2m RJ11 to RJ45 Cable Ethernet Modem Data Telephone ASDL Patch Lead Broadband High Speed BT Internet Plug 6P4C to 8P8C Flat Network Extension Cord Compatible with Modem, Router, Landline Wire (White)
RJ11 to RJ45 Modem Cable 2m black
What is a method to connect an RJ11 cable into an RJ45 router? - Quora