3Com 4500G Family Configuration Manual page 562

Figure 1-4 RADIUS packet format
Descriptions of the fields are as follows:
2) The Code field (1-byte long) is for indicating the type of the RADIUS packet.
possible values and their meanings.
Table 1-1 Main values of the Code field
Code
1 Access-Request
2 Access-Accept
3 Access-Reject
4 Accounting-Request
5 Accounting-Response
3) The Identifier field (1-byte long) is for matching request packets and response packets and
detecting retransmitted request packets. The request and response packets of the same type have
the 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 to
4096. Bytes beyond the length are considered the padding and are neglected upon reception. If the
length of a received packet is less than that indicated by the Length field, the packet is dropped.
Packet type
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.
From the server to the client. If all the attribute values
carried in the Access-Request are acceptable, that is,
the authentication succeeds, the server sends an
Access-Accept response.
From the server to the client. If any attribute value
carried in the Access-Request is unacceptable, the
server rejects the user and sends an
Access-Reject response.
From the client to the server. A packet of this type
carries user information for the server to start/stop
accounting for the user. It contains the
Acct-Status-Type attribute, which indicates
whether the server is requested to start the
accounting or to end the accounting.
From the server to the client. The server sends to
the client a packet of this type to notify that it has
received the Accounting-Request and has
correctly started recording the accounting
information.
1-5
Table 1-1 gives the
Description