Hopefully this helps you.
What Is Session and Service Accounting on the ASR9000?
The accounting features within the IOS-XR BNG software suite enable the functionality to keep track of the beginning and end of a session or service, along with the amount of bandwidth consumed on a per-subscriber or per-service basis. This is commonly used in prepaid service deployments when coupled with a PCRF (Policy and Charging Rules Function) server such as Cisco Prime with the BNG Service Manager or a third party solution.
How Does Service and Session Accounting Work?
When the BNG accounting features are enabled and a subscriber comes online, the ASR9K will generate an Account-Start message and send it to the configured RADIUS server. Next, at the defined session or service interval, period updates will be sent with amount of bytes in & out, packets in & out, as well as timing information. Lastly, when the session disconnects, an Account-Stop message will be sent from the ASR9K to the RADIUS service.
Note: This follows and is outlined in greater detail in RFC2866
What Is the Difference Between Session and Service Accounting?
Session accounting will provide the aforementioned information for the entire BNG session from when it first is established until it is disconnected. Service-Accounting however can be configured to send you stats for only a portion or a specific ‘service’ of the user’s BNG session.
For example, perhaps the configuration allows access to a few internet websites, but for a fee 100Mbytes of unrestricted internet access. A service dynamic-template can be configured (As compared to the common ipsubscriber or ppp template types) to remove an HTTP-Redirect policy and then begin Service Accounting, providing stats only while the ‘Unrestricted Internet’ service is active.
How Do I Configure Session Accounting?
Using a Dynamic-Template
In the main dynamic-template, session accounting can be activated using the configuration below. We would first create an aaa accounting subscriber method list name, in this case we chose ‘bng_accounting’. The type would be session and lastly the periodic-interval which determines how often we send the accounting-updates, which in this case is 1 minute.
aaa accounting subscriber bng_accounting group radius
dynamic-template
type <ipsubscriber|ppp> MAIN-DYN-TEMP
accounting aaa list bng_accounting type session periodic-interval 1 dual-stack-delay 5
Using RADIUS AV-Pairs
The following AV-pairs can be added to the BNG user’s RADIUS profile, which upon an Access-Accept message generated from RADIUS (Successful authentication) would trigger session accounting updates every minute. The interval and accounting-list AV-pairs are required; however the dual-stack-delay is optional.
cisco-avpair = subscriber:accounting-list=bng_accounting
cisco-avpair = acct-interval=1
cisco-avpair = subscriber:dual-stack-delay=<sec>
Note: The optional ‘dual-stack-delay’ feature delays the accounting updates from starting, which is meant to give enough time for the IPv4 and IPv6 addressing to complete as opposed to accounting updates triggering as soon as an IPv4 or IPv6 address is assigned. Mixing parts of the configuration from the dynamic-template with the av-pair for session accounting is not supported.
Note: RADIUS has preference over the dynamic template, do NOT configure both
How Do I Configure Service Accounting?
Using a Dynamic-Template
In a service dynamic-template, session accounting can be activated using the configuration below. We would first create an aaa accounting service method list name, in this case we chose ‘bng_accounting’. The type would be service and lastly the periodic-interval which determines how often we send the accounting-updates, which in this case is 1 minute.
aaa accounting service bng_accounting group radius
dynamic-template
type service SERVICE-DYN-TEMP
accounting aaa list bng_accounting type service periodic-interval 1
How Do I See the Accounting-Updates?
The ‘debug radius’ is a very verbose and clear way to see how often and what data is actually being sent within the RADIUS accounting messages. Here is an example of one:
Note: Unfortunately at this time, there is no filtering functionality for this debug, so this many not be feasible depending on how large of an environment exists.
How Can I Decipher the BNG Accounting Debug Messages?
When you have the 'debug radius' enabled to view or troubleshoot the BNG Accounting messages, generated by the ASR9K here are some of the key fields to look for:
Acct-Status-Type [40] 6 Start[0] <-- Generated upon session activation
Stop[0] <-- Generated upon session-disconnect
Watchdog[0] <-- Updates generated at interim interval
Acct-Input-Packets [47] 6 65 <-- Number of packets Rx by ASR9K since session/service activation.
Acct-Input-Octets [42] 6 4259 <-- Number of bytes Rx by ASR9K since session/service activation.
Acct-Output-Octets [43] 6 3355 <-- Number of packets Tx by ASR9K since session/service activation.
Acct-Output-Packets [48] 6 58 <-- Number of btyes Tx by ASR9K since session/service activation.
Cisco AVpair [1] 20 pppoe-session-id=7
General RADIUS Accounting Troubleshooting
Show subscribers session filter….detail internal
Show radius accounting
Debug aaa-subscriber all
Debug subscriber manager session next-subscriber
Sam
