Cisco Cisco Packet Data Interworking Function (PDIF)
Interchassis Session Recovery
Overview ▀
ASR 5500 System Administration Guide, StarOS Release 17 ▄
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Important:
ICSR support for LAC requires a separate LAC license, as well as an Inter-Chassis Session Recovery
license.
Important:
Contact your Cisco account representative to verify whether a specific service supports ICSR as an
option.
Interchassis Communication
Chassis configured to support ICSR communicate using periodic Hello messages. These messages are sent by each
chassis to notify the peer of its current state. The Hello message contains information about the chassis such as its
configuration and priority. A dead interval is used to set a time limit for a Hello message to be received from the
chassis’ peer. If the standby chassis does not receive an Hello message from the active chassis within the dead interval,
the standby chassis transitions to the active state. In situations where the SRP link goes out of service, a priority scheme
is used to determine which chassis processes the session. The following priority scheme is used:
chassis to notify the peer of its current state. The Hello message contains information about the chassis such as its
configuration and priority. A dead interval is used to set a time limit for a Hello message to be received from the
chassis’ peer. If the standby chassis does not receive an Hello message from the active chassis within the dead interval,
the standby chassis transitions to the active state. In situations where the SRP link goes out of service, a priority scheme
is used to determine which chassis processes the session. The following priority scheme is used:
route modifier
chassis priority
MIO/UMIO MAC address
Checkpoint Messages
Checkpoint messages are sent from the active chassis to the standby chassis. These messages are sent at specific
intervals and contain all the information needed to recreate the sessions on the standby chassis, if that chassis were to
become active. Once a session exceeds the checkpoint duration, checkpoint data is collected on the session.
intervals and contain all the information needed to recreate the sessions on the standby chassis, if that chassis were to
become active. Once a session exceeds the checkpoint duration, checkpoint data is collected on the session.
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.
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:
A switchover event caused by an AAA monitoring failure is non-revertible.
If the newly active chassis fails to monitor the configured AAA servers, it remains as the active chassis until one of the
following occurs:
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