What is the cause of the authentication failure with neighbor 10.1.1.4?
- The authentication key string does not match
- The EIGRP AS number does not match
- The K-values do not match
- The hello interval is misconfigured
Explanation: According to the sources, an authentication failure between EIGRP neighbors occurs when the configured security parameters do not match .
Specifically, if the authentication key IDs or the key strings (passwords) are inconsistent between peers, the router will ignore the incoming EIGRP packets and trigger a syslog message such as Auth failure or a debug message stating invalid authentication .
While other factors like mismatched AS numbers or K-values will also prevent a neighbor relationship from forming, they are associated with different troubleshooting symptoms, and hello intervals are not required to match for EIGRP adjacency to be successfully established .
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