Programming IP/KNX-router

I dont know why it would be a problem. Normally it works.

You probably have a problem on the network. If everything works except the ETS-download, I would guess that the problem is related to the "IGMP Snooping". A feature of some switches for controlling multicast traffic. During the programming process the IP-router restarts. it might be that it terminates its IGMP membership which prevents further communication with ETS and you get a timeout.

This is just a guess, I would recommend that you use Wireshark to see what's happening on the network and then on both sides of the switch or router.

Learn more about IGMP snooping at Wikipedia

This answer is old but someone could stop here and don't be cleared enough.

It is not possible to program the IP device using the same IP device with ETS. You can in fact program an IP device, router or tunneling with other IP router or a USB device.

When you program a device a lot of telegrams are exchanged in the bus and the IP device would be busy making all that communication. When he reaches the point of confirming the values received it would make an error trying to use the new configuration because the previous one was in use.

IP router is using some kind of "virtual psychical address" which is called tunneling address, to use it as IP-interface (to communication) and IP-router (to routing, filtering etc).

Some example:

knx router: 1.1.0 knx tunneling addr: 1.1.253

If you are programming some device (for example 1.2.5), in telegram then sender address is 1.1.253, which is routed by 1.1.0 and 1.2.0 to 1.2.5. Acknowledge goes from 1.2.5 to the 1.1.253 - which is catched and interpretated by 1.1.0.

1.1.0 and 1.1.253 is the same device, which uses two addresses. Maybe sending telegrams to itself isn't possible, and the router could not ACK the transmition?