When we give alternative ways of authentication (local & radius), cisco routers bypass the first method of local & go for radius if the user provided username is not in local database.
(aaa authentication login default local group radius)
But if first method is Radius , & user provides a username not available in radius server it shows as an authentication failure & doesn't check local database (aaa authentication login default group radius local )
Anyone can explain why does it treat as
local failure - username not in local database , if username is not in local database it checks radius
radius failure - radius server not available , username not in radius database is not a reason to bypass the radius & check local