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Global ConfigDomain 5.0
ip domain-name [domain]
Assigns a default DNS domain to the router. While useful for resolving hostnames without typing a full suffix, its absolute primary purpose in CCNA labs is acting as a mandatory prerequisite for generating SSH cryptographic keys.
Quick Reference
Execution Mode
Router(config)#Target ApplicationSSH / DNS Resolution
Companion Prerequisite
hostname [name]Negation Command
no ip domain-nameCCNA Exam Gotchas
[!]
The FQDN Equation
When you run crypto key generate rsa, the router builds the mathematical label for the certificate by combining the Hostname and the Domain Name to create a Fully Qualified Domain Name (FQDN).
If the hostname is R1 and the domain is cisco.com, the key name becomes R1.cisco.com. If either variable is missing, the IOS throws an error and refuses to generate the keys.