Question: Which of the following authentication mechanisms is vulnerable to an attacker spoofing source IP address and port, making it weaker than SIP Digest proxy-authentication in such scenarios?
Option 1: TLS (Transport Layer Security)
Option 2: SIP Digest with TCP
Option 3: IMS AKA (Authentication and Key Agreement) with IPsec
Option 4: IP Address Check Mechanism
Explanation: The IP Address Check Mechanism relies on verifying the source IP address and port to authenticate non-registration messages. If an attacker can spoof these, they can impersonate another user, breaking this mechanism's security. This vulnerability is explicitly mentioned as a weakness of the IP Address Check Mechanism compared to SIP Digest proxy-authentication, which remains secure against attackers capable only of spoofing source IP addresses and ports.