How to find even and odd eigenmodes using CST eigenmode solver or by other means

Hi,
I was trying to find the modes of a symmetric photonic crystal based waveguide. The eigenmode solver of CST is doing nice with my requirement but in many publication people are getting even and odd modes within the band gap for a symmetrical structure.

I am a bit confused that, do I have to do something to get both the modes or it is the job of that software which automatically produce these modes if they both exist at all.

I've not used CST, but in HFSS its the job of the software. You just have to tell it to search for more modes.