What are the guidelines for naming a Cisco device (hostname)?

Start with a letter, end with a letter or digit, use only letters/digits/dashes, no spaces, and keep it under 64 characters.

Device naming guidelines:

• Start with a letter
• Contain no spaces
• End with a letter or digit
• Use only letters, digits, and dashes
• Be less than 64 characters in length

Command to set hostname:

Switch(config)# hostname Sw-Floor-1
Sw-Floor-1(config)#

Note: Use no hostname to return to the default name.

Go deeper:

• Cisco IOS (Wikipedia) — the global-config layer where hostname and other device-identity commands live.