It is indeed feasible to link two routers to one fiber modem and this arrangement can be advantageous, especially in cases of a multi-storeyed residence requiring more WiFi coverage or additional wired connectivity options. Assume you have house with direct access to an optic fibre cable (FTTP). In the basement, there is the ONT+residental gateway device that converts the light impulses to Ethernet. This setup has to be changed because the house will be. The easiest way to do is, terminate your ISP connection to single router with at least 2 independent LAN interfaces, then you can build 2 separate networks there. However the real problem is how to create a balance, so assume room A is torrenting and taking up 90% of your internet bandwidth, then. Are all the strands in the optic fiber cable gonna work at the same time and are they compatible with the transceivers? Thank you yes, for single-mode modules, you'll need single mode fiber/cable.
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