Hallo, es tut mir leid, mein Deutsch ist nicht sehr gut. Also, um Verwirrung zu vermeiden, werde ich in Englisch schreiben.

My Speedport Smart 3 router upgraded to the new firmware 010137.4.6.001.2.

https://www.telekom.de/hilfe/geraete-zubehoer/router/speedport-smart-3/firmware-speedport-smart-3?samChecked=true.

My set up is Router (192.168.2.1) >> internal router (192.168.1.1) >> multiple devices.

I had no issues until last week, where I decided to reset my router because of forgotten settings.  Of course, the DHCP tables were cleaned, because of the reset.  After the reset, and configuration, I could not connect to the internet.  I was connected directly to the router, and nothing worked.  When I went to the router web 192.168.2.1 (default), I saw that the no device was shown with DHCP lease, and in the logs, it said DHCP assignment had failed.  I looked at the auto-IP configuration on my computer, and it picked up 192.168.1.xxx IP, with Gateway and DNS at 192.168.1.1.  This is odd because my internal network where I have medias, raspberryPi, and other devices directly connected runs on 192.168.1.1.  I checked the TV box connected to the router, and it also had 192.168.1.xxy IP with error that it couldn't connect to TV service, so looked like router was handing out different DHCP IP vs. its own, and computers didn't know how to get through.  

I manually changed my computer configuration to 192.168.2.xxx, changed Gateway and DNS, and internet was working.  I removed the manual configuration and it was back to same. I changed the DHCP assignment from 192.168.2.x to 192.168.1.x on the Speedport, and with auto-configuration on my computer, again I had internet.

So, this caused a huge problem/headache for my internal network because most of my internal network is static IP and it wasn't going to work with my internal router being 192.168.1.1 and Speedport also being same IP.  I had to re-do my internal network to change the devices IP and it wasted my entire day.

Something I noticed that, it didn't crash immediately after the firmware update.  I have 3 devices connected to Speedport.  TV, Internal Router, and a Server.  They all were assigned static IP via the Speedport page > Network > Connected Devices > "Always same IP Address" for each device.  So, they were receiving same IP, so I had no issues because no new devices were plugged in. Until, after the reset, which cleaned out the table and router started to hand out different IP than the DHCP allowed.

I am not sure if it is just me (odd), or someone else has run into this, or someone else will run into this in the future.  I believe it is an issue on the firmware, but if I have overlooked something, please tell me. 

Sorry for long text.

Thank you

Reds