MPLS Traffic Engineering Path Link and Node Protection Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 1000)
MPLS Traffic Engineering—RSVP Graceful Restart
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MPLS Traffic Engineering—RSVP Graceful Restart

MPLS Traffic Engineering—RSVP Graceful Restart

The MPLS Traffic Engineering—RSVP Graceful Restart feature allows a neighboring Route Processor (RP) to recover from disruption in control plane service (specifically, the Label Distribution Protocol (LDP) component) without losing its Multiprotocol Label Switching (MPLS) forwarding state. This feature has the following benefits:

  • Graceful restart allows a node to recover state information from its neighbor when there is an RP failure or the device has undergone a stateful switchover (SSO).
  • Graceful restart allows session information recovery with minimal disruption to the network.
  • A node can perform a graceful restart to help a neighbor recover its state by keeping the label bindings and state information to provide a quick recovery of the failed node and not affect the traffic that is currently forwarded.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 document.

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 MPLS TE—RSVP Graceful Restart

Perform the following tasks on routers before configuring the MPLS Traffic Engineering—RSVP Graceful Restart feature:

  • Configure the Resource Reservation Protocol (RSVP).
  • Enable MPLS.
  • Configure traffic engineering (TE).
  • Enable graceful restart.

Restrictions for MPLS TE—RSVP Graceful Restart

  • Graceful restart supports node failure only.
  • Cisco recommends that you configure interface hellos only if the neighbor router does not support node hellos.
  • Unnumbered interfaces are not supported.
  • You cannot configure an interface hello for graceful restart and an interface hello for Fast ReRoute or hello state timeout (HST) on the same interface.

Information About MPLS TE—RSVP Graceful Restart

Graceful Restart Operation

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.

A node hello is transmitted when graceful restart is globally configured and the first LSP to the neighbor is created.

Interface hello is an optional configuration. If you configure the graceful restart Hello command on an interface, the interface hello is considered to be an additional hello instance with the neighbor.

The router transmits an interface hello for graceful restart when all of the following conditions are met:

  • Graceful restart is configured globally.
  • Graceful restart is configured on the interface.
  • An LSP to the neighboring router is created and goes over the interface.

Cisco recommends that you use node hellos if the neighbor supports node hellos, and configure interface hellos only if the neighbor router does not support node hellos.

Interface hellos differ from node hellos. as follows:

  • Interface hello —The source address in the IP header of the hello message has an IP address that matches the interface that the Hello message sent out. The destination address in the IP header is the interface address of the neighbor on the other side of the link. A TTL of 1 is used for per-interface hellos as it is destined for the directly-connected neighbor.
  • Node hello —The source address in the IP header of the Hello message includes the TE router ID of the sending router. The destination address of the IP header has the router ID of the neighbor to which this message is sent. A TTL of more than 1 is used.

The figure below shows the graceful restart extension to these messages that an object called Restart_Cap, which tells neighbors that a node, may be capable of restarting if a failure occurs. The time-to-live (TTL) in these messages is set to 255 so that adjacencies can be maintained through alternate paths even if the link between two neighbors goes down.

Figure 1. How Graceful Restart Works

The 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, graceful restart is enabled on Router 1, Router 2, Router 3, and Router 4. For simplicity, assume that all routers are restart capable. A TE label switched path (LSP) is signaled from Router 1 to Router 4.

Router 2 and Router 3 exchange periodic graceful restart hello messages every 10000 ms (10 seconds), and so do Router 2 and Router 1 and Router 3 and Router 4. Assume that Router 2 advertises its restart time as 60000 ms (60 seconds) and its recovery time as 60000 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

Note


The restart and recovery time are shown in bold in the last entry.


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 Route Processor 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 four ACK messages are missed from Router 2 (40 seconds), Router 3 declares communication with Router 2 lost “indicated by LOST” and starts the restart time to wait for the duration advertised in Router 2’s restart time previously and recorded (60 seconds). Router 1 and Router 2 suppress all RSVP messages to Router 3 except hellos. Router 3 keeps sending the RSVP Path and Resv refresh messages to Router 4 and Router 5 so that they do not expire the state for the LSP; however, Router 3 suppresses these messages for Router 2.


Note


A node restarts if it misses four ACKs or its hello src_instance (last source instance sent to its neighbor) changes so that its restart time = 0.


Before the restart time expires, Router 2 restarts and loads its configuration and graceful restart makes the configuration of Router 2 send the hello messages with a new source instance to all the data links attached. However, because Router 2 has lost the neighbor states, it does not know what destination instance it should use in those messages; therefore, all destination instances are set to 0.

When Router 3 sees the hello from Router 2, Router 3 stops the restart time for Router 2 and sends an ACK message back. When Router 3 sees a new source instance value in Router 2’s hello message, Router 3 knows that Router 2 had a control plane failure. Router 2 gets Router 3’s source instance value and uses it as the destination instance going forward.

Router 3 also checks the recovery time value in the hello message from Router 2. If the recovery time is 0, Router 3 knows that Router 2 was not able to preserve its forwarding information and Router 3 deletes all RSVP state that it 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.

How to Configure MPLS TE—RSVP Graceful Restart

Enabling Graceful Restart


Note


It is optional that you configure graceful restart on an interface.


SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    ip rsvp signalling hello graceful-restart mode help-neighbor

    4.    interface type number

    5.    ip rsvp signalling hello graceful-restart

    6.    exit


DETAILED STEPS
      Command or Action Purpose
    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


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

    Sets the number of DSCP hello messages on a neighboring router with restart capability.

     
    Step 4 interface type number


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

    (Optional) Configures the interface type and number and enters interface configuration mode.

     
    Step 5 ip rsvp signalling hello graceful-restart


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

    (Optional) Enables RSVP TE graceful restart capability on a neighboring router.

     
    Step 6 exit


    Example:
    Router(config)# exit 
     

    Exits to privileged EXEC mode.

     

    Setting a DSCP Value

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    ip rsvp signalling hello graceful-restart dscp num

      4.    end


    DETAILED STEPS
        Command or Action Purpose
      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 the number of DSCP hello messages on a graceful restart-enabled router.

       
      Step 4 end


      Example:
      Router(config)# end
       

      Exits to privileged EXEC mode.

       

      Setting a Hello Refresh Interval

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

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

        4.    end


      DETAILED STEPS
          Command or Action Purpose
        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 a hello refresh interval on a router with graceful restart enabled.

         
        Step 4 end


        Example:
        Router(config)# end
         

        Exits to privileged EXEC mode.

         

        Setting a Missed Refresh Limit

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

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

          4.    end


        DETAILED STEPS
            Command or Action Purpose
          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
           

          Sets a refresh limit on a router with graceful restart enabled.

           
          Step 4 end


          Example:
          Router(config)# end
           

          Exits to privileged EXEC mode.

           

          Verifying Graceful Restart Configuration

          SUMMARY STEPS

            1.    enable

            2.    show ip rsvp hello graceful-restart

            3.    end


          DETAILED STEPS
              Command or Action Purpose
            Step 1 enable


            Example:
            Router> enable
             

            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 graceful restart and related parameters.

             
            Step 3 end


            Example:
            Router# end
             

            Exits to user EXEC mode.

             

            Configuration Examples for MPLS TE—RSVP Graceful Restart

            MPLS TE—RSVP Graceful Restart Example

            In the following example, graceful restart is enabled, and related parameters, including a DSCP value, a refresh interval, and a missed refresh limit are set:

            Router# configure terminal
            Enter configuration commands, one per line.  End with CNTL/Z.
            Router(config)# ip rsvp signalling hello graceful-restart mode help-neighbor
            Router(config)# ip rsvp signalling hello graceful-restart dscp 30
            Router(config)# ip rsvp signalling hello graceful-restart refresh interval 10000
            Router(config)# ip rsvp signalling hello graceful-restart refresh misses 4
            Router(config)# end
            

            The following example verifies the status of graceful restart and the configured parameters:

            Router# show ip rsvp hello graceful-restart
            Graceful Restart:Enabled (help-neighbor only)
              Refresh interval:10000 msecs
              Refresh misses:4
              DSCP:0x30
              Advertised restart time:0 secs
              Advertised recovery time:0 secs
              Maximum wait for recovery:3600000 secs

            Additional References

            Related Documents

            Related Topic

            Document Title

            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

            QoS signalling

            Signalling Overview

            QoS congestion management

            Congestion Management Overview

            Stateful switchover

            Stateful Switchover

            MPLS Label Distribution Protocol

            MPLS Label Distribution Protocol (LDP)

            Information on stateful switchover, Cisco nonstop forwarding, graceful restart

            NSF/SSO—MPLS TE and RSVP Graceful Restart

            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 IOS 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 3478

            Graceful Restart Mechanism for Label Distribution

            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 MPLS Traffic Engineering—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 MPLS Traffic Engineering—RSVP Graceful Restart

            Feature Name

            Releases

            Feature Information

            MPLS Traffic Engineering—RSVP Graceful Restart

            12.0(29)S

            12.2(33)SRE

            12.4(20)T

            Cisco IOS XE Release 2.3

            The MPLS TE—RSVP Graceful Restart feature allows a neighboring Route Processor (RP) to recover from disruption in control plane service (specifically, the Label Distribution Protocol (LDP) component) without losing its MPLS forwarding state.

            In Cisco IOS Release 12.0(29)S, this feature was introduced.

            In Cisco IOS Release 12.4(20)T, this feature was integrated.

            The following commands were introduced or modified: ip rsvp signalling hello graceful-restart dscp, ip rsvp signalling hello graceful-restart mode help-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.

            In Cisco IOS Release 12.2(33)SRE, per node hellos allow interoperability with Cisco IOS Release 12.0S.

            Glossary

            autonomous system—A collection of networks that share the same routing protocol and that are under the same system administration.

            ASBR—Autonomous System Boundary Router. A router that connects and exchanges information between two or more autonomous systems.

            backup tunnel—An MPLS traffic engineering tunnel used to protect other (primary) tunnels’ traffic when a link or node failure occurs.

            DSCP—differentiated services code point. Six bits in the IP header, as defined by the IETF. These bits determine the class of service provided to the IP packet.

            Fast Reroute—A mechanism for protecting MPLS traffic engineering (TE) 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. 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 neighboring Route Processor restart after a node failure has occurred.

            headend—The router that originates and maintains a given LSP. This is the first router in the LSP’s path.

            IGP—Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP.

            instance—A mechanism that implements the 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.

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

            LDP—Label Distribution Protocol. The protocol that supports MPLS hop-by-hop forwarding by distributing bindings between labels and network prefixes. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).

            LSP—label switched path. A configured connection between two routers, in which MPLS is used to carry packets. A path created by the concatenation of one or more label switched hops, allowing a packet to be forwarded by swapping labels from an MPLS node to another MPLS node.

            merge point—The tail of the backup tunnel.

            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.

            PLR—point of local repair. The headend of the backup tunnel.

            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.

            RP—Route processor. Processor module in routers that contains the CPU, system software, and most of the memory components that are used in the router. Sometimes called a supervisory processor.

            state—Information that a router must maintain about each LSP. The information is used for rerouting tunnels.

            tailend—The router upon which an 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.

            topology—The physical arrangement of network nodes and media within an enterprise networking structure.

            tunnel—Secure communications path between two peers, such as two routers.