The ability to inject packets into the Internet with a false source address is…

Answer: IP spoofing

Explanation: IP spoofing is the practice of sending network packets with a forged source IP address. The attacker alters the source address field so that the packet appears to come from a different host.

• Common uses: hiding the sender's identity, impersonating another host, enabling reflection/amplification attacks in DDoS campaigns.

• Limitations: forging the source IP does not guarantee the attacker can receive replies unless additional techniques (like on-path control or proxying) are used.

Why the other terms do not match:

• Man-in-the-middle attack involves intercepting and possibly altering communications between two parties; it centers on interception rather than simply forging source addresses.

• Phishing refers to social-engineering techniques to trick users into revealing information; it is not about forging packet source IPs.

• IP sniffing is passive traffic capture and analysis; it does not involve sending packets with fake source addresses.

Mitigation tips:

• Implement ingress and egress filtering and Unicast RPF to block packets with spoofed source addresses.

• Use authentication at the network or application layer (for example, IPsec) so that endpoints verify identities beyond IP addresses.

• Configure routers and rate limits to reduce the impact of reflection/amplification attacks that rely on spoofed source IPs.