Even though the Flat Layer approach reduces the authentication delay as well as avoids single point of failure, it has some disadvantages. The first disadvantage is scalability problem. As we said before, each RADIUS server must know the information of all other RADIUS servers present in the system. If a new RADIUS server joins or leaves, all RADIUS servers need to update their information. If there are a large number of RADIUS servers in system, the cost of updating information is very big.