How IP DHCP Snooping works, trusted & untrusted ports, DHCP Snooping Binding Database, Cisco Catalyst & Nexus Licensing & Features, DHCP Snooping Option-82 Data Insertion. Preventing DHCP attacks and more. Catalyst Nexus switching supporting DHCP Snooping.
http://www.firewall.cx/cisco-technical-knowledgebase/cisco-switches/1215-understanding-dhcp-snooping-concepts-and-how-it-works.html