The Identifier field (1 byte long) is used to match request packets and response packets and to
detect duplicate request packets. Request and response packets of the same type have the same
The Length field (2 byte long) indicates the length of the entire packet, including the Code,
Identifier, Length, Authenticator, and Attribute fields. Bytes beyond this length are considered padding
and are neglected upon reception. If the length of a received packet is less than this length, the packet
is dropped. The value of this field is in the range 20 to 4096.
The Authenticator field (16 byte long) is used to authenticate replies from the RADIUS server and
to encrypt user passwords. There are two types of authenticators: request authenticator and response
The Attributes field, variable in length, carries the specific authentication, authorization, and
accounting information that defines the configuration details of the request or response. This field may
contain multiple attributes, each with three sub-fields: Type, Length, and Value.
Type (1 byte long)—Indicates the type of the attribute. It is in the range 1 to 255. Commonly used
attributes for RADIUS authentication, authorization and accounting are listed in 3.
Length (1 byte long)—Indicates the length of the attribute in bytes, including the Type, Length, and
Value (up to 253 bytes)—Value of the attribute. Its format and content depend on the Type and Length