NSF SSO--MPLS TE and RSVP Graceful Restart

The NSF/SSO--MPLS TE and RSVP Graceful Restart feature allows a Route Processor (RP) to recover from disruption in control plane service without losing its Multiprotocol Label Switching (MPLS) forwarding state.

Cisco nonstop forwarding (NSF) with stateful switchover (SSO) provides continuous packet forwarding, even during a network processor hardware or software failure. In a redundant system, the secondary processor recovers control plane service during a critical failure in the primary processor. SSO synchronizes the network state information between the primary and the secondary processor.

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 NSF SSO--MPLS TE and RSVP Graceful Restart

  • Configure Resource Reservation Protocol (RSVP) graceful restart in full mode.

  • Configure RSVP graceful restart on all interfaces of the neighbor that you want to be restart-capable.

  • Configure the redundancy mode as SSO. See the Stateful Switchover feature module for more information.

  • Enable NSF on the routing protocols running among the provider routers (P), provider edge (PE) routers, and customer edge (CE) routers. The routing protocols are as follows:
    • Border Gateway Protocol (BGP)
    • Open Shortest Path First (OSPF)
    • Intermediate System-to-Intermediate System (IS-IS)

See the Cisco Nonstop Forwarding feature module for more information.

  • Enable MPLS.

  • Configure traffic engineering (TE).

Restrictions for NSF SSO--MPLS TE and RSVP Graceful Restart

  • RSVP graceful restart supports node failure only.

  • Unnumbered interfaces are not supported.

  • You cannot enable RSVP fast reroute (FRR) hello messages and RSVP graceful restart on the same router.

  • You cannot enable primary one-hop autotunnels, backup autotunnels, or autotunnel mesh groups on a router that is also configured with SSO and Route Processor Redundancy Plus (RPR+). This restriction does not prevent an MPLS TE tunnel that is automatically configured by TE autotunnel from being successfully recovered if any midpoint router along the label-switched path (LSP) of the router experiences an SSO.

  • MPLS TE LSPs that are fast reroutable cannot be successfully recovered if the LSPs are FRR active and the Point of Local Repair (PLR) router experiences an SSO.

  • When you configure RSVP graceful restart, you must use the neighbor’s interface IP address.

Information About NSF SSO--MPLS TE and RSVP Graceful Restart

Overview of MPLS TE and RSVP Graceful Restart

RSVP graceful restart allows RSVP TE-enabled nodes to recover gracefully following a node failure in the network such that the RSVP state after the failure is restored as quickly as possible. The node failure may be completely transparent to other nodes in the network.

RSVP graceful restart preserves the label values and forwarding information and works with third-party or Cisco routers seamlessly.

RSVP graceful restart depends on RSVP hello messages to detect that a neighbor went down. Hello messages include Hello Request or Hello Acknowledgment (ACK) objects between two neighbors.

As shown in the figure below, the RSVP graceful restart extension to these messages adds an object called Hello Restart_Cap, which tells neighbors that a node may be capable of recovering if a failure occurs.



The Hello Restart_Cap object has two values: the restart time, which is the sender’s time to restart the RSVP_TE component and exchange hello messages after a failure; and the recovery time, which is the desired time that the sender wants the receiver to synchronize the RSVP and MPLS databases.

In the figure above, RSVP graceful restart help neighbor support is enabled on Routers 1 and 3 so that they can help a neighbor recover after a failure, but they cannot perform self recovery. Router 2 has full SSO help support enabled, meaning it can perform self recovery after a failure or help its neighbor to recover. Router 2 has two RPs, one that is active and one that is standby (backup). A TE LSP is signaled from Router 1 to Router 4.

Router 2 performs checkpointing; that is, it copies state information from the active RP to the standby RP, thereby ensuring that the standby RP has the latest information. If an active RP fails, the standby RP can take over.

Routers 2 and 3 exchange periodic graceful restart hello messages every 10,000 milliseconds (ms) (10 seconds), and so do Routers 2 and 1 and Routers 3 and 4. Assume that Router 2 advertises its restart time = 60,000 ms (60 seconds) and its recovery time = 60,000 ms (60 seconds) as shown in the following example: 

23:33:36: Outgoing Hello:
23:33:36:   version:1 flags:0000 cksum:883C ttl:255 reserved:0 length:32
23:33:36:  HELLO                type HELLO REQUEST length 12:
23:33:36:   Src_Instance: 0x6EDA8BD7, Dst_Instance: 0x00000000
23:33:36:  RESTART_CAP          type 1 length 12:
23:33:36:   Restart_Time: 0x0000EA60, Recovery_Time: 0x0000EA60

Router 3 records this into its database. Also, both neighbors maintain the neighbor status as UP. However, Router 3’s control plane fails at some point (for example, a primary RP failure). As a result, RSVP and TE lose their signaling information and states although data packets continue to be forwarded by the line cards.

When Router 3 declares communication with Router 2 lost, Router 3 starts the restart time to wait for the duration advertised in Router 2’s restart time previously recorded (60 seconds). Routers 1 and 2 suppress all RSVP messages to Router 3 except hellos. Router 3 keeps sending the RSVP PATH and RESV refresh messages to Routers 4 and 5 so that they do not expire the state for the LSP; however, Routers 1 and 3 suppress these messages for Router 2.

When Routers 1 and 3 receive the hello message from Router 2, Routers 1 and 3 check the recovery time value in the message. If the recovery time is 0, Router 3 knows that Router 2 was not able to preserve its forwarding information, and Routers 1 and 3 delete all RSVP state that they had with Router 2.

If the recovery time is greater than 0, Router 1 sends Router 2 PATH messages for each LSP that it had previously sent through Router 2. If these messages were previously refreshed in summary messages, they are sent individually during the recovery time. Each of these PATH messages includes a Recovery_Label object containing the label value received from Router 2 before the failure.

When Router 3 receives a PATH message from Router 2, Router 3 sends a RESV message upstream. However, Router 3 suppresses the RESV message until it receives a PATH message. When Router 2 receives the RESV message, it installs the RSVP state and reprograms the forwarding entry for the LSP.

Benefits of MPLS TE and RSVP Graceful Restart

State Information Recovery

RSVP graceful restart allows a node to perform self recovery or to help its neighbor recover state information when there is an RP failure or the device has undergone an SSO.

Session Information Recovery

RSVP graceful restart allows session information recovery with minimal disruption to the network.

Increased Availability of Network Services

A node can perform a graceful restart to help itself or a neighbor recover its state by keeping the label bindings and state information, thereby providing a faster recovery of the failed node and not affecting currently forwarded traffic.

How to Configure NSF SSO--MPLS TE and RSVP Graceful Restart

Enabling RSVP Graceful Restart Globally

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip rsvp signalling hello graceful-restart mode (help-neighbor| full)

    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 ip rsvp signalling hello graceful-restart mode (help-neighbor| full)


    Example:
    Router(config)# ip rsvp signalling hello graceful-restart mode full
     

    Enables RSVP TE graceful restart capability on an RP.

    • Enter the help-neighbor keyword to enable a neighboring router to restart after a failure.

    • Enter the fullkeyword to enable a router to perform self recovery or to help a neighbor recover after a failure.

     
    Step 4 exit


    Example:
    Router(config)# exit
     

    (Optional) Returns to privileged EXEC mode.

     

    Enabling RSVP Graceful Restart on an Interface

    You must repeat this procedure for each of the neighbor router’s interfaces.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type slot / subslot / port [. subinterface-number]

      4.    Repeat Step 3 as needed to configure additional interfaces.

      5.    ip rsvp signalling hello graceful-restart neighbor ip-address

      6.    Repeat Step 5 as needed to configure additional IP addresses on a neighbor router's interfaces.

      7.    exit

      8.    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 interface type slot / subslot / port [. subinterface-number]


      Example:
      Router(config)# interface POS 1/0/0
       

      Configures the interface type and number and enters interface configuration mode.

       
      Step 4 Repeat Step 3 as needed to configure additional interfaces.  

      (Optional) Configures additional interfaces.

       
      Step 5 ip rsvp signalling hello graceful-restart neighbor ip-address


      Example:
      Router(config-if)# ip rsvp signalling hello graceful-restart neighbor 10.0.0.0
       

      Enables support for RSVP graceful restart on routers helping their neighbors recover TE tunnels following SSO.

      Note   

      The IP address must be that of the neighbor’s interface.

       
      Step 6 Repeat Step 5 as needed to configure additional IP addresses on a neighbor router's interfaces.  

      (Optional) Configures additional IP addresses on a neighbor router’s interfaces.

       
      Step 7 exit


      Example:
      Router(config-if)# exit
       

      Exits interface configuration mode and returns to global configuration mode.

       
      Step 8 exit


      Example:
      Router(config)# exit
       

      (Optional) Exits global configuration mode and returns to privileged EXEC mode.

       

      Setting a DSCP Value for RSVP Graceful Restart

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    ip rsvp signalling hello graceful-restart dscp num

        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 ip rsvp signalling hello graceful-restart dscp num


        Example:
        Router(config)# ip rsvp signalling hello graceful-restart dscp 30
         

        Sets a DSCP value on a router with RSVP graceful restart enabled.

         
        Step 4 exit


        Example:
        Router(config)# exit
         

        (Optional) Returns to privileged EXEC mode.

         

        Setting a Value to Control the Refresh Interval for RSVP Hello Messages

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    ip rsvp signalling hello graceful-restart refresh interval interval-value

          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 ip rsvp signalling hello graceful-restart refresh interval interval-value


          Example:
          Router(config)# ip rsvp signalling hello graceful-restart refresh interval  5000
           

          Sets the value to control the request interval in graceful restart hello messages. This interval represents the frequency at which RSVP hello messages are sent to a neighbor; for example, one hello message is sent per each interval.

          Note   

          If you change the default value for this command and you also changed the RSVP refresh interval using the ip rsvp signalling refresh interval command, ensure that the value for the ip rsvp signalling hello graceful-restart refresh intervalcommand is less than the value for the ip rsvp signalling hello refresh interval command. Otherwise, some or all of the label-switched paths (LSPs) may not be recovered after an SSO has occurred.

           
          Step 4 exit


          Example:
          Router(config)# exit
           

          (Optional) Returns to privileged EXEC mode.

           

          Setting a Value to Control the Missed Refresh Limit for RSVP Graceful Restart Hello Acknowledgements

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    ip rsvp signalling hello graceful-restart refresh misses msg-count

            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 ip rsvp signalling hello graceful-restart refresh misses msg-count


            Example:
            Router(config)# ip rsvp signalling hello graceful-restart refresh misses 5
             

            Specifies how many sequential RSVP TE graceful restart hello acknowledgments (ACKs) a node can miss before the node considers communication with its neighbor lost.

            Note   

            If you change the default value for this command and you are also using the ip rsvp signalling hello refresh missescommand, ensure that the value for the ip rsvp signalling hello graceful-restart refresh missescommand is less than the value for the ip rsvp signalling hello refresh misses command. Otherwise, some or all of the LSPs may not be recovered after an SSO has occurred.

             
            Step 4 exit


            Example:
            Router(config)# exit
             

            (Optional) Returns to privileged EXEC mode.

             

            Verifying the RSVP Graceful Restart Configuration

            SUMMARY STEPS

              1.    enable

              2.    show ip rsvp hello graceful-restart

              3.    exit


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 enable


              Example:
              Router> enable
               

              (Optional) Enables privileged EXEC mode.

              • Enter your password if prompted.

               
              Step 2 show ip rsvp hello graceful-restart


              Example:
              Router# show ip rsvp hello graceful-restart
               

              Displays information about the status of RSVP graceful restart and related parameters.

               
              Step 3 exit


              Example:
              Router# exit
               

              (Optional) Returns to user EXEC mode.

               

              Configuration Examples for NSF SSO--MPLS TE and RSVP Graceful Restart

              Example Configuring NSF SSO--MPLS TE and RSVP Graceful Restart

              In the following example, RSVP graceful restart is enabled globally and on a neighbor router’s interfaces as shown in the figure below. Related parameters, including a DSCP value, a refresh interval, and a missed refresh limit are set. 



              enable
configure terminal
ip rsvp signalling hello graceful-restart mode full
interface POS 1/0/0
 ip rsvp signalling hello graceful-restart neighbor 10.0.0.1 
 ip rsvp signalling hello graceful-restart neighbor 10.0.0.2 
 exit
ip rsvp signalling hello graceful-restart dscp 30
ip rsvp signalling hello graceful-restart refresh interval 50000
ip rsvp signalling hello graceful-restart refresh misses 5 
exit

              Example Verifying the NSF SSO--MPLS TE and RSVP Graceful Restart Configuration

              Router# show ip rsvp hello graceful-restart
Graceful Restart: Enabled (full mode)
  Refresh interval: 10000 msecs
  Refresh misses: 4
  DSCP:0x30
  Advertised restart time: 30000 msecs
  Advertised recovery time: 120000 msecs
  Maximum wait for recovery: 3600000 msecs

              Additional References

              Related Documents

              Related Topic

              Document Title

              Cisco IOS commands

              Cisco IOS Master Commands List, All Releases

              RSVP commands: complete command syntax, command mode, defaults, usage guidelines, and examples

              Cisco IOS Quality of Service Solutions Command Reference

              Quality of service (QoS) classification

              Classification Overview

              Stateful switchover

              Stateful Switchover

              Cisco nonstop forwarding

              Information about Cisco Nonstop Forwarding

              RSVP hello state timer

              MPLS Traffic Engineering: RSVP Hello State Timer

              Standards

              Standards

              Title

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

              --

              MIBs

              MIBs

              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 software releases, and feature sets, use Cisco MIB Locator found at the following URL:

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

              RFCs

              RFCs

              Title

              RFC 3209

              RSVP-TE: Extensions to RSVP for LSP Tunnels

              RFC 3473

              Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource Reservation Protocol-Traffic Engineering (RSVP-TE) Extensions

              RFC 4558

              Node-ID Based Resource Reservation Protocol (RSVP) Hello: A Clarification Statement

              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 NSF SSO--MPLS TE and RSVP Graceful Restart

              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 1 Feature Information for NSF/SSO--MPLS TE and RSVP Graceful Restart

              Feature Name

              Releases

              Feature Information

              NSF/SSO--MPLS TE and RSVP Graceful Restart

              Cisco IOS XE Release 3.1S

              Cisco IOS XE Release 3.5S

              The NSF/SSO--MPLS TE and RSVP Graceful Restart feature allows a Route Processor (RP) to recover from disruption in control plane service without losing its Multiprotocol Label Switching (MPLS) forwarding state.

              Cisco nonstop forwarding (NSF) with stateful switchover (SSO) provides continuous packet forwarding, even during a network processor hardware or software failure. In a redundant system, the secondary processor recovers control plane service during a critical failure in the primary processor. SSO synchronizes the network state information between the primary and the secondary processor.

              In Cisco IOS XE Release 3.1S, this feature was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.

              The following commands were introduced or modified: clear ip rsvp high-availability counters, debug ip rsvp high-availability, debug ip rsvp sso, debug mpls traffic-eng ha sso, ip rsvp signalling hello graceful-restart dscp, ip rsvp signalling hello graceful-restart mode, ip rsvp signalling hello graceful-restart mode help-neighbor, ip rsvp signalling hello graceful-restart neighbor, ip rsvp signalling hello graceful-restart refresh interval, ip rsvp signalling hello graceful-restart refresh misses, show ip rsvp counters, show ip rsvp counters state teardown, show ip rsvp hello, show ip rsvp hello client lsp detail, show ip rsvp hello client lsp summary, show ip rsvp hello client neighbor detail, show ip rsvp hello client neighbor summary, show ip rsvp hello graceful-restart, show ip rsvp hello instance detail, show ip rsvp hello instance summary, show ip rsvp high-availability counters, show ip rsvp high-availability database, show ip rsvp high-availability summary.

              MPLS TE--RSVP Graceful Restart 12.0S--12.2S Interop

              Cisco IOS XE Release 3.5S

              In Cisco IOS XE Release 3.5S, this feature was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.

              MPLS TE— Autotunnel/Automesh SSO Coexistence

              Cisco IOS XE Release 3.5S

              In Cisco IOS XE Release 3.5S, this feature was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.

              Glossary

              DSCP --differentiated services code point. Six bits in the IP header, as defined by the Internet Engineering Task Force (IETF). These bits determine the class of service provided to the IP packet.

              Fast Reroute --A mechanism for protecting Multiprotocol Label Switching (MPLS) traffic engineering (TE) label switched paths (LSPs) from link and node failure by locally repairing the LSPs at the point of failure, allowing data to continue to flow on them while their headend routers attempt to establish end-to-end LSPs to replace them. Fast reroute (FRR) locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or nodes.

              graceful restart --A process for helping a Route Processor (RP) restart after a node failure has occurred.

              headend --The router that originates and maintains a given label switched path (LSP). This is the first router in the LSP’s path.

              hello instance --A mechanism that implements the Resource Reservation Protocol (RSVP) hello extensions for a given router interface address and remote IP address. Active hello instances periodically send hello request messages, expecting Hello ACK messages in response. If the expected ACK message is not received, the active hello instance declares that the neighbor (remote IP address) is unreachable (that is, it is lost). This can cause LSPs crossing this neighbor to be fast rerouted.

              IGP --Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).

              ISSU --In Service Software Upgrade. Software upgrade without service interruption.

              label --A short, fixed-length data identifier that tells switching nodes how to forward data (packets or cells).

              LSP --label switched path. A configured connection between two routers, in which Multiprotocol Label Switching (MPLS) is used to carry packets.

              MPLS --Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. MPLS enables routers at the edge of a network to apply labels to packets (frames). ATM switches or existing routers in the network core can switch packets according to the labels.

              RSVP --Resource Reservation Protocol. A protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams they want to receive.

              state --Information that a router must maintain about each label switched path (LSP). The information is used for rerouting tunnels.

              tailend --The router upon which a label switched path (LSP) is terminated. This is the last router in the LSP’s path.

              TE --traffic engineering. The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been used.