1-5Table 1-1 Main values of the Code fieldCode Packet type Description1 Access-RequestFrom the client to the server. A packet of this typecarries user information for the server toauthenticate the user. It must contain theUser-Name attribute and can optionally contain theattributes of NAS-IP-Address, User-Password,and NAS-Port.2 Access-AcceptFrom the server to the client. If all the attributevalues carried in the Access-Request areacceptable, that is, the authentication succeeds,the server sends an Access-Accept response.3 Access-RejectFrom the server to the client. If any attribute valuecarried in the Access-Request is unacceptable, theserver rejects the user and sends anAccess-Reject response.4 Accounting-RequestFrom the client to the server. A packet of this typecarries user information for the server to start/stopaccounting for the user. It contains theAcct-Status-Type attribute, which indicateswhether the server is requested to start theaccounting or to end the accounting.5 Accounting-ResponseFrom the server to the client. The server sends tothe client a packet of this type to notify that it hasreceived the Accounting-Request and hascorrectly started recording the accountinginformation.3) The Identifier field (1-byte long) is for matching request packets and response packets anddetecting retransmitted request packets. The request and response packets of the same type havethe same identifier.4) The Length field (2-byte long) indicates the length of the entire packet, including the Code,Identifier, Length, Authenticator, and Attribute fields. The value of the field is in the range 20 to4096. Bytes beyond the length are considered the padding and are neglected upon reception. If thelength of a received packet is less than that indicated by the Length field, the packet is dropped.5) The Authenticator field (16-byte long) is used to authenticate replies from the RADIUS server, andis also used in the password hiding algorithm. There are two kinds of authenticators: requestauthenticator and response authenticator.6) The Attribute field, with a variable length, carries the specific authentication, authorization, andaccounting information for defining configuration details of the request or response. This field isrepresented in triplets of Type, Length, and Value.z Type: One byte, in the range 1 to 255. It indicates the type of the attribute. Commonly usedattributes for RADIUS authentication, authorization and accounting are listed in Table 1-2.z Length: One byte for indicating the length of the attribute in bytes, including the Type, Length, andValue fields.z Value: Value of the attribute, up to 253 bytes. Its format and content depend on the Type andLength fields.
