Cisco Certified Internetwork Expert (CCIE) Practice Test

When applying MD5 route authentication on routers running RIP or EIGRP, which two important key chain considerations should be accounted for? (Choose two)

1. Key 0 of all key chains must match for all routers in the autonomous system

2. No more than three keys should be configured in any single chain

3. Routers should be configured for NTP to synchronize their clocks

4. The lifetimes of the keys in the chain should overlap

The correct answer is: Routers should be configured for NTP to synchronize their clocks

When implementing MD5 route authentication on routers using RIP or EIGRP, it is essential to ensure time synchronization across devices. Configuring routers with NTP (Network Time Protocol) is critical because the timestamps used in the key chain authentication process rely on accurate time settings. If the clocks aren't synchronized, key changes may not be recognized correctly, leading to rejected messages and potential authentication failures. Accurate timestamps help ensure that only valid keys within their defined lifetimes are used for authenticating routing updates. If there is a mismatch in time, even if keys are valid, the authentication process may erroneously fail due to perceived discrepancies. Thus, having NTP configured supports the integrity and functionality of the routing authentication mechanism. Considering the other options, while the lifetime of keys should indeed be managed carefully, not overlapping their lifetimes would only serve to enhance security by preventing old keys from being accepted after a new key becomes active. However, significant emphasis should be placed on time synchronization to ensure the reliability of the authentication process in real-time operations.