Its available on all newer software versions of ios you shouldn't have an issue 2k,3k,4k,6k series switches , its even on 2ks now in nx-os and in 9ks lldp has replaced cdp completely
If you need to check a specific version you can see what it supports on feature navigator or check its syntax command guide sheet on Cisco website
http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp
