fees, no subscription costs, and no device limits on the Xxter app
Whether you are designing a new KNX installation or upgrading an existing one, Xxter’s KNX solutions give you a reliable foundation and a user experience your clients will appreciate from day one. Get in touch with the Xxter team to find out how the platform fits your next project.