Is every Switch capable of Network Access Server? i am learning about Radius Server and particularly freeRadius. NAS devices are responsible for sending Authentication requests to the Radius Server. NAS devices include like Switch, wireless access points, DSLM. My question is Every Switch(different manufacturers) capable of NAS.

No, not all switches support it.

As you may have learned already this is part of the IEEE 802.1x standard , so the devices that support it are those who list `802.1X` as a supported feature.