How is friction a non-conservative force?

A force is said to be non-conservative,if work done by or against the force in moving a body from one position to another,depends on the path followed between these two positions.
Friction is the most common non-conservative force.If a body is moved from aposition A to another position B on a rough table,work done against frictional force shall depend on the length of the path between A and B and not only on these two positions.
Futher if body is brought back to its initial position A,work has to be done against the frictional forces,which opposes the motion always.Hence net work done against the frictional forces in moving a body over a round trip is not zero.Thus friction is an non-conservative force.