Basic Operation
All communications regarding
RADIUS
accounting are done with an Accounting-Request
packet. A client that is participating in the RADIUS accounting
process will generate an Accounting Start
packet,
which is a specific kind of Accounting-Request
packet. This packet includes information on which service has been
provisioned and on the user for which these services are provided.
This packet is sent to the RADIUS accounting server, which will then
acknowledge receipt of the data. When the client is finished with the
network services, it will send to the accounting server an
Accounting Stop
packet (again, a specialized
Accounting-Request
packet), which will include the
service delivered; usage statistics such as time elapsed, amount
transferred, average speed; and other details. The accounting server
acknowledges receipt of the stop packet, and all is well. If the
server does not or cannot handle the contents of the
Accounting-Request
packet, it is not allowed to
send a receipt acknowledgment to the client.
In this instance, the RFC recommends that a client continue to send
its packets to the accounting server when it has not received an
acknowledgment that its Accounting-Request
packet
has been processed. In fact, in large distributed networks, it is
desirable to have several accounting servers act in a round-robin
fashion to handle failover and redundancy needs. An administrator can
carry this mentality further and designate certain accounting servers
to handle different requests—one for his dial-up users, one for
his DSL customers, and yet another for ISDN connections.
Additionally, the proxy functionality present in the authentication
and authorization realms of RADIUS are also allowed in the accounting
phase, as the accounting server may make requests of other servers to
assist in the processing of Accounting-Request
packets.
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