@reap @AdmiralAckbar73 @ChuckPa @preacha @xLuchs
I solved it. Guys… really. It’s working again.
This is a combination of multiple factors. If:
- you are using AVM FritzBox 6591 or 6660 and
- using any new Vodafone subscription which involves DOCSIS 3.1 and
- have a FritzOs which is quite new (>7.10 or so)
this problem hits you.
The solution is quite “easy” if you know what happens and I stumbled uppon this solution by accident.
I tried to capture the network stream between my host machine and the internet via FritzBox and usually there is a button for that which outputs you the . cap File (anyone remember?).
Since a few FritzOS upgrades this buttons dissapeared to an unknown menu 
but nevertheless I found it :
Guess what? It won’t work with my AVM 6660 - its too new and the buttons all do not work to capture any traffic.
But the journey was not useless… please guys. Scroll down a little bit in the last screen:
It’s called “Paketbeschleunigung” (Packet Acceleration). Disable “Hardware Beschleunigung” - and you are done. This is it.
I think there is something missing in the AVM implementation of DOCSIS 3.1 in combination with that hardware acceleration.
I have not found more information about that acceleration but a topic here: Was genau macht Paket-Beschleunigung und Hardwarebeschleunigung? | IP Phone Forum and some sentences remind me of what @ChuckPa told me
…da werden dann IP-Adressen und auch -Ports umgeschrieben bei portbasierten Protokollen und ebenso die “L2-Adressen” (aka MAC-Adressen), die ebenfalls passen müssen, damit das richtige Ziel im LAN dieses Paket überhaupt erst erhält…
Wait what? L2 adresses, MAC filtering bla bla?
→ directly disabled the acceleration and it worked for me.
… too much magic ain’t good …
Man, what a pain in the ass !
