Which of the following technique involves scanning the headers of IP packets leaving a network to make sure that the unauthorized or malicious traffic never leaves the internal network?

Egress filtering is the practice of monitoring and potentially restricting the flow of traffic as it leaves a network. The primary purpose is to prevent unauthorized or malicious traffic from originating within the internal network and reaching external destinations. By inspecting outbound packet headers against a defined security policy, a firewall or router can block data exfiltration attempts, prevent internal hosts from participating in DDoS attacks, and stop the spread of malware.

B. Throttling is a technique to control the rate of traffic to manage bandwidth or prevent denial-of-service, not to inspect its legitimacy based on header content.
C. Rate limiting is functionally the same as throttling; it controls the frequency of packets or requests but does not involve policy-based inspection of traffic content.
D. Ingress filtering is the opposite of egress filtering. It involves scanning and filtering traffic as it enters a network from an external source.

National Institute of Standards and Technology (NIST), Special Publication 800-41 Rev. 1, "Guidelines on Firewalls and Firewall Policy", Section 4.3. This document discusses the importance of creating policies for both inbound (ingress) and outbound (egress) traffic filtering.

Ferguson, P., & Senie, D. (2000). "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing". RFC 2827. While focused on ingress filtering, this document's principles are foundational to traffic control at network boundaries, with egress filtering being the outbound counterpart.