# Unavailability of TACACS+ Services During Unified ISSU

During the upgrade phase of unified ISSU, TACACS+ services are unavailable. If you have configured AAA authentication for Telnet (with the aaa new-model command) this lack of availability affects CLI authentication, authorization, and accounting activities.

CLI login and privilege authentication cannot succeed during a unified ISSU unless you configure at least one of the alternate authentication methods with the aaa authentication login command: enable, line, or none.

Similarly, CLI exec and command authorization cannot succeed during a unified ISSU unless you configure one of the alternate authorization methods with the aaa authorization command: if-authenticated or none.

Because there is no alternate method of accounting other than TACACS, CLI exec and command accounting does not work during this phase.

#### Related Topics

- Application Support for Unified ISSU