# Symmetry factor of Feynman diagram

What is the symmetry factor for the following Feynman diagram if we assume that the external points are held fixed?

Please ignore the arrows in the diagram. I am referring to the second diagram on the third row of Figure 9.7, page 62, of Srednicki's book, but, in contrast to Srednicki, I want the external points to be held fixed.

• Apart from swapping the propagators in the loop in the upper part of the diagram, are we also allowed to swap the two vertices in the loop in the upper part of the diagram, giving us a symmetry factor of $4$? – user127054 Jun 21 '14 at 12:16