What command sets the authentication method for VRRP to plaintext with the key string 'Cisco123'?

The command that effectively sets the authentication method for VRRP to plaintext using the key string 'Cisco123' is structured as follows: 'vrrp 1 authentication text Cisco123'. In this command, 'vrrp 1' indicates the VRRP group ID, and 'authentication text' specifies that plaintext authentication with a key is being used. Following this, the actual key string 'Cisco123' is provided.

This command tells the router to utilize simple plaintext authentication for the specified VRRP group, which is essential for ensuring that only routers with the correct key can participate in the VRRP instance. Understanding this command structure is crucial for anyone configuring VRRP, as it involves controlling how routers communicate and authenticate each other in a redundant configuration.

Other options either use incorrect command formats or terms that do not exist in VRRP configurations, which is why they would not effectively set the authentication method.