4.19.1.1. Protocol elements

During the authentication process the participants use the following protocol elements:

  • REQUEST: When a new connection attempt arrives to the NAS, it sends a message towards the RADIUS server requesting the authentication of the user; or it sends an accounting related message.

  • RESPONSE: The RADIUS server attempts to authenticate the user when an authentication REQUEST is received. The server returns the result of the process to the NAS in a RESPONSE message.

  • ATTRIBUTE: Both the REQUEST and RESPONSE packets contain a set of structured attribute-value pairs containing information like username, password or the type of service requested by the user. Attributes are identified by a number ranging from 0 to 255. Each attribute has an associated type specified in the RADIUS RFCs which define the range of valid values.

    Note

    There are also some vendor-specific RADIUS dictionaries, where certain attributes are used for internal purposes. Obviously, these are not discussed in the RFCs.