*sigh*
Ok, another approach: I figured out that the FritzBox requires a "VLAN ID" (provided by my provider) to make the internet running. This is three digit number. I never heard about VLAN's in that context.
Unfortunately I cannot find a documentation or forum thread that describes how to configure then internet access with having the providers VLAN ID only.
Is there a way to do so?
What I have tried: I added a VLAN with the given VLAN ID to Ether1 (WAN Port, attached to the ONT). But that does not change anything. Here is the current configuration:
[admin@RouterOS] >> export hide-sensitive
# jan/05/1970 04:39:28 by RouterOS 6.48.6
# software id = QXQC-WMAZ
#
# model = RB760iGS
# serial number = HD2086154BV
/interface bridge
add admin-mac=18:FD:74:8B:4F:B0 auto-mac=no comment=defconf name=bridge
/interface vlan
add interface=ether1 name=vlan1 vlan-id=132
/interface list
add comment=defconf name=WAN
add comment=defconf name=LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/ip pool
add name=default-dhcp ranges=192.168.88.10-192.168.88.254
/ip dhcp-server
add address-pool=default-dhcp disabled=no interface=bridge name=defconf
/interface bridge port
add bridge=bridge comment=defconf interface=ether2
add bridge=bridge comment=defconf interface=ether3
add bridge=bridge comment=defconf interface=ether4
add bridge=bridge comment=defconf interface=ether5
add bridge=bridge comment=defconf interface=sfp1
/ip neighbor discovery-settings
set discover-interface-list=LAN
/interface list member
add comment=defconf interface=bridge list=LAN
add comment=defconf interface=ether1 list=WAN
/ip address
add address=192.168.88.1/24 comment=defconf interface=bridge network=192.168.88.0
/ip dhcp-client
add comment=defconf disabled=no interface=ether1
/ip dhcp-server network
add address=192.168.88.0/24 comment=defconf gateway=192.168.88.1
/ip dns
set allow-remote-requests=yes
/ip dns static
add address=192.168.88.1 comment=defconf name=router.lan
/ip firewall filter
add action=accept chain=input comment="defconf: accept established,related,untracked" connection-state=established,related,untracked
add action=drop chain=input comment="defconf: drop invalid" connection-state=invalid
add action=accept chain=input comment="defconf: accept ICMP" protocol=icmp
add action=accept chain=input comment="defconf: accept to local loopback (for CAPsMAN)" dst-address=127.0.0.1
add action=drop chain=input comment="defconf: drop all not coming from LAN" in-interface-list=!LAN
add action=accept chain=forward comment="defconf: accept in ipsec policy" ipsec-policy=in,ipsec
add action=accept chain=forward comment="defconf: accept out ipsec policy" ipsec-policy=out,ipsec
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" connection-state=established,related
add action=accept chain=forward comment="defconf: accept established,related, untracked" connection-state=established,related,untracked
add action=drop chain=forward comment="defconf: drop invalid" connection-state=invalid
add action=drop chain=forward comment="defconf: drop all from WAN not DSTNATed" connection-nat-state=!dstnat connection-state=new in-interface-list=WAN
/ip firewall nat
add action=masquerade chain=srcnat comment="defconf: masquerade" ipsec-policy=out,none out-interface-list=WAN
/system identity
set name=RouterOS
/tool mac-server
set allowed-interface-list=LAN
/tool mac-server mac-winbox
set allowed-interface-list=LAN
Out of curiosity: How to access the exported data if I saved it to a file? I had to omit the file name in the end of the export command to print the output. Since there are no linux tools like "ls" or "cat", I dont know how to find the file.