> Session Recovery
> With robust hardware failover and redundancy protection, any card-level hardware failures on the system can quickly be corrected. However, software failures can occur for numerous reasons, often without prior indication.
> This appendix describes the Session Recovery feature that provides seamless failover and reconstruction of subscriber session information in the event of a hardware or software fault.
> This appendix includes the following sections:

> • | How Session Recovery Works

> • | Additional Hardware Requirements

> • | Configuring the System to Support Session Recovery

> How Session Recovery Works
> This section provides an overview of how this feature is implemented and the recovery process.
> The Session Recovery feature provides seamless failover and reconstruction of subscriber session information in the event of a hardware or software fault within the system preventing a fully connected user session from being disconnected.
> Session recovery is performed by mirroring key software processes (for example, session manager and AAA manager) within the system. These mirrored processes remain in an idle state (standby-mode) wherein they perform no processing, until they may be needed in the event of a software failure (for example, a session manager task aborts).
> The system spawns new instances of “standby mode” session and AAA managers for each active control processor (CP) being used. These mirrored processes require both memory and processing resources, which means that additional hardware may be required to enable this feature (see the Additional Hardware Requirements section).
> Other key system-level software tasks, such as VPN manager, are performed on a physically separate packet processing card to ensure that a double software fault (for example, session manager and VPN manager fails at same time on same card) cannot occur. The packet processing card that hosts the VPN manager process is in active mode and reserved by the operating system for this sole use when session recovery is enabled.
> There are two modes of session recovery.

> • | Task recovery mode: Wherein one or more session manager failures occur and are recovered without the need to use resources on a standby packet processing card. In this mode, recovery is performed by using the mirrored “standby-mode” session manager task(s) running on active packet processing cards. The “standby-mode” task is renamed, made active, and is then populated using information from other tasks such as AAA manager. In case of Task failure, limited subscribers will be affected and will suffer outage only until the task starts back up.

> • | Full packet processing card recovery mode: Used when a packet processing card hardware failure occurs, or when a planned packet processing card migration fails. In this mode, the standby packet processing card is made active and the “standby-mode” session manager and AAA manager tasks on the newly activated packet processing card perform session recovery.

> Session/Call state information is saved in the peer AAA manager task because each AAA manager and session manager task is paired together. These pairs are started on physically different packet processing cards to ensure task recovery.
> There are some situations wherein session recovery may not operate properly. These include:

> • | Additional software or hardware failures occur during the session recovery operation. For example, an AAA manager fails while the state information it contained was being used to populate the newly activated session manager task.

> • | A lack of hardware resources (packet processing card memory and control processors) to support session recovery.

> Important: After a session recovery operation, some statistics, such as those collected and maintained on a per manager basis (AAA Manager, Session Manager, etc.) are in general not recovered, only accounting and billing related information is checkpointed and recovered.
> Session Recovery is available for the following functions:

> • | Any session needing L2TP LAC support (excluding regenerated PPP on top of an HA/GGSN session)

> • | Closed RP PDSN services supporting simple IP, Mobile IP, and Proxy Mobile IP

> • | CSCF sessions

> • | GGSN services for IPv4 and PPP PDP contexts

> • | HA services supporting Mobile IP and/or Proxy Mobile IP session types with or without per-user Layer 3 tunnels

> • | HNB-GW: HNB Session over IuH

> • | HNB-GW: HNB-CN Session over IuPS and IuCS

> • | HNB-GW: SeGW Session IPSec Tunnel

> • | HSGW services for IPv4

> • | IPSG-only systems

> • | LNS session types

> • | PDSN services supporting simple IP, Mobile IP, and Proxy Mobile IP

> • | P-GW services for IPv4

> • | SGSN services (3G and 2.5G services) for IPv4 and PPP PDP contexts

> Session recovery is not supported for the following functions:

> • | Any session using IPv6 (PDSN/GGSN/SGSN/LNS)

> • | Any session needing L2TP LAC support (including regenerated PPP on top of an HA/GGSN session)

> • | Destination-based accounting recovery

> • | GGSN network initiated connections

> • | GGSN session using more than 1 service instance

> • | MIP/L2TP with IPSec integration

> • | MIP session with multiple concurrent bindings

> • | Mobile IP sessions with L2TP

> • | Multiple MIP sessions

> Important: Session Recovery is a licensed Cisco feature. A separate feature license may be required. Contact your Cisco account representative for detailed information on specific licensing requirements. For information on installing and verifying licenses, refer to the Managing License Keys section of the Software Management Operations chapter in the System Administration Guide.
> When session recovery occurs, the system reconstructs the following subscriber information:

> • | Data and control state information required to maintain correct call behavior.

> • | A minimal set of subscriber data statistics; required to ensure that accounting information is maintained.

> • | A best-effort attempt to recover various timer values such as call duration, absolute time, and others.

> • | The idle time timer is reset to zero and the re-registration timer is reset to its maximum value for HA sessions to provide a more conservative approach to session recovery.

> Important: Any partially connected calls (for example, a session where HA authentication was pending but has not yet been acknowledged by the AAA server) are not recovered when a failure occurs.
> Additional Hardware Requirements
> Because session recovery requires numerous hardware resources, such as memory, control processors, NPU processing capacity, etc., some additional hardware may be required to ensure that enough resources are available to fully support this feature.
> Important: A minimum of four packet processing cards (three active and one standby) per individual chassis is required to use this feature.
> To allow for complete session recovery in the event of a hardware failure during a packet processing card migration, a minimum of three active packet processing cards and two standby packet processing cards should be deployed.
> To assist you in your network design and capacity planning, consider the following factors:

> • | Subscriber capacity is decreased depending on the hardware configuration. A fully configured chassis would experience a smaller decrease in subscriber capacity versus a minimally configured chassis.

> • | The amount by which control transaction processing capacity is reduced.

> • | The reduction in subscriber data throughput.

> • | The recovery time for a failed software task.

> • | The recovery time for a failed packet processing card.

> A packet processing card migration may temporarily impact session recovery as hardware resources (memory, processors, etc.) that may be needed are not available during the migration. To avoid this condition, a minimum of two standby packet processing cards should be configured.
> Configuring the System to Support Session Recovery
> The following procedures allow you to configure the session recovery feature for either an operational system that is currently in-service (able to accept incoming calls) or a system that is out-of-service (not part of your production network and, therefore, not processing any live subscriber/customer data).
> Important: The session recovery feature, even when the feature use key is present, is disabled by default on the system.
> Enabling Session Recovery
> As noted earlier, session recovery can be enabled on a system that is out-of-service (OOS) and does not yet have any contexts configured, or on an in-service system that is currently capable of processing calls. However, if the system is in-service, it must be restarted before the session recovery feature takes effect.
> Enabling Session Recovery on an Out-of-Service System
> The following procedure is for a system that does not have any contexts configured.
> To enable the session recovery feature on an out-of-service system, follow the procedure below. This procedure assumes that you begin at the Exec mode prompt.

> Step 1 | At the Exec mode prompt, verify that the session recovery feature is enabled by the session and feature use license on the system by running the show license info command:

> The output of this command appears similar to the example shown below. Note that the session recovery feature is bold-faced in this example.
> Key Information (installed key):
> Comment <Host Name>
> CF Device 1 Model: "SanDiskSDCFB-512"
> Serial Number: "115212D1904T0314"
> CF Device 2 Model: "SanDiskSDCFB-512"
> Serial Number: "115206D1904S5951"
> Date of Issue Thursday May 12 14:35:50 EDT 2005
> Issued By <Vendor Name>
> Key Number 17120
> Enabled Features:
> Part Number Quantity Feature
> ----------- -------- -----------------------
> xxx-xx-xxxx 15 PDSN/GGSN/SGSN (10K)
> [none] - FA
> [none] - IPv4 Routing Protocols
> xxx-xx-xxxx - IPSec
> xxx-xx-xxxx - 2TP LAC (PDSN/GGSN/SGSN)
> xxx-xx-xxxx 1 L2TP LNS (10K)
> xxx-xx-xxxx 6 L2TP LNS (1K)
> xxx-xx-xxxx - Session Recovery (PDIF/PDSN/GGSN/SGSN)
> [none] - Session Recovery (HA)
> xxx-xx-xxxx - PCF Monitoring
> xxx-xx-xxxx - Layer 2 Traffic Management
> Session Limits:
> Sessions Session Type
> -------- -----------------------
> 150000 PDSN/GGSN/SGSN
> Status:
> 16000 L2TP LNS
> CF Device 1 Does not match either SPC
> CF Device 2 Does not match either SPC
> License Status Good (Not Redundant)
> Important: If the current status of the Session Recovery feature is Disabled, you cannot enable this feature until a license key is installed in the system.

> Step 2 | Use the following configuration example to enable session recovery.

> configure
> require session recovery
> end

> Step 3 | Save your configuration as described in the Verifying and Saving Your Configuration chapter of this guide.

> The system, when started, enables session recovery, creates all mirrored “standby-mode” tasks, and performs packet processing card reservations and other operations automatically.

> Step 4 | After the system has been configured and placed in-service, you should verify the preparedness of the system to support this feature as described in the Viewing Session Recovery Status section.

> Enabling Session Recovery on an In-Service System
> When enabling session recovery on a system that already has a saved configuration, the session recovery commands are automatically placed before any service configuration commands in the configuration file.
> To enable the session recovery feature on an in-service system, follow the procedure below. This procedure assumes that you begin at the Exec mode prompt.

> Step 1 | At the Exec mode prompt, verify that the session recovery feature is enabled by the session and feature use license on the system by running the show license info command:

> The output of this command appears similar to the example shown below. Note that the session recovery feature is bold-faced in this example.
> Key Information (installed key):
> Comment <Host Name>
> CF Device 1 Model: "SanDiskSDCFB-512"
> Serial Number: "115212D1904T0314"
> CF Device 2 Model: "SanDiskSDCFB-512"
> Serial Number: "115206D1904S5951"
> Date of Issue Thursday May 12 14:35:50 EDT 2005
> Issued By <Vendor Name>
> Key Number 17120
> Enabled Features:
> Part Number Quantity Feature
> ----------- -------- -----------------------
> xxx-xx-xxxx 15 PDSN/GGSN/SGSN (10K)
> [none] - FA
> [none] - IPv4 Routing Protocols
> xxx-xx-xxxx - IPSec
> xxx-xx-xxxx - 2TP LAC (PDSN/GGSN/SGSN)
> xxx-xx-xxxx 1 L2TP LNS (10K)
> xxx-xx-xxxx 6 L2TP LNS (1K)
> xxx-xx-xxxx - Session Recovery (PDIF/PDSN/GGSN/SGSN)
> [none] - Session Recovery (HA)
> xxx-xx-xxxx - PCF Monitoring
> xxx-xx-xxxx - Layer 2 Traffic Management
> Session Limits:
> Sessions Session Type
> -------- -----------------------
> 150000 PDSN/GGSN/SGSN
> Status:
> 16000 L2TP LNS
> CF Device 1 Does not match either SPC
> CF Device 2 Does not match either SPC
> License Status Good (Not Redundant)
> Important: If the current status of the Session Recovery feature is Disabled, you cannot enable this feature until a license key is installed in the system.

> Step 2 | Use the following configuration example to enable session recovery.

> configure
> require session recovery
> end
> Important: This feature does not take effect until after the system has been restarted.

> Step 3 | Save your configuration as described in the Verifying and Saving Your Configuration. chapter of this guide.

> Step 4 | Perform a system restart by entering the reload command:

> The following prompt appears:
> Are you sure? [Yes|No]:
> Confirm your desire to perform a system restart by entering yes.
> The system, when restarted, enables session recovery and creates all mirrored “standby-mode” tasks, performs packet processing card reservations, and other operations automatically.

> Step 5 | After the system has been restarted, you should verify the preparedness of the system to support this feature as described in the Viewing Session Recovery Status section.

> Important: More advanced users may opt to simply insert the require session recovery command syntax into an existing configuration file using a text editor or other means, and then applying the configuration file manually. Exercise caution when doing this to ensure that this command is placed among the first few lines of any existing configuration file; it must appear before the creation of any non-local context.
> Disabling the Session Recovery Feature
> To disable the session recovery feature on a system, enter the no require session recovery command from the Global Configuration mode prompt.
> Important: If this command is issued on an in-service system, then the system must be restarted by issuing the reload command.
> Viewing Session Recovery Status
> To determine if the system is capable of performing session recovery, when enabled, enter the show session recovery status verbose command from the Exec mode prompt.
> The output of this command should be similar to the examples shown below.
> [local]host_name# show session recovery status
> Session Recovery Status:
> Overall Status : SESSMGR Not Ready For Recovery
> Last Status Update : 1 second ago
> [local]host_name# show session recovery status
> Session Recovery Status:
> Overall Status : Ready For Recovery
> Last Status Update : 8 seconds ago
> [local]host_name# show session recovery status verbose
> Session Recovery Status:
> Overall Status : Ready For Recovery
> Last Status Update : 2 seconds ago
> ----sessmgr--- ----aaamgr---- demux
> cpu state active standby active standby active status
> ---- ------- ------ ------- ------ ------- ------ ------------
> 1/1 Active 2 1 1 1 0 Good
> 1/2 Active 1 1 0 0 0 Good
> 1/3 Active 1 1 3 1 0 Good
> 2/1 Active 1 1 1 1 0 Good
> 2/2 Active 1 1 0 0 0 Good
> 2/3 Active 2 1 3 1 0 Good
> 3/0 Active 0 0 0 0 1 Good (Demux)
> 3/2 Active 0 0 0 0 1 Good (Demux)
> 4/1 Standby 0 2 0 1 0 Good
> 4/2 Standby 0 1 0 0 0 Good
> 4/3 Standby 0 2 0 3 0 Good
> [local]host_name#
> Viewing Recovered Session Information
> To view session state information and any session recovery status, enter the following command:
> show subscriber debug-info { callid id | msid id | username name }

> Keyword/Variable | Description
> callid id | Displays subscriber information for the call specified by id. The call ID is an 8-byte hexadecimal number.
> msid id | Displays information for the mobile user identified by an MSID from 7 to 16 digits specified as an IMSI, MIN, or RMI. Wildcard characters $ and * are allowed. The * wildcard matches multiple characters and the $ wildcard matches a single character. If you do not want the wildcard characters interpreted as a wildcard enclose them in single quotes ( ‘ ). For example; ‘$’.
> username name | Displays information for connections for the subscriber identified by a previously configured username. name is a sequence of alpahnumeric characters and/or wildcard characters ('$' and '*') from 1 to 127 characters in length. The * wildcard matches multiple characters and the $ wildcard matches a single character. If you do not want the wildcard characters interpreted as wildcard enclose them in single quotes ( ‘). For example; ‘$’.

> ‌
> The following example shows the output of this command both before and after a session recovery operation has been performed. The “Redundancy Status” fields in this example have been bold-faced for clarity.
> username: user1 callid: 01ca11b1 msid: 0000100003
> Card/Cpu: 4/2
> Sessmgr Instance: 7
> Primary callline:
> Redundancy Status: Original Session
> Checkpoints Attempts Success Last-Attempt Last-Success
> Full: 69 68 29800ms 29800ms
> Micro: 206 206 20100ms 20100ms
> Current state: SMGR_STATE_CONNECTED
> FSM Event trace:
> State Event
> SMGR_STATE_OPEN SMGR_EVT_NEWCALL
> SMGR_STATE_NEWCALL_ARRIVED SMGR_EVT_ANSWER_CALL
> SMGR_STATE_NEWCALL_ANSWERED SMGR_EVT_LINE_CONNECTED
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_LINK_CONTROL_UP
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_IPADDR_ALLOC_SUCCESS
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_UPDATE_SESS_CONFIG
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_LOWER_LAYER_UP
> Data Reorder statistics
> Total timer expiry: 0 Total flush (tmr expiry): 0
> Total no buffers: 0 Total flush (no buffers): 0
> Total flush (queue full): 0 Total flush (out of range): 0
> Total flush (svc change): 0 Total out-of-seq pkt drop: 0
> Total out-of-seq arrived: 0
> IPv4 Reassembly Statistics:
> Success: 0 In Progress: 0
> Failure (timeout): 0 Failure (no buffers): 0
> Failure (other reasons): 0
> Redirected Session Entries:
> Allowed: 2000 Current: 0
> Added: 0 Deleted: 0
> Revoked for use by different subscriber: 0
> Peer callline:
> Redundancy Status: Original Session
> Checkpoints Attempts Success Last-Attempt Last-Success
> Full: 0 0 0ms 0ms
> Micro: 0 0 0ms 0ms
> Current state: SMGR_STATE_CONNECTED
> FSM Event trace:
> State Event
> SMGR_STATE_LINE_CONNECTED SMGR_EVT_LOWER_LAYER_UP
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_CONNECTED SMGR_EVT_REQ_SUB_SESSION
> SMGR_STATE_CONNECTED SMGR_EVT_RSP_SUB_SESSION
> SMGR_STATE_CONNECTED SMGR_EVT_ADD_SUB_SESSION
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_REQ
> SMGR_STATE_CONNECTED SMGR_EVT_AUTH_SUCCESS
> Data Reorder statistics
> Total timer expiry: 0 Total flush (tmr expiry): 0
> Total no buffers: 0 Total flush (no buffers): 0
> Total flush (queue full): 0 Total flush (out of range):0
> Total flush (svc change): 0 Total out-of-seq pkt drop: 0
> Total out-of-seq arrived: 0
> IPv4 Reassembly Statistics:
> Success: 0 In Progress: 0
> Failure (timeout): 0 Failure (no buffers): 0
> Failure (other reasons): 0
> Redirected Session Entries:
> Allowed: 2000 Current: 0
> Added: 0 Deleted: 0
> Revoked for use by different subscriber: 0
> Notice that is the example above, where the session has been recovered/recreated, that state events (FSM Event State field) no longer exist. This field is re-populated as new state changes occur.

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