This will show the settings required to have the FritzBox own a /29 subnet and allow a dedicated firewall device to own the other five IP addresses.
Other Internet Service ProviderConnection to a DSL lineYes. Username (if using Zen Internet) = zen123456@zenMaintain Permanently (recommended for flat rates). Do not tick Delay disconnection by provider to the period betweenUse VLAN for Internet access101Set manually with VPI = 1, VCI = 32 and Encapsulation = PPPoEConnected network devices are also allowed to establish their own Internet connections (not recommended)Enter the IP address manuallyThis information is sources from this link
This information is sourced from this link.
Log onto Fritz!box UI and go to the Top Right corner and enable the Advanced View option.
Then go to INTERNET > DSL Information and set Annex to B, if based in UK and Using VDSL (FTTC) or Annex A if you are using ADSL and ADSL+ (unsure if needed, but did it just to be sure).
Then go to INTERNET > ACCOUNT INFORMATION and select
Then Select PPPoE Passthrough and check the 'Connected Devices are also allowed to their own Internet connection' box.
Do not forget to disable the 2.4GHz and 5Ghz wifi and I use LAN1 for the connection from Modem (Fritz!Box) to existing Router (WAN Port)
Hope this proves a good use for the Fritz!Box 3490, as it does use the Lantiq (XWAY VRX288) xDSL chipset and works a treat on both ECI and Huawei DSLAMS in the UK