When RADIUS servers are not reachable, the router falls back to the local database for authentication. In the provided configuration, there are two methods defined under aaa authentication login. The first method list group1 uses the local database where a username is not specified but a password is set to "cisco123". The second method list group2 specifies the use of RADIUS (group radius) and if that fails, it falls back to local (local). Since RADIUS is not reachable in this scenario, we refer to the local database which does not require a username but requires the password "cisco123".