Why the ER605 ?
The Raspi with Pihole can be connected directly to the IB4. It has been working for me for >4 years without any problems.
See https://community.swisscom.ch/d/651749-pi-hole-und-was-du-dazu-wissen-musst
….keep on rockin'
POGO 1104 same here, plugged the Raspi into the housing of a TV box and connected it directly to the router.
PiHole and Unbound (own DNS server) are running there.
I used the following instructions to set it up: https://www.crosstalksolutions.com/the-worlds-greatest-pi-hole-and-unbound-tutorial-2023/
(External links at your own risk…)
Ich bin ein als Privatkunde getarnter Swisscom-Mitarbeiter im Bereich Service Continuity.