Security - privilege levels and enable keyword

Cisco IOS devices can be configured to use usernames and passwords to protect unauthorized connectivity to the CLI. Each username can be associated with a privilege level between 0 and 15.

When employing a privilege level of 15 using the local user database, this bypasses any use of the enable mechanism. Privilege level 15 is actually called privileged EXEC mode which is the mode you enter when you enter the enable keyword and the appropriate password. This means that such a user does not need to enter the enable command to enter privileged EXEC mode but is already placed in that mode.

This can be seen in the following example where a user is logging into an IOS device using Telnet:

R2#telnet 192.168.12.1
Trying 192.168.12.1 ... Open

User Access Verification

Username: admin
Password: 
R1#

Notice the "#" in the prompt which indicates privileged EXEC mode.

Links:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/security/configuration_guide/b_sec_3se_3850_cg/b_sec_3se_3850_cg_chapter_011.pdf

https://forum.networklessons.com/t/how-to-install-tacacs-on-linux-centos/1010/38?u=lagapides