Cisco Asr 9000 Series Aggregation Services Router Broadband Network Gateway Configuration Guide - Cisco ASR 9000 Series Configuration Manual

Configuring Authentication, Authorization, and Accounting Functions
AAA Overview
2865). The RADIUS server manages the AAA process by interacting with BNG, and databases and directories
containing user information.
The RADIUS protocol runs on a distributed client-server system. The RADIUS client runs on BNG (Cisco
ASR 9000 Series Router) that sends authentication requests to a central RADIUS server. The RADIUS server
contains all user authentication and network service access information.
The AAA processes, the role of RADIUS server during these processes, and some BNG restrictions, are
explained in these sections:
Authentication
The authentication process identifies a subscriber on the network, before granting access to the network and
network services. The process of authentication works on a unique set of criteria that each subscriber has for
gaining access to the network. Typically, the RADIUS server performs authentication by matching the
credentials (user name and password) the subscriber enters with those present in the database for that subscriber.
If the credentials match, the subscriber is granted access to the network. Otherwise, the authentication process
fails, and network access is denied.
Authorization
After the authentication process, the subscriber is authorized for performing certain activity. Authorization is
the process that determines what type of activities, resources, or services a subscriber is permitted to use. For
example, after logging into the network, the subscriber may try to access a database, or a restricted website.
The authorization process determines whether the subscriber has the authority to access these network resources.
AAA authorization works by assembling a set of attributes based on the authentication credentials provided
by the subscriber. The RADIUS server compares these attributes, for a given username, with information
contained in a database. The result is returned to BNG to determine the actual capabilities and restrictions
that are to be applied for that subscriber.
Accounting
The accounting keeps track of resources used by the subscriber during network access. Accounting is used
for billing, trend analysis, tracking resource utilization, and capacity planning activities. During the accounting
process, a log is maintained for network usage statistics. The information monitored include, but are not
limited to - subscriber identities, applied configurations on the subscriber, the start and stop times of network
connections, and the number of packets and bytes transferred to, and from, the network.
BNG reports subscriber activity to the RADIUS server in the form of accounting records. Each accounting
record comprises of an accounting attribute value. This value is analyzed and used by the RADIUS server for
network management, client billing, auditing, etc.
The accounting records of the subscriber sessions may timeout if the BNG does not receive acknowledgments
from the RADIUS server. This timeout can be due to RADIUS server being unreachable or due to network
connectivity issues leading to slow performance of the RADIUS server. If the sessions on the BNG are not
acknowledged for their Account-Start request, loss of sessions on route processor fail over (RPFO) and other
critical failures are reported. It is therefore recommended that a RADIUS server deadtime be configured on
the BNG, to avoid loss of sessions. Once this value is configured, and if a particular session is not receiving
an accounting response even after retries, then that particular RADIUS server is considered to be non-working
and further requests are not sent to that server.
The radius-server deadtime limit command can be used to configure the deadtime for RADIUS server. For
details, see Configuring RADIUS Server Settings, on page 43.

Cisco ASR 9000 Series Aggregation Services Router Broadband Network Gateway Configuration Guide,

Release 4.3.x
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