Regarding VSAs, which statement is true?

A.
VSAs may be implemented on any RADIUS server.

B.
VSAs are proprietary, and therefore may only be used on the RADIUS server of that
vendor. For example, a Cisco VSA may only be used on a Cisco RADIUS server, such as
ACS or ISE.

C.
VSAs do not apply to RADIUS; they are a TACACS attribute.

D.
Each VSA is defined in an RFC and is considered to be a standard.