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4. Packet Types

The RADIUS packet type is determined by the Code field in the first octet of the packet.

4.1. Accounting-Request​

Description​

Accounting-Request packets are sent from a client (typically a Network Access Server or its proxy) to a RADIUS accounting server, and convey information used to provide accounting for a service provided to a user. The client transmits a RADIUS packet with the Code field set to 4 (Accounting-Request).

Upon receipt of an Accounting-Request, the server MUST transmit an Accounting-Response reply if it successfully records the accounting packet, and MUST NOT transmit any reply if it fails to record the accounting packet.

Any attribute valid in a RADIUS Access-Request or Access-Accept packet is valid in a RADIUS Accounting-Request packet, except that the following attributes MUST NOT be present in an Accounting-Request: User-Password, CHAP-Password, Reply-Message, State. Either NAS-IP-Address or NAS-Identifier MUST be present in a RADIUS Accounting-Request. It SHOULD contain a NAS-Port or NAS-Port-Type attribute or both unless the service does not involve a port or the NAS does not distinguish among its ports.

If the Accounting-Request packet includes a Framed-IP-Address, that attribute MUST contain the IP address of the user. If the Access-Accept used the special values for Framed-IP-Address telling the NAS to assign or negotiate an IP address for the user, the Framed-IP-Address (if any) in the Accounting-Request MUST contain the actual IP address assigned or negotiated.

A summary of the Accounting-Request packet format is shown below.

The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |  Identifier   |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                     Request Authenticator                     |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+

Code​

4 for Accounting-Request.

Identifier​

The Identifier field MUST be changed whenever the content of the Attributes field changes, and whenever a valid reply has been received for a previous request. For retransmissions where the contents are identical, the Identifier MUST remain unchanged.

Note that if Acct-Delay-Time is included in the attributes of an Accounting-Request then the Acct-Delay-Time value will be updated when the packet is retransmitted, changing the content of the Attributes field and requiring a new Identifier and Request Authenticator.

Request Authenticator​

The Request Authenticator of an Accounting-Request contains a 16-octet MD5 hash value calculated according to the method described in "Request Authenticator" above.

Attributes​

The Attributes field is variable in length, and contains a list of Attributes.

4.2. Accounting-Response​

Description​

Accounting-Response packets are sent by the RADIUS accounting server to the client to acknowledge that the Accounting-Request has been received and recorded successfully. If the Accounting-Request was recorded successfully then the RADIUS accounting server MUST transmit a packet with the Code field set to 5 (Accounting-Response). On reception of an Accounting-Response by the client, the Identifier field is matched with a pending Accounting-Request. The Response Authenticator field MUST contain the correct response for the pending Accounting-Request. Invalid packets are silently discarded.

A RADIUS Accounting-Response is not required to have any attributes in it.

A summary of the Accounting-Response packet format is shown below. The fields are transmitted from left to right.

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Code      |  Identifier   |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                     Response Authenticator                    |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Attributes ...
+-+-+-+-+-+-+-+-+-+-+-+-+

Code​

5 for Accounting-Response.

Identifier​

The Identifier field is a copy of the Identifier field of the Accounting-Request which caused this Accounting-Response.

Response Authenticator​

The Response Authenticator of an Accounting-Response contains a 16-octet MD5 hash value calculated according to the method described in "Response Authenticator" above.

Attributes​

The Attributes field is variable in length, and contains a list of zero or more Attributes.

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