Question 650
Two branches establish IKE security associations but pass no traffic after a new upstream address-translating router is installed. Which Cisco security control or operational response BEST addresses the stated need?
Explanation
Correct Answer
Use negotiated IKE/IPsec proposals with matching identities and selectors, and enable appropriate UDP encapsulation when NAT disrupts ESP carriage. This control addresses the failure mechanism and narrows the enforcement boundary. NAT traversal commonly encapsulates ESP over UDP 4500; a successful IKE handshake alone does not prove data-plane IPsec traffic passes. Confirm pre-change conditions using: Inspect IKE proposal mismatches, pre-shared or certificate identity, UDP 500 or 4500 reachability, NAT detection, and phase negotiation logs. Situation: Two branches establish IKE security associations but pass no traffic after a new upstream address-translating router is installed.
Incorrect Answers
Use cryptographic hashes for integrity, authenticated key exchange for confidentiality, and maintain a migration inventory for post-quantum risks. This response applies to Cryptographic hashes and post-quantum planning, not the controlling requirement in this case. A bare hash does not provide secrecy; post-quantum preparation requires crypto-agility planning rather than claiming traditional algorithms are already future-proof. For this scenario, the targeted action is: Use negotiated IKE/IPsec proposals with matching identities and selectors, and enable appropriate UDP encapsulation when NAT disrupts ESP carriage. Situation: Two branches establish IKE security associations but pass no traffic after a new upstream address-translating router is installed.
Choose route-based IPsec tunnels when dynamic routed topologies need predictable overlay interfaces and matched security policies. This response applies to Route-based versus policy-based VPN design, not the controlling requirement in this case. Route-based VPN separates routing decisions from the cryptographic tunnel interface whereas policy-based VPN relies on matching crypto traffic definitions. For this scenario, the targeted action is: Use negotiated IKE/IPsec proposals with matching identities and selectors, and enable appropriate UDP encapsulation when NAT disrupts ESP carriage. Situation: Two branches establish IKE security associations but pass no traffic after a new upstream address-translating router is installed.
Curate indicators with source confidence, freshness, context, and expiration before distributing to enforcement and investigation tools. This response applies to Threat intelligence indicator lifecycle, not the controlling requirement in this case. Threat indicators are leads with changing confidence, not immutable proof that every matching host is compromised. For this scenario, the targeted action is: Use negotiated IKE/IPsec proposals with matching identities and selectors, and enable appropriate UDP encapsulation when NAT disrupts ESP carriage. Situation: Two branches establish IKE security associations but pass no traffic after a new upstream address-translating router is installed.


