Exclusive Configuration Change Access and Access Session Locking

Exclusive Configuration Change Access (also called the “Configuration Lock” feature) allows you to have exclusive change access to the Cisco IOS XE running configuration, preventing multiple users from making concurrent configuration changes.

The Access Session Locking addition to this feature extends the Exclusive Configuration Change Access feature such that show and debug commands entered by the user holding the configuration lock always have execution priority; show and debug commands entered by other users are only allowed to run after the processes initiated by the configuration lock owner have finished.

The Exclusive Configuration Change Access feature (“exposed lock”) is complementary with the locking mechanism in the Configuration Replace and Configuration Rollback feature (“rollback lock”).

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

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Information About Locking the Configuration

Exclusive Configuration Change Access and Access Session Locking

Devices running Cisco IOS software maintain a running configuration that determines the configuration state of the device. Changes to the running configuration alter the behavior of the device. Because Cisco IOS software allows multiple users to change the running configuration via the device CLI (including the device console and telnet Secure Shell (SSH)), in some operating environments it would be beneficial to prevent multiple users from making concurrent changes to the Cisco IOS running configuration. Temporarily limiting access to the Cisco IOS running configuration prevents inadvertent conflicts or cases where two users attempt to configure the same portion of the running configuration.

The Exclusive Configuration Change Access feature (also called the “Configuration Lock” feature) allows you to have exclusive change access to the Cisco IOS running configuration, preventing multiple users from making concurrent configuration changes.

This feature provides exclusive change access to the Cisco IOS running configuration from the time you enter global configuration mode by using the configure terminal command. This gives the effect of a “configuration lock,” preventing other users from changing the Cisco IOS running configuration. The configuration lock is automatically released when the user exits Cisco IOS configuration mode.

The Exclusive Configuration Change Access feature is enabled using the configuration mode exclusive command in global configuration mode. Exclusive configuration change access can be set to auto, so that the Cisco IOS configuration mode is locked whenever anyone uses the configure terminal command, or it can be set to manual, so that the Cisco IOS configuration mode is locked only when the configure terminal lock command is issued.

The Exclusive Configuration Change Access feature is complementary with the locking mechanism for the Configuration Replace and Configuration Rollback feature introduced in Cisco IOS Release 12.2(25)S and 12.3(7)T.

Access Session Locking

The Access Session Locking feature extends the Exclusive Configuration Change Access feature such that show and debug commands entered by the user holding the configuration lock always have execution priority. This feature prevents concurrent configuration access and also provides an option to prevent simultaneous processes, such as a show command entered by another user, from executing while other configuration commands are being executed. When this feature is enabled, the commands entered by the user with the configuration lock (such as configuration commands) always have priority over commands entered by other users.

Parser Concurrency and Locking Improvements

In order to overcome the following limitations posed by the Exclusive Configuration Change Access feature, the Parser Concurrency and Locking Improvements feature was introduced in Cisco IOS Release 12.2(33)SRE:

  • The Exclusive Configuration Change Access feature locks the configuration to other users. The lock is automatically released when the lock holder exits from the configuration mode. Any other user in the configuration mode will be returned to the EXEC mode when the lock is acquired. Also, any user can execute the clearconfigurationlock command and forcibly remove the lock and allow normal access to all users.

  • The router can reload when multiple write processes belonging to the same client simultaneously access the Cisco IOS configurations in a shared mode.

  • The router can reload when EXEC commands concurrently access the data structure.

Effective from Cisco IOS Release 12.2(33)SRE, the Concurrency and Locking Improvements feature is the primary locking mechanism used to prevent concurrent configuration of Cisco IOS software by multiple users.

The Parser Concurrency and Locking Improvements feature provides a common interface that ensures that exclusive access is granted to the requested process and prevents others from concurrently accessing the Cisco IOS configuration. It allows access only to the user holding the lock and prevents other clients from accessing the configuration.

Effective from Cisco IOS Release 12.2(33)SRE, the configurationmodeexclusive {auto | manual} command will not be available to enable single-user access functionality for the Cisco IOS CLI. Use the parsercommandserializer command to enable configuration access only to the users holding the lock and prevent other clients from accessing the configuration.

How to Configure Configuration Exclusive Confguration Change-Access and Access Session Locking

Enabling Exclusive Configuration Change Access and Access Session Locking


Note

Effective with Cisco IOS Release 12.2(33)SRE, the Exclusive Configuration Change Access and Access Session Locking feature is not available in Cisco IOS software. Use the Parser Concurrency and Locking Improvements feature instead of this feature. See the “Enabling Parser Concurrency and Locking Improvements” section for more information.

Perform this task to enable the Exclusive Configuration Change Access and Access Session Locking feature.
SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    configuration mode exclusive

    4.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example: 
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2 configure terminal


    Example: 
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 configuration mode exclusive


    Example: 
    Router(config)# configuration mode exclusive
     

    Enables exclusive configuration change access (configuration lock feature).

    • When the command is enabled, configuration sessions are performed in single-user (exclusive) mode.

     
    Step 4 end


    Example: 
    Router(config)# end
     

    Ends your configuration session and returns the CLI to privileged EXEC mode.

     

    Obtaining Exclusive Configuration Change Access

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    configure terminal lock

      4.    Configure the system by entering your changes to the running configuration.

      5.    Do one of the following:

      • end
      • or
      • exit


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example: 
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 configure terminal


      Example: 
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3 configure terminal lock


      Example: 
      Router(config)# configure terminal lock
       

      (Optional) Locks the Cisco IOS software in exclusive (single-user) mode.

      • This command can be used only if you have previously enabled configuration locking by using the configuration mode exclusive command.

      • This command is available in Cisco IOS Release 12.3(14)T or later releases.

       
      Step 4 Configure the system by entering your changes to the running configuration.  

      --

       
      Step 5Do one of the following:
      • end
      • or
      • exit


      Example: 
      Router(config)# end


      Example:


      Example: 
      Router(config)# exit
       

      Ends your configuration session, automatically releases the session lock obtained in Step 1, and exits to privileged EXEC mode.

      Note   

      Either the end command, the exit command, or the Ctrl-Z key combination releases the configuration lock. Use of the end command is recommended.

       

      Enabling Parser Concurrency and Locking Improvements

      Perform this task to enable configuration access only to the users holding a configuration lock and to prevent other clients from accessing the running configuration.


      Note

      The Parser Cconcurrency and Locking Improvements feature does not allow two or more processes to exist simultaneously within the critical section of Cisco IOS configurations.

      This feature flags a command to prevent its serialization if an excessive amount of time is required to generate its output or if its use produces more than 10 kilobytes of output. Examples of commands that would not be serialized are the showterminal and showrunning-config commands.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    parser command serializer

        4.    exit


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2 configure terminal


        Example:
        Router# configure terminal
         

        Enters global configuration mode.

         
        Step 3 parser command serializer


        Example:
        Router(config)# parser command serializer
         

        Introduces an exclusive lock to serialize access to Cisco IOS configurations.

         
        Step 4 exit


        Example:
        Router(config)# exit
         

        (Optional) Exits global configuration mode.

         

        Monitoring and Troubleshooting Configuration Locking

        Perform either or both steps in this task to monitor or troubleshoot the Exclusive Configuration Change Access and Access Session Locking feature.

        SUMMARY STEPS

          1.    show configuration lock

          2.    debug configuration lock


        DETAILED STEPS
          Step 1   show configuration lock

          Use this command to display the status and details of any current configuration locks, including the owner, user, terminal, lock state, and lock class.

          If you cannot enter global configuration mode, you can use this command to determine if the configuration session is locked by another user, and who that user is.



          Example:

          Step 2   debug configuration lock

          Use this command to enable debugging of Cisco IOS configuration locks (exposed class locks or rollback class locks):



          Example: 
          Router# debug configuration lock
 
Session1 from console
==========================
Router# configure terminal lock 
Configuration mode locked exclusively. The lock will be cleared once you exit out of configuration mode using end/exit
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#
Parser : LOCK REQUEST in EXCLUSIVE mode
Parser: <configure terminal lock> - Config. Lock requested by process <3> client <PARSER Client>
Parser: <configure terminal lock> - Config. Lock acquired successfully !
Router(config)#

          Configuration Examples for Locking the Configuration

          Configuring an Exclusive Lock in Auto Mode Example

          The following example shows how to enable the exclusive lock in auto mode for single-user auto configuration mode using the configurationmodeexclusive command. Once the Cisco IOS configuration file is locked exclusively, you can verify this configuration by using the showconfigurationlockcommand. 

          Router# configure terminal 
Router(config)# 
Router(config)# exit 
Router# configure terminal 
! Locks configuration mode exclusively.
Router# show configuration lock
Parser Configure Lock
Owner PID        :  10
User             :  User1
TTY              :  3
Type             :  EXCLUSIVE
State            :  LOCKED
Class            :  Exposed 
Count            :  0 
Pending Requests :  0 
User debug info  :  0

          Configuring an Exclusive Lock in Manual Mode Example

          Configuring Parser Concurrency and Locking Improvements Example

          The following example shows how to enable the Parser Concurrency and Locking Improvements feature by using the parsercommandserializer command:

          Router# configure terminal
Router(config)# parser command serializer
Router(config)# exit

          Additional References

          The following sections provide references related to locking the configuration.

          Related Documents

          Related Topic

          Document Title

          Commands for managing configuration files

          Cisco IOS Configuration Management Command Reference

          Information about managing configuration files

          Managing Configuration Files

          Standards

          Standard

          Title

          No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

          --

          MIBs

          MIB

          MIBs Link

          No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

          To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

          http:/​/​www.cisco.com/​go/​mibs

          RFCs

          RFC

          Title

          No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

          --

          Technical Assistance

          Description

          Link

          The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

          To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

          Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

          http:/​/​www.cisco.com/​techsupport

          Feature Information for Exclusive Configuration Change Access and Access Session Locking

          The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

          Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.
          Table 1 Feature Information for Exclusive Configuration Change Access and Access Session Locking

          Feature Name

          Releases

          Feature Information

          Exclusive Configuration Change Access and Access Session Locking

          12.3(14)T 12.0(31)S 12.2(33)SRA 12.4(11)T 12.2(33)SXH 12.2(33)SB

          The Exclusive Configuration Change Access feature (also called the “Configuration Lock” feature) allows you to have exclusive change access to the Cisco IOS running configuration, preventing multiple users from making concurrent configuration changes.

          The Access Session Locking addition to this feature extends the Exclusive Configuration Change Access feature such that show and debug commands entered by the user holding the configuration lock always have execution priority;show and debug commands entered by other users are allowed to run only after the processes initiated by the configuration lock owner have finished.

          The Exclusive Configuration Change Access feature is complementary with the locking mechanism for the Configuration Replace and Configuration Rollback feature (“rollback lock”).

          The Configuration Lock feature feature was integrated into Release 12.0S, and the Access Session Locking feature extension was implemented. The configuration mode exclusivecommand was extended to include the following keyword options: config_wait, expire, interleave, lock-show, retry_wait, and terminate. The output of the show configuration lockcommand was improved.

          The extended feature was integrated into Releases 12.2(33)SRA, 12.4(11)T, 12.2(33)SXH, and 12.2(33)SB.

          The following sections provide information about this feature:

          • Information About Locking the Configuration

          • How to Configure Configuration Lock

          The following commands were introduced or modified: clear configuration lock, configuration mode exclusive, and configure terminal lock.

          Parser Concurrency and Locking Improvements

          12.2(33)SRE

          15.1(1)T

          The Parser Concurrency and Locking Improvements feature provides a common interface that ensures that exclusive access is granted to the requested process and prevents others from concurrently accessing the Cisco IOS configuration. It allows access only to the user holding the lock and prevents other clients from accessing the configuration.

          The following sections provide information about this feature:

          • Parser Concurrency and Locking Improvements

          • Enabling Parser Concurrency and Locking Improvements

          The following commands were introduced or modified: parser command serializer and test parser session-lock.