Hello,
I’m still in the planning process and I’m trying to understand what kind of KNX/IP gateway would be better suited to my installation.
Given that the only reason why I need such a device is to use OH3 to control KNX devices (I don’t need any line/area coupling as the bus topology is very simple) is there any reason why I should spend double the money to buy a KNX Router instead of a KNX Interface (Tunnel)?
Thanks
For me tunneling never worked reliably. Since I use routing no issues.
As you already said, normally an interface would do for your use case. A router only adds the possibility to act as a line coupler.
But as Jan also noted, some interfaces simply do not work in either or the other mode. I guess this is due to the problem, that this kind of IoT devices are build with a handmade and optimized IP stack and KNX implementations. I tried once to implement an own IP device and I can tell you, the KNX specification on that is really complex.
With a router you simply add and option, if tunnel does not work. Your strategy here could also be, buy and try several IP Interfaces from different vendors and send back those who will not work in tunnel mode.
From the configuration point of view a router is much more easier to configure, because for finding and negotiating the connection between the interface and a client (the openHAB bridge), they use IP multicast on a default network address. So basically saying, that you use router mode, is enough to get it working. So there is no need to configure endpoint addresses or other communication parameters for the ip interface or openHAB side.
Like Jan, I also only used router mode ever and it always worked.
Router mode is “reliable” because of the UDP connection using multicast, but the risk of losing some packets exists.
With the tunnel mode the connection is of TCP type, point to point, unicast. The problems that can exist are solely with the interface equipment (it can block or drop the connection). Some interfaces have multiple tunneling connections and this is useful when you want to have simultaneous parallel connections (e.g. openHAB and ETS at the same time).
A few years ago I asked me the same question. At the end I decided to buy a Weinzierl KNX interface and not a router. Mainly because I was not sure if multicast connections needed a network switch supporting them and if this would cause problems.
I am using the Interface for openHAB and for connections by the ETS and booth works without any problems. Before that I used a Wiregate server to connect openHAB to the KNX buy, this too worked very well. I also tried using the Timberwolf server, kind of a successor to the Wiregate, this too worked without problems.
So there are lot of options 
Thank you everyone for giving your feedback, this is very appreciated.
@franks @george.erhan So, as I understand, you’re saying that I can go with a “simple” interface just acting as a Tunnel, but I could potentially face some issues due to “bad” implementation of the KNXnet/IP protocol on the interface itself. Am I right?
That’s a bit weird to me (not what you’re writing, that of course makes perfectly sense, but the fact that a vendor sells a device made specifically for a single task and that device has problems handling that task…that’s a nonsense to me…how could such a device even get the KNX certification?)
I understand that a Router might be easier to configure, since basically there’s nothing to configure as long as you are fine to use the default multicast addressing, but I wouldn’t say that UDP is more reliable, as it is indeed very prone to packet loss (I guess that’s why you put quotes around that word) given that it is a connectionless protocol.