Comment by bkor

> So, I find that it's highly unlikely that the ISP is officially required to support a user supplied modem, although I haven't consulted the EU laws on this.

Ziggo (called UPC in other EU countries) uses DOCSIS. The instructions on how to use your own DOCSIS modem are at the following link (in Dutch): https://www.ziggo.nl/klantenservice/apparaten/wifi-modems/ei...

Edit: it really is using your own modem. It's not about putting it in bridge mode.