The title of this message is somewhat confusing :)
Am i right in presuming that you are using A VLAN trunk to the switch from the internal interface? and that you are NOT using the DMZ interface, but instead an VLan subinterface?
On that presumption, then you will need to have the internal interface also assigned a vlan ID as well as the DMZ sub interface. then routing between the two will work, as long as you have rules to allow it.
So if you are trying to connect from internal vlan1 to DMZ vlan2 for example, then you will need have firewall rules to allow it, so an INT -> DMZ allow and a DMZ -> INT for the other direction.
But, its unusual to have a core switch on the DMZ... and if its a true DMZ, then you wouldnt want any DMZ -> INTERNAL traffic allowed.
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