Configuring OSPF Graceful Restart Support

The OSPF GR (Graceful Restart) support helps in increasing the availability of your network by allowing OSPF routers to stay on the forwarding path even if their OSPF software is restarted. The restarting router informs the neighbors about its capability to restart gracefully. The neighbors wait for a certain time interval before recalculating routes and diverting traffic. During this time interval, the OSPF software can be started up again and brought to its original state. The end result is that the traffic remains undisturbed.

OSPF supports two types of graceful restart:
  • Planned
  • Unplanned
Parent topic: Configuring OSPF

Enabling / Disabling Graceful Restart Support

This configuration makes an OSPF router to support GR functionality. This section lists CLI configurations for enabling and disabling GR support on an OSPF router.

  1. To enable the graceful support for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Enable opaque functionality.
    iS5comm (config-router)# capability opaque
    • Enable GR support. This configuration enables ISS1 to support both planned an un-planned restart.
    iS5comm (config-router)# nsf ietf restart-support
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the graceful restart related configuration in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)
    Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 120
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Unknown
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds
  3. Execute the no form of the command to disable GR support.

    Type the following:

    iS5comm(config-router)# no nsf ietf restart-support

Configuring Graceful Restart Interval

Graceful restart (GR) interval is the period of time during which the router can reacquire OSPF neighbors that are fully operational prior to the restart. The value ranges between 1 and 1800 seconds. The value is provided as an intimation of the grace period to all neighbors.

  1. To enable the graceful restart interval for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the graceful restart timeout interval as 200 seconds.
    iS5comm(config-router)# nsf ietf restart-interval 200
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the graceful restart related configuration in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Unknown
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds
  3. Execute the no form of the command to reset the graceful restart interval to default value (120 seconds.

    Type the following:

    iS5comm(config-router)# no nsf ietf restart-interval

Configuring Grace LSA Acknowledgement Required

This configuration enables Grace Ack Required state in the restarting router. If the Grace Ack Required state is enabled, then the Grace -LSAs sent by this router need to be acknowledged by peers. By default, this state is enabled in the restarting router.

  1. To enable Grace LSA Ack required state for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the Grace-LSA Ack required state as enabled in ISS1.
    iS5comm(config-router)# nsf ietf grace lsa ack required
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Unknown
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds
  3. Execute the no form of the command to reset the graceful restart interval to default value (120 seconds.

    Type the following:

    iS5comm(config-router)# no nsf ietf restart-interval

Configuring Grace LSA Retransmission Count

This section lists CLI configurations for configuring the maximum number of retransmissions for unacknowledged GraceLSA. This value ranges between 0 and 180.

  1. To configure Grace-LSA retransmission count to 100 for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the Grace LSA retransmission count as 100 in ISS1.
    iS5comm(config-router)# nsf ietf grlsa retrans count 100
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 100
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Unknown
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds

Configuring Graceful Restart Reason

This section lists the configuration to set the incidence for which GR feature is applied. GR reason can be unknown, softwareRestart, swReloadUpgrade, and switchToRedundant. By default, restart reason is set as unknown.

  1. To enable Grace LSA Ack required state for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the restart reason as software Restart in ISS1.
    iS5comm(config-router)# nsf ietf restart-reason softwareRestart
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)
    Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Software Restart
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds

Configuring Graceful Restart Helper Support

The neighbors of the restarting routers can act as helpers depending on their helper support configurations. This section lists the CLI configurations related to helper support.

Enabling / Disabling Graceful Restart Helper Support

The neighbors of the restarting routers acts as helper during the graceful restart based on their support configurations. By default the routers are enabled to act as a helping neighbor and can support all four types of restart reasons such as unknown, softwareRestart, swReloadUpgrade and switchToRedundant

  1. To enable Grace LSA Ack required state for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the helper support as softwareRestart in ISS1.
    iS5comm(config-router)# nsf ietf helper-support softwareRestart
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)
    Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Software Restart
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds
  3. Execute the no form of the command to disable the helper support in the router (ISS1).

    Type the following:

    iS5comm(config-router)# no nsf ietf helper-support softwareRestart

Configuring Grace Time Limit for the Helper

The neighbors of the restarting routers acts as helper during the graceful restart based on their support configurations. By default the routers are enabled to act as a helping neighbor and can support all four types of restart reasons such as unknown, softwareRestart, swReloadUpgrade and switchToRedundant

  1. To enable Grace LSA Ack required state for the switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Enable the helper support in ISS1.
    iS5comm(config-router)# nsf ietf helper-support softwareRestart
    • Configure the helper grace time limit as 100 in ISS1.
    iS5comm(config-router)# nsf ietf helper gracetimelimit 100
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)
    Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Software Restart
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 100
    Strict LSA checking State Is:Disabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds

Configuring Strict-LSA Check Option in Helper

The strict LSA check option allows the helper to terminate the graceful restart, once a changed LSA that causes flooding during the restart process is detected.

  1. To configure the strict-LSA check option for the helping switch (ISS1):

    Type the following:

    • Enter the Global Configuration Mode in ISS1.
    iS5comm# configure terminal
    • Enable OSPF globally in the switch and enter the Router Configuration mode.
    iS5comm(config)# router ospf
    • Configure the OSPF router ID.
    iS5comm (config-router)# router-id 10.10.2.1
    • Configure the helper support as softwareRestart in ISS1.
    iS5comm(config-router)# nsf ietf helper-support softwareRestart
    • Enable the strict LSA check option in ISS1.
    iS5comm(config-router)# nsf ietf helper strict-lsa-checking
    • Exit from the Router Configuration mode.
    iS5comm (config-router)# exit
  2. View the configuration done in ISS1.

    Type the following:

    iS5comm# show ip ospf
    OSPF Router with ID (10.10.2.1) (Vrf  default)
    Supports multiple TOS routes
    ABR Type supported is Standard ABR
    Number of Areas in this router is 1
    Area is 0.0.0.0
    Number of interfaces in this area is 0
     SPF algorithm executed 0 times
    Planned & Unplanned Non-Stop Forwarding enabled
    Restart-interval limit: 200
    Grace LSA Retransmission Count: 2
    Helper Grace LSA ACK :Required
    Restart Reason is:
    Software Restart
    Helper is Giving Support for:
    Unknown
    Software Restart
    Software Reload/Upgrade
    Switch To Redundant
    Helper Grace Time Limit: 0
    Strict LSA checking State Is:Enabled
    Route calculation staggering is enabled
    Route calculation staggering interval is  10 seconds
  3. Execute the no form of the command to disable the strict-LSA check option for the helping switch (ISS1)

    Type the following:

    iS5comm(config-router)# no nsf ietf helper strict-lsa-checking