How do you secure VTY (virtual terminal) lines for remote access?

Enter line vty 0 15, set password <pw>, then login; VTY lines (0-15, 16 total) carry Telnet/SSH and deny access by default until configured.

Switch(config)# line vty 0 15
Switch(config-line)# password cisco
Switch(config-line)# login
Switch(config-line)# end

Key points:

• VTY lines enable remote access via Telnet or SSH
• Most Cisco switches support 16 VTY lines (numbered 0 to 15)
• The login command is required to enforce password checking
• Without a VTY password configured, remote access is denied by default

Go deeper:

• Jeremy's IT Lab — SSH (CCNA Day 42) — secures the VTY lines and enables SSH on them.
• Secure Shell (Wikipedia) — the protocol the VTY lines should carry instead of Telnet.