I finally removed the router I received from my ISP, Sunrise (Switzerland), which was in front of my Omnia Turris. Now I am able to connect directly via Omnia Turris and its SFP port to the fiber/internet. Since the Sunrise support was of little help during the switching I would like to write down how to configure the interface for other users who might have the same issue.
SFP module (provided by Sunrise)
Was actually straight forward, the only info missing was the vlan id which is
10 (as found in this forum) by which all packets have to be tagged. Here is explained how to adapt the physical interface accordingly. Following an excerpt of my
config interface 'wan' option proto 'dhcp' option ifname 'eth1.10'
That’s it, hope it helps