Displaying products for Rj11 Adaptors - from our range of leading brand manufacturers. Rj11 RJ45 Adaptors Enabling equipment with a RJ45 type plug to be used on RJ11 wiring systems that are now commonly used in offices and public buildings for Broadband . The most commonly used is the four-wire version listed here In the 568B color code, we need W/O-O/W (Pins 1&2) and W/G-G/W pairs (Pins 3&6) Pins 4, 5, 7, and 8 can be ignored (they are for PoE and Gigabit applications, which we are not going attempt with this type of cable). The answer is possibly... but without knowing more about the cable and the layout it is difficult to tell. For 10/100 Ethernet to work, you need to have a straight through connection of pins 1, 2, 3, and 6, and the other pins are not relevant/not used in this scenario.

RJ11 to RJ45 - Super User networking - Convert RJ11 to RJ45 - Super User

In theory, telephony cable can be used to support 10/100 connections (not Gigabit) over short distances. If you can find a telephony cable that is not cut and is a "home run" between the two points you need to connect, and it contains at least 4 conductors, it may be possible.