4
RADIUS packet format
RADIUS uses UDP to transmit messages. It ensures smooth message exchange between the RADIUS
server and the client through a series of mechanisms, including the timer management mechanism, the
retransmission mechanism, and the backup server mechanism.
shows the RADIUS packet
format.
Figure 4
RADIUS packet format
Descriptions of the fields are as follows:
1.
The Code field (1 byte long) indicates the type of the RADIUS packet.
gives the possible
values and their meanings.
Table 1
Main values of the Code field
Code Packet
type Description
1 Access-Request
From the client to the server. A packet of this type carries user
information for the server to authenticate the user. It must
contain the User-Name attribute and can optionally contain the
attributes of NAS-IP-Address, User-Password, and NAS-Port.
2 Access-Accept
From the server to the client. If all the attribute values carried in
the Access-Request are acceptable, the authentication
succeeds, and the server sends an Access-Accept response.
3 Access-Reject
From the server to the client. If any attribute value carried in
the Access-Request is unacceptable, the authentication fails,
and the server sends an Access-Reject response.
4 Accounting-Request
From the client to the server. A packet of this type carries user
information for the server to start or stop accounting for the
user. The Acct-Status-Type attribute in the packet indicates
whether to start or stop accounting.
5 Accounting-Response
From the server to the client. The server sends a packet of this
type to notify the client that it has received the Accounting-
Request and has correctly recorded the accounting
information.
2.
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
identifier.
3.
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