IP Routing: OSPF Configuration Guide, Cisco IOS Release 15S
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OSPF NSR

Last Updated: November 26, 2012

The OSPF NSR feature allows a device with redundant Route Processors (RPs) to maintain its Open Shortest Path First (OSPF) state and adjacencies across planned and unplanned RP switchovers. It does this by checkpointing state information from OSPF on the active RP to the standby RP. Later, following a switchover to the standby RP, OSPF can use this checkpointed information to continue operation without interruption.

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 at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for OSPF NSR

  • OSPF NSR is available for platforms with redundant RPs running Cisco IOS Release 15.1(2)S or later releases.

Restrictions for OSPF NSR

  • OSPF nonstop routing (NSR) can significantly increase the memory used by OSPF during certain phases of its operation. CPU usage also can be increased. You should be aware of device memory capacity and estimate the likely memory requirements of OSPF NSR. For more information, see the Configuring OSPF NSR task. For devices in which memory and CPU are constrained, you might want to consider using OSPF NSF instead. For more information, see NSF--OSPF (RFC 3623 OSPF Graceful Restart).
  • A switchover from the active to the standby RP can take several seconds (depending on the hardware platform), and during this time OSPF is unable to send Hello packets. As a result, configurations that use small OSPF dead intervals might not be able to maintain adjacencies across a switchover.

Information About OSPF NSR

OSPF NSR Functionality

Although OSPF NSR serves a similar function to OSPF NSF, it works differently. With NSF, OSPF on the newly active standby RP initially has no state information, so it uses extensions to the OSPF protocol to recover its state from neighboring OSPF devices. For this to work, the neighbors must support the NSF protocol extensions and be willing to act as "helpers" to the restarting device. They must also continue forwarding data traffic to the restarting device while this recovery is taking place.

With NSR, by contrast, the device performing the switchover preserves its state internally, and in most cases the neighbors are unaware that anything has happened. Because no assistance is needed from neighboring devices, NSR can be used in situations where NSF cannot; for example, in networks where not all the neighbors implement the NSF protocol extensions, or where network topology changes during the recovery can make NSF unreliable.

How to Configure OSPF NSR

Configuring OSPF NSR


Note
NSR adds a single new line, "nsr," to the OSPF router mode configuration. Devices that do not support NSR, for whatever reason, will not accept this command.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router ospf process-id

4.    n sr

5.    end

6.    show ip ospf [ process-id ] nsr [[ objects ]|[ statistics ]]


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
router ospf process-id


Example:

Device(config)# router ospf 109

 

Places the device in router configuration mode and configures an OSPF routing process.

 
Step 4
n sr


Example:

Device(config-router)# nsr

 

Configures NSR.

 
Step 5
end


Example:

Device(config-router)# end

 

Exits router configuration mode and returns to privileged EXEC mode.

 
Step 6
show ip ospf [ process-id ] nsr [[ objects ]|[ statistics ]]


Example:

Device# show ip ospf 109 nsr

 

Displays OSPF NSR status information.

 

Troubleshooting Tips

OSPF NSR can increase the amount of memory used by the OSPF device process. To determine how much memory OSPF is currently using without NSR, you can use the show processes and show processes memory commands: 

Device# show processes
 | include OSPF
 276 Mwe  133BE14         1900       1792    1060 8904/12000  0 OSPF-1 Router
 296 Mwe  133A824           10        971      10 8640/12000  0 OSPF-1 Hello

Process 276 is the OSPF device process that is to be checked. The show processes memory command is used to display its current memory use: 

Device# show processes memory 276
Process ID: 276
Process Name: OSPF-1 Router
Total Memory Held: 4454800 bytes

In this case, OSPF is using 4,454,800 bytes, or approximately 4.5 megabytes (MB). OSPF NSR could double this amount of memory for brief periods, so make sure the device has at least 5 MB of free memory before enabling OSPF NSR.

Configuration Examples for OSPF NSR

Example: Configuring OSPF NSR

The following example shows how to configure OSPF NSR: 

Device> enable
Device# configure terminal
Device(config)# router ospf 1
Device(config-router)# nsr
Device(config-router)# end
Device# show ip ospf 1 nsr
Standby RP
 Operating in duplex mode
 Redundancy state: STANDBY HOT
 Peer redundancy state: ACTIVE
 ISSU negotation complete
 ISSU versions compatible
Routing Process "ospf 1" with ID 10.1.1.100
 NSR configured
 Checkpoint message sequence number: 3290
 Standby synchronization state: synchronized
 Bulk sync operations:  1
 Last sync start time:  15:22:48.971 UTC Fri Jan 14 2011
 Last sync finish time: 15:22:48.971 UTC Fri Jan 14 2011
 Last sync lost time:   -
 Last sync reset time:  -
 LSA Count: 2, Checksum Sum 0x00008AB4

The output shows that OSPF NSR is configured and that OSPF on the standby RP is fully synchronized and ready to continue operation should the active RP fail or if a manual switchover is performed.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

OSPF commands

Cisco IOS IP Routing: OSPF Command Reference

Configuring IETF NSF or Cisco NSF

NSF--OSPF (RFC 3623 OSPF Graceful Restart)

Standards

Standard

Title

None

--

MIBs

MIB

MIBs Link

None

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

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

RFCs

RFC

Title

RFC 2328

OSPF Version 2

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for OSPF NSR

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 www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1Feature Information for OSPF NSR

Feature Name

Releases

Feature Information

OSPF NSR

15.1(2)S

The OSPF NSR feature allows a router with redundant Route Processors to maintain its OSPF state and adjacencies across planned and unplanned RP switchovers.

The following commands were introduced or modified: nsr, show ip ospf nsr.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2012 Cisco Systems, Inc. All rights reserved.