Radius-Server Command Not Available in Cisco

RADIUS support was introduced in 11.3T and for using radius-server host x.x.x.x …. command you need to enable the AAA new model with aaa new-model command in the global configuration mode, after that you are able to use radius-server host x.x.x.x …. command in your Cisco switches

Switch2950(config)#aaa new-model