Final answer:
To generate an RSA key for SSH on a router, one must assign a DNS domain name to the router. This is crucial for forming a fully qualified domain name (FQDN), which is required to produce a proper RSA key pair for secure SSH communication.
Step-by-step explanation:
To generate an RSA key for SSH on a router, you need to assign a DNS domain name to the router. This step is necessary because RSA keys are tied to the hostname and the domain name of the device to form a fully qualified domain name (FQDN). Without a domain name, the router cannot generate a proper RSA key pair which is essential for enabling SSH for secure management access.
Other prerequisite configurations, such as enabling SSH and configuring VTY (Virtual Terminal Lines) access, are important for setting up SSH on the router but are not directly involved in the generation of the RSA key pair. Creating a user with a password is necessary for authentication purposes once SSH has been set up and is not specifically for RSA key generation.