Cisco Cisco Packet Data Gateway (PDG)
Interchassis Session Recovery
ICSR Operation ▀
ASR 5500 System Administration Guide, StarOS Release 18 ▄
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Chassis Initialization
When the chassis are simultaneously initialized, they send Hello messages to their configured peer. The peer sends a
response, establishes communication between the chassis, and messages are sent that contain configuration information.
response, establishes communication between the chassis, and messages are sent that contain configuration information.
During initialization, if both chassis are misconfigured in the same mode - both active (primary) or both standby
(backup), the chassis with the highest priority (lowest number set with the ICSR priority command) becomes active and
the other chassis becomes the standby.
(backup), the chassis with the highest priority (lowest number set with the ICSR priority command) becomes active and
the other chassis becomes the standby.
If the chassis priorities are the same, the system compares the two MAC addresses and the chassis with the higher
MIO/UMIO MAC address becomes active. For example, if the chassis have MAC addresses of 00-02-43-03-1C-2B and
00-02-43-03-01-3B, the last 3 sets of octets (the first 3 sets are the vendor code) are compared. In this example, the 03-
1C-2B and 03-01-3B are compared from left to right. The first pair of octets in both MAC addresses are the same, so the
next pairs are compared. Since the 01 is lower than the 1C, the chassis with the MIO/UMIO MAC address of 00-02-43-
03-1C-2B becomes active and the other chassis the standby.
MIO/UMIO MAC address becomes active. For example, if the chassis have MAC addresses of 00-02-43-03-1C-2B and
00-02-43-03-01-3B, the last 3 sets of octets (the first 3 sets are the vendor code) are compared. In this example, the 03-
1C-2B and 03-01-3B are compared from left to right. The first pair of octets in both MAC addresses are the same, so the
next pairs are compared. Since the 01 is lower than the 1C, the chassis with the MIO/UMIO MAC address of 00-02-43-
03-1C-2B becomes active and the other chassis the standby.
Chassis Operation
This section describes how the chassis communicate, maintain subscriber sessions, and perform chassis switchover.
Chassis Communication
If one chassis in the active state and one in the standby state, they both send Hello messages at each hello interval.
Subscriber sessions that exceed the checkpoint session duration are included in checkpoint messages that are sent to the
standby chassis. The checkpoint message contains subscriber session information so if the active chassis goes out of
service, the backup chassis becomes active and is able to continue processing the subscriber sessions. Additional
checkpoint messages occur at various intervals whenever subscriber session information is updated on the standby
chassis.
Subscriber sessions that exceed the checkpoint session duration are included in checkpoint messages that are sent to the
standby chassis. The checkpoint message contains subscriber session information so if the active chassis goes out of
service, the backup chassis becomes active and is able to continue processing the subscriber sessions. Additional
checkpoint messages occur at various intervals whenever subscriber session information is updated on the standby
chassis.
For additional information see the Service Redundancy Protocol Configuration Mode Commands chapter in the
Command Line Interface Reference.
Command Line Interface Reference.
Chassis Switchover
If the active chassis goes out of service, the standby chassis continues to send Hello messages. If the standby chassis
does not receive a response to the Hello messages within the dead interval, the standby chassis initiates a switchover.
During the switchover, the standby chassis begins advertising its srp-activated loopback and pool routes into the routing
domain. Once the chassis becomes active, it continues to process existing AAA services and subscriber sessions that had
checkpoint information, and is also able to establish new subscriber sessions.
does not receive a response to the Hello messages within the dead interval, the standby chassis initiates a switchover.
During the switchover, the standby chassis begins advertising its srp-activated loopback and pool routes into the routing
domain. Once the chassis becomes active, it continues to process existing AAA services and subscriber sessions that had
checkpoint information, and is also able to establish new subscriber sessions.
When the primary chassis is back in service, it sends Hello messages to the configured peer. The peer sends a response,
establishes communication between the chassis, and sends Hello messages that contain configuration information. The
primary chassis receives an Hello message that shows the backup chassis state as active and then transitions to standby.
The Hello messages continue to be sent to each peer, and checkpoint information is now sent from the active chassis to
the standby chassis at regular intervals.
establishes communication between the chassis, and sends Hello messages that contain configuration information. The
primary chassis receives an Hello message that shows the backup chassis state as active and then transitions to standby.
The Hello messages continue to be sent to each peer, and checkpoint information is now sent from the active chassis to
the standby chassis at regular intervals.
When chassis switchover occurs, the session timers are recovered. The access gateway session recovery is recreated
with the full lifetime to avoid potential loss of the session and the possibility that a renewal update was lost in the
transitional checkpoint update process.
with the full lifetime to avoid potential loss of the session and the possibility that a renewal update was lost in the
transitional checkpoint update process.