This configuration assigns a chassis mode and priority, and also configures the redundancy link between the primary and backup chassis:

configure 
  context srp_ctxt_name 
    service-redundancy-protocol 
      chassis-mode { primary | backup } 
      priority priority 
      peer-ip-address ip_address 
      hello-interval dur_sec 
      dead-interval dead_dur_sec 
      end 

Notes:

Guard timers ensure that local failures, such as reboots and task restarts, do not result in ICSR events which can be disruptive.

The guard timer command configures the redundancy-guard-period and monitor-damping-period for SRP service monitoring.

configure 
  context context_name 
    service-redundancy-protocol variable 
      guard-timer { aaa-switchover-timers { damping-period seconds | guard-period seconds } | diameter-switchover-timers { damping-period seconds | guard-period seconds } | srp-redundancy-timers { aaa  { damping-period seconds | guard-period seconds } | bgp { damping-period seconds | guard-period seconds } | diam  { damping-period seconds | guard-period seconds } } 
      end 

Notes:

• aaa-switchover-timers – sets timers that prevent back-to-back ICSR switchovers due to an AAA failure (post ICSR switchover) while the network is still converging.

  • damping-period – configures a delay time to trigger an ICSR switchover due to a monitoring failure within the guard-period.

  • guard-period – configures the local-failure-recovery network-convergence timer.

• diameter-switchover-timers – sets timers that prevent a back-to-back ICSR switchover due to a Diameter failure (post ICSR switchover) while the network is still converging.

  • damping-period – configures a delay time to trigger an ICSR switchover due to a monitoring failure within the guard-period.

  • guard-period – configures the local-failure-recovery network-convergence timer.

• srp-redundancy-timers – sets timers that prevent an ICSR switchover while the system is recovering from a local card-reboot/critical-task-restart failure.

  • aaa – local failure followed by AAA monitoring failure

  • bgp – local failure followed by BGP monitoring failure

  • diam – local failure followed by Diameter monitoring failure

You can enable separate DSCP marking of SRP control and checkpoint messages. The dscp-marking command sets DSCP marking values for SRP control and checkpoint (session maintenance) messages.

configure 
  context context_name 
    service-redundancy-protocol 
      dscp-marking { control | session } dscp_value 

Notes:

The ICSR framework reduces switchover disruption for VoLTE traffic by enabling VoLTE traffic on the newly active gateway prior to reconciling the billing information and enabling communication with the newly active gateway when accounting is not deemed critical.

The switchover allow-all-data-traffic SRP Configuration mode CLI command allows all data traffic (VoLTE and non-VoLTE) during switchover transition. This command overwrites the switchover allow-volte-data-traffic command if enabled on a P-GW.

configure 
  context context_name 
    service-redundancy-protocol 
      switchover allow-all-data-traffic 

Important

The switchover allow-all-data-traffic command must be run on both chassis to enable this feature.

The switchover allow-volte-data-traffic SRP Configuration mode CLI command allows VoLTE data traffic during ICSR switchover transition.

configure 
  context context_name 
    service-redundancy-protocol 
      switchover allow-volte-data-traffic [ maintain-accounting ] 

Notes:

The SRP Configuration mode switchover allow-all-data-traffic command allows all data traffic (VoLTE and non-VoLTE) during switchover transition. This command overwrites the switchover allow-volte-data-traffic command if enabled on a P-GW. This feature reduces data traffic outage during the switchover.

Important

This CLI command must be run on both the active and standby chassis to enable this feature.

All data traffic is allowed on the active chassis during flushing and internal auditing. The billing information is reconciled in the background once the flush is complete.

The SRP Configuration mode switchover allow-early-active-transition command enables early transition to active state during an ICSR switchover. By default this feature is disabled.

Use this command in concert with the switchover allow-all-data-traffic or allow-volte-data-traffic (without maintain accounting option) command to further reduce data outage during a planned switchover. The outage window is the amount time between initiating an ICSR switchover and when the newly active chassis starts processing data.

Important

You must enable one of the commands identified above on both ICSR chassis prior to enabling this command.

During an Audit on the gateways (P-GW/S-GW/GGSN/SAE-GW) after Session Recovery or an ICSR event, if any critical information, internally or externally related to a subscriber session seems inconsistent, ICSR will locally purge the associated session information.

Since external gateways (peer nodes) are unaware of the purging of this session, the UE session may be maintained at other nodes. This leads to hogging of resources external to the gateway and an unreachable UE for VoLTE calls.

When this feature is enabled, graceful cleanup for an ICSR audit of failed calls occurs. External signaling notifies peers of session termination before purging the session. The gateway will attempt to notify external peers of the removal of the session. External nodes to the local gateway include S-GW, P-GW, SGSN, MME, AAA, PCRF and IMSA.

Audit failure can occur because of missing or incomplete session information. Therefore, only the peers for which the information is available will be notified.

configure 
  require graceful-cleanup-during-audit-failure [ del-cause non-ims-apn   { system-failure | none } ] 

The ICSR framework minimizes control outage time associated with the flushing of critical full checkpoint statistics, network convergence and internal auditing.

The amount of time consumed by the following activities affects control outage time during switchover:

The switchover control-outage-optimization CLI command allows new calls during the Accounting Flush, as soon as the Audit is completed. This SRP Configuration mode command enables the quicker restoration of control traffic (call-setup, modification, deletion) following an ICSR switchover.

configure 
  context context_name 
    service-redundancy-protocol 
      switchover control-outage-optimization 
      end 

Transport (TCP) level re-transmission is supported on the SRP link between ICSR chassis. SRP configuration also supports optional application level checks to ensure checkpoints are received at the Standby chassis. Failed attempts to receive and apply checkpoints send NACK messages to the Active chassis.

When this feature is enabled and the standby chassis sends a NACK in response to the receipt of a micro-checkpoint (MC) that fails to be successfully applied, the standby chassis sends another NACK. The standby chassis will send more NACKs (configurable, default = 3) within a 10-minute window if a macro-checkpoint (FC) is not received. NACKs will continue to be sent and the 10-minute reset until an FC is received and applied, or the configured number of max-responses is reached.

You can also specify the number of times a NACK is sent within the 10-minute window in response to a failed MC or FC (Default = 3).

A nack keyword in the SRP Configuration mode checkpoint session command allows you to enable generation of NACK messages in response to checkpoint message failures on a Standby ICSR chassis.

Important

The nack keyword will only appear if a special ICSR optimization feature license has been purchased and installed. Contact your Cisco account representative for assistance.

configure 
   context context_name 
      service-redundancy-protocol variable 
         checkpoint session nack { macro | micro } [ max-response number ]  
         no checkpoint session nack { macro | micro }  
         end 

Notes:

A periodic-interval keyword in the SRP Configuration mode checkpoint session command allows you to configure the interval between the sending of macro-checkpoints (FCs) between the active and standby chassis.

Important

The periodic-interval keyword will only appear if a special ICSR optimization feature license has been purchased and installed. Contact your Cisco account representative for assistance.

configure 
   context context_name 
      service-redundancy-protocol variable 
         checkpoint session periodic-interval minutes  
         default checkpoint session periodic-interval  
         no checkpoint session periodic-interval  
         end 

The NACK mechanism sends a NACK message for any ICSR checkpoint failure on the standby chassis. Every NACK sent from the standby chassis triggers a full checkpoint from the active chassis.

If the micro-checkpoint is failing continuously and sending NACKs, the active chassis keeps sending full-checkpoints. This increases SRP bandwidth.

CLI commands allow an operator to selectively disable and re-enable NACK messages for specific micro-checkpoints.

The Exec mode srp disable nack micro-chkpt-cmd disables the sending of a NACK from the standby chassis.

srp disable nack micro-chkpt-cmd  chkpt_number 

chkpt_number specifies the checkpoint number to be disabled as an integer from 1 through 255. You can obtain checkpoint numbers (CMD IDs) from the output of the show srp checkpoint info command.

You can re-enable the micro-checkpoint using the srp enable nack micro-chkpt-cmd command.

srp enable nack micro-chkpt-cmd  chkpt_number