Which IPv6 feature blocks traffic when the source address is not present in the device binding table?

IPv6 Source Guard is the correct answer because it enforces security by verifying the source IPv6 address of incoming packets against a binding table. If a packet's source address isn't found in this table, it's dropped, preventing spoofing and unauthorized traffic. IPv6 DAD Proxy assists in Duplicate Address Detection for hosts behind a router, not traffic filtering. IPv6 RA Guard protects against rogue Router Advertisements, preventing malicious devices from becoming default gateways. IPv6 Snooping (typically NDP Snooping) builds the binding table by inspecting Neighbor Discovery Protocol messages, but it doesn't directly block traffic based on that table; Source Guard uses the table built by snooping.