It depends on the standard.
Generally there is no RJ-11 to RJ-45 "standard". Otherwise it would no longer be a standard. That's like saying what is the standard for standardized apples to standardized oranges?
RJ-11 is not a standard for ethernet. It will work, but I want to strangle the people that did this. Makes me thing you aren't really getting ethernet in the room.
And before anybody pounces - sure the RJ-11 pinout was later included into RJ-45 connector, but that is a hole-nutter thread.