Aaa Monitor - Cisco ASR 5000 Series Administration Manual

Interchassis Session Recovery
For additional information about the output of show srp commands, see the Statistics and Counters Reference.

AAA Monitor

AAA servers are monitored using the authentication probe mechanism. AAA servers are considered Up if the
authentication-probe receives a valid response. AAA servers are considered Down when the max-retries
count specified in the configuration of the AAA server has been reached. SRP initiates a switchover when
none of the configured AAA servers responds to an authentication probe. AAA probing is only performed on
the active chassis.
Important
If the newly active chassis fails to monitor the configured AAA servers, it remains as the active chassis until
one of the following occurs:
• a manual switchover
• another non-AAA failure event causes the system to switchover
• a CLI command is used to clear the AAA failure flag and allow the chassis to switch to standby
BGP Interaction
The Service Redundancy Protocol implements revertible switchover behavior via a mechanism that adjusts
the route modifier value for the advertised loopback/IP Pool routes. The initial value of the route modifier
value is determined by the chassis' configured role and is initialized to a value that is higher than a normal
operational value. This ensures that in the event of an SRP link failure and an SRP task failure, the correct
chassis is still preferred in the routing domain.
Important
The Active and Standby chassis share current route modifier values. When BGP advertises the loopback and
IP pool routes, it converts the route modifier into an autonomous systems (AS) path prepend count. The Active
chassis always has a lower route modifier, and thus prepends less to the AS-path attribute. This causes the
route to be preferred in the routing domain.
If communication on the SRP link is lost, and both chassis in the redundant pair are claiming to be Active,
the previously Active chassis is still preferred since it is advertising a smaller AS-path into the BGP routing
domain. The route modifier is incremented as switchover events occur. A threshold determines when the route
modifier should be reset to its initial value to avoid rollover.
Requirements
ICSR configurations require the following:
A switchover event caused by an AAA monitoring failure is non-revertible.
For ICSR you must configure busyout ip pool commands in the same order on Active and Standby chassis
to avoid SRP validation failures.
ASR 5500 System Administration Guide, StarOS Release 21.4
AAA Monitor
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