Currently, there are two pre-requisite options for the CCSP certification.
1) CCNA Security certification will fulfill the CCSP pre-requisite requirement.
2) If you already have a valid CCNA certification + valid SND exam, then this will also fulfill the CCSP pre-requisite requirement (Note: The SND exam was retired on 17-Nov-2008 and is no longer available. However, it is still valid for exactly 3 years for the individuals who passed it before its retired date)
Also, having a valid CCIE certification can act as a pre-requisite for the CCSP.