Reducing Failure Detection Times in IS-IS Networks

This module describes how to customize IS-IS configuration to help you achieve fast convergence in your network. This module describes how to configure Bidirectional Failure Detection (BFD) as well as other tasks to optimize how a router that runs IS-IS detects link failures and topology changes, sends important topology change updates to its neighbors, and reacts to the topology change updates that it receives from its neighbors, in order to increase network performance.

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 Reducing Failure Detection Times in IS-IS Networks

You should be familiar with the concepts described in the "Overview of IS-IS Fast Convergence" module.

Information About Reducing Failure Detection Times in IS-IS Networks

BFD is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable.

For complete information about the BFD feature, see the following documentation:

"Bidirectional Forwarding Detection"

You can enable BFD support for routing protocols at the router level to enable BFD support globally for all interfaces or you can configure BFD on a per-interface basis at the interface level.

For Cisco IOS Release 12.4(4)T, and later releases, you must configure BFD support for one or more of the following routing protocols: BGP, IS-IS, and OSPF.

This section describes the procedures for configuring BFD support for IS-IS, so that IS-IS is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD. There are two methods for enabling BFD support for IS-IS:

  • You can enable BFD for all of the interfaces for which IS-IS is routing by using the bfd all-interfaces command in router configuration mode. You can then disable BFD for one or more of those interfaces using the isis bfd disable command in interface configuration mode.
  • You can enable BFD for a subset of the interfaces for which IS-IS is routing by using the isis bfd command in interface configuration mode.

IP event dampening introduces a configurable exponential delay mechanism to suppress the effects of excessive interface flapping events on routing protocols and routing tables in the network. This feature allows the network operator to configure a router to automatically identify and selectively dampen a local interface that is flapping, removing it from the network until it becomes stable again. Thus, the network becomes more stable, with a faster convergence time.

Tuning hello parameters should be considered only when the link type does not offer fast enough link failure detection. The standard default values for the hello interval and hello multiplier are 10 seconds and 3 seconds. Therefore, the multiplier times the interval will give a default hold-time of 30 seconds.

Although a slower hello interval saves bandwidth and CPU usage, there are some situations when a faster hello interval is preferred. In the case of a large configuration that uses Traffic Engineering (TE) tunnels, if the TE tunnel uses ISIS as the Interior Gateway Protocol (IGP), and the IP routing process is restarted at the router at the ingress point of the network (headend), then all the TE tunnels get resignaled with the default hello interval. A faster hello interval prevents this resignaling. To configure a faster hello interval, you need to decrease the ISIS hello interval manually using the isis hello-intervalcommand.

Configuring a point-to-point adjacency over a broadcast media can improve convergence times of a customer’s network because it prevents the system from electing a designated router (DR), prevents flooding from using CSNPs for database synchronization, and simplifies shortest path first (SPF) computations.

Importance of Fast Network Failure Detection

You can customize your IS-IS network to reduce the amount of time it takes for network failures to be discovered. When failures are detected more quickly, networks can react to them sooner and alternate paths can be selected more quickly, speeding up network convergence.

How to Reduce Failure Detection Times in IS-IS Networks

Using Bidirectional Forwarding Failure Detection to Decrease Failure Detection Times

Configuring BFD Session Parameters on the Interface

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

    5.    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 interface type number


    Example: 
    Router(config)# interface FastEthernet 6/0
     

    Enters interface configuration mode.

    • Repeat this procedure for each interface over which you want to run BFD sessions to BFD neighbors.
     
    Step 4 bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier


    Example: 
    Router(config-if)# bfd interval 50 min_rx 50 multiplier 5
     

    Enables BFD on the interface.

     
    Step 5 end


    Example: 
    Router(config-if)# end
     

    Exits interface configuration mode.

     

    Configuring BFD Support for IS-IS

    Prerequisites

    IS-IS must be running on all participating routers.

    The baseline parameters for BFD sessions on the interfaces that you want to run BFD sessions to BFD neighbors over must be configured. See the Configuring BFD Session Parameters on the Interface for more information.

    Configuring BFD Support for IS-IS for All Interfaces
    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    router isis area-tag

      4.    bfd all-interfaces

      5.    exit

      6.    interface type number

      7.    isis bfd [disable]

      8.    end

      9.    show bfd neighbors [details]

      10.    show clns interface


    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 router isis area-tag


      Example: 
      Router(config)# router isis tag1
       

      Specifies an IS-IS process and enters router configuration mode.

       
      Step 4 bfd all-interfaces


      Example: 
      Router(config-router)# bfd all-interfaces
       

      Enables BFD globally on all interfaces associated with the IS-IS routing process.

       
      Step 5 exit


      Example: 
      Router(config-router)# exit
       

      (Optional) Returns the router to global configuration mode. Enter this command only if you want to follow Step 6 and Step 7 to disable BFD for one or more interfaces.

       
      Step 6 interface type number


      Example: 
      Router(config)# interface fastethernet 6/0
       

      (Optional) Enters interface configuration mode.

       
      Step 7 isis bfd [disable]


      Example: 
      Router(config-if)# isis bfd
       

      Enables or disables BFD on a per-interface basis for one or more interfaces associated with the IS-IS routing process.

      Note   

      You should use the disable keyword only if you enabled BFD on all of the interfaces that IS-IS is associated with using the bfd all-interfaces command in router configuration mode.
       
      Step 8 end


      Example: 
      Router(config-if)# end
       

      Returns the router to privileged EXEC mode.

       
      Step 9 show bfd neighbors [details]


      Example: 
      Router# show bfd neighbors details
       

      Displays information that can be used to verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

      Note   

      In order to display the full output of the show bfd neighbors details command on a Cisco 12000 series router, you must enter the command on the line card. Enter the attach slot-number command to establish a CLI session with a line card. The registered protocols are not shown in the output of the show bfd neighbors detailscommandwhen it is entered on a line card.
       
      Step 10 show clns interface


      Example: 
      Router# show clns interface
       

      Displays information that can be used to verify if BFD for IS-IS has been enabled for a specific IS-IS interface that is associated.

       
      Configuring BFD Support for IS-IS for One or More Interfaces
      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface type number

        4.    isis bfd [disable]

        5.    end

        6.    show bfd neighbors [details]

        7.    show clns interface


      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 interface type number


        Example: 
        Router(config)# interface fastethernet 6/0
         

        Enters interface configuration mode.

         
        Step 4 isis bfd [disable]


        Example: 
        Router(config-if)# isis bfd
         

        Enables or disables BFD on a per-interface basis for one or more interfaces associated with the IS-IS routing process.

        Note   

        You should use the disable keyword only if you enabled BFD on all of the interfaces that IS-IS is associated with using the bfd all-interfaces command in router configuration mode.
         
        Step 5 end


        Example: 
        Router(config-if)# end
         

        Returns the router to privileged EXEC mode.

         
        Step 6 show bfd neighbors [details]


        Example: 
        Router# show bfd neighbors details
         

        Displays information that can help verify if the BFD neighbor is active and displays the routing protocols that BFD has registered.

        Note   

        In order to display the full output of the show bfd neighbors details command on a Cisco 12000 series router, you must enter the command on the line card. Enter the attach slot-number command to establish a CLI session with a line card. The registered protocols are not shown in the output of the show bfd neighbors detailscommandwhen it is entered on a line card.
         
        Step 7 show clns interface


        Example: 
        Router# show clns interface
         

        Displays information that can help verify if BFD for IS-IS has been enabled for a specific IS-IS interface that is associated.

         

        Using IP Event Dampening to Decrease Failure Detection Times

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    interface type number

          4.    dampening [half-life-period reuse-threshold] [suppress-threshold max-suppress-time [restart-penalty]]

          5.    end

          6.    show dampening interface

          7.    show interface dampening


        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 interface type number


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

          Enters interface configuration mode.

           
          Step 4 dampening [half-life-period reuse-threshold] [suppress-threshold max-suppress-time [restart-penalty]]


          Example: 
          Router(config-if)# dampening
           

          Enables interface dampening.

          • Entering the dampening command without any keywords or arguments enables interface dampening with the default configuration parameters.
          Note   

          The default values for the half-life-period, reuse-threshold, suppress-threshold, max-suppress-time, and restart-penalty arguments are 5, 1000, 2000, 20, and 2000, respectively.
          • When the timer for the restart-penalty argument is manually configured, the values must be manually entered for all arguments.
           
          Step 5 end


          Example: 
          Router(config-if)# end
           

          Exits interface configuration mode and returns to privileged EXEC mode.

           
          Step 6 show dampening interface


          Example: 
          Router# show dampening interface
           

          Displays a summary of dampened interfaces.

           
          Step 7 show interface dampening


          Example: 
          Router# show interface dampening
           

          Displays dampened interfaces on the local router.

           

          Tuning IS-IS Hello Parameters to Decrease Link Failure Detection Times

          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    interface interface-type interface-number

            4.    isis hello-interval {seconds | minimal} [level-1 | level-2]

            5.    isis hello-multiplier multiplier [level-1 | level-2]

            6.    end


          DETAILED STEPS
              Command or Action Purpose
            Step 1 enable


            Example: 
            Router> enable
             

            Enables higher privilege levels, such as privileged EXEC mode.

            Enter your password if prompted.

             
            Step 2 configure terminal


            Example: 
            Router# configure terminal
             

            Enters global configuration mode.

             
            Step 3 interface interface-type interface-number


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

            Configures an interface type and enters interface configuration mode.

             
            Step 4 isis hello-interval {seconds | minimal} [level-1 | level-2]


            Example: 
            Router(config-if)# isis hello-interval 5 level-1
             

            Specifies the length of time between the sending of IS-IS hello PDUs.

            • The default value is 10. The hello interval multiplied by the hello multiplier equals the hold time. If the minimal keyword is specified, the hold time is 1 second and the system computes the hello interval based on the hello multiplier.
            • The hello interval can be configured independently for Level 1 and Level 2, except on serial point-to-point interfaces. (Because only a single type of hello PDU is sent on serial links, it is independent of Level 1 or Level 2.) The level-1 and level-2 keywords are used on X.25, SMDS, and Frame Relay multiaccess networks or LAN interfaces.
            Note   

            A faster hello interval gives faster convergence, but increases bandwidth and CPU usage. It might also add to instability in the network, due to false failure detection events. A slower hello interval saves bandwidth and CPU. Especially when used in combination with a higher hello multiplier, this configuration may increase overall network stability, but has typical slower network convergence as a consequence.

             
            Step 5 isis hello-multiplier multiplier [level-1 | level-2]


            Example: 
            Router(config-if)# isis hello-multiplier 6 level-1
             

            Specifies the number of IS-IS hello PDUs a neighbor must miss before the router should declare the adjacency as down.

            • The default value is 3. A multiplier value of 1 is very aggressive--we recommend a value of at least 3.
             
            Step 6 end


            Example: 
            Router(config-if)# end
             

            Returns to privileged EXEC mode.

             

            Configuring an IS-IS Point-to-Point Adjacency over Broadcast Media to Reduce Link Failure Detection Times


            Note

            Perform this task for IS-IS networks that consist of only two networking devices connected to broadcast media. Such networks are usually configured as a point-to-point link rather than a broadcast link. In this case, it is recommended to follow this task to decrease the link failure detection time.

            Having a multipoint interface instead of the point-to-point interfaces will cause the creation of a pseudonode on the network. The addition of the pseudonode means that the router must retain information about it. To decrease the size of the topology database of the router, thereby reducing the memory requirement of the router and increasing the efficiency of the SPF calculation since there is one less node involved, configure point-to-point interfaces when possible.

            >
            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    interface interface-type interface-number

              4.    isis network point-to-point

              5.    end


            DETAILED STEPS
                Command or Action Purpose
              Step 1 enable


              Example: 
              Router> enable
               

              Enables higher privilege levels, such as privileged EXEC mode.

              Enter your password if prompted.

               
              Step 2 configure terminal


              Example: 
              Router# configure terminal
               

              Enters global configuration mode.

               
              Step 3 interface interface-type interface-number


              Example: 
              Router(config)# interface Fastethernet 4/0
               

              Configures an interface type and enters interface configuration mode.

               
              Step 4 isis network point-to-point


              Example: 
              Router(config-if)# isis network point-to-point
               

              Configures a network of only two networking devices that use broadcast media and the integrated IS-IS routing protocol to function as a point-to-point link instead of a broadcast link.

               
              Step 5 end


              Example: 
              Router(config-if)# end
               

              Returns to privileged EXEC mode.

               

              Monitoring IS-IS Network Convergence Time

              SUMMARY STEPS

                1.    enable

                2.    configure terminal

                3.    isis display delimiter [return count | character count]

                4.    exit

                5.    show isis database [level-1] [level-2] [l1] [l2] [detail] [lspid]

                6.    show isis [process-tag] routes

                7.    show isis spf-log

                8.    show isis [process-tag] topology


              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 isis display delimiter [return count | character count]


                Example: 
                Router(config)# isis display delimiter return 2
                 

                Makes output from multiarea displays easier to read by specifying the delimiter to use to separate displays of information.

                 
                Step 4 exit


                Example: 
                Router(config)# exit
                 

                Returns to privileged EXEC mode.

                 
                Step 5 show isis database [level-1] [level-2] [l1] [l2] [detail] [lspid]


                Example: 
                Router# show isis database detail
                 

                Displays the IS-IS link-state database.

                 
                Step 6 show isis [process-tag] routes


                Example: 
                Router# show isis financetag routes
                 

                Displays the IS-IS Level 1 forwarding table for IS-IS learned routes.

                 
                Step 7 show isis spf-log


                Example: 
                Router# show isis spf-log
                 

                Displays how often and why the router has run a full SPF calculation.

                 
                Step 8 show isis [process-tag] topology


                Example: 
                Router# show isis financetag topology
                 

                Displays a list of all connected routers in all areas.

                • If a process tag is specified, output is limited to the specified routing process. When "null" is specified for the process tag, output is displayed only for the router process that has no tag specified. If a process tag is not specified, output is displayed for all processes.
                 

                Configuration Examples for Reducing Failure Detection Times in IS-IS Networks

                Example Configuring BFD in an IS-IS Network

                In the following example, the simple IS-IS network consists of Router A and Router B. Fast Ethernet interface 0/1 on Router A is connected to the same network as Fast Ethernet interface 6/0 for Router B. The example, starting in global configuration mode, shows the configuration of BFD.

                Configuration for Router A

                !
interface FastEthernet 0/1
 ip address 172.16.10.1 255.255.255.0
ip router isis 
 bfd interval 50 min_rx 50 multiplier 3
!
interface FastEthernet 3/0.1
ip address 172.17.0.1 255.255.255.0
ip router isis 
!
router isis 
 net 49.0001.1720.1600.1001.00
 bfd all-interfaces
!

                Configuration for Router B

                !
interface FastEthernet 6/0
 ip address 172.16.10.2 255.255.255.0
ip router isis 
 bfd interval 50 min_rx 50 multiplier 3
!
interface FastEthernet 6/1
 ip address 172.18.0.1 255.255.255.0
ip router isis 
!
router isis 
 net 49.0000.0000.0002.00
 bfd all-interfaces
!

                The output from the show bfd neighbors detailscommand from Router A verifies that a BFD session has been created and that IS-IS is registered for BFD support:

                Router A
RouterA# show bfd neighbors details
 
OurAddr       NeighAddr     LD/RD RH  Holdown(mult)  State     Int
172.16.10.1   172.16.10.2    1/8  1   536  (3 )      Up        Fa0/1          
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 200000, MinRxInt: 200000, Multiplier: 5
Received MinRxInt: 1000, Received Multiplier: 3
Holdown (hits): 600(0), Hello (hits): 200(23543)
Rx Count: 13877, Rx Interval (ms) min/max/avg: 200/448/335 last: 64 ms ago
Tx Count: 23546, Tx Interval (ms) min/max/avg: 152/248/196 last: 32 ms ago
Registered protocols: ISIS 
Uptime: 01:17:09
Last packet: Version: 0            - Diagnostic: 0
             I Hear You bit: 1     - Demand bit: 0
             Poll bit: 0           - Final bit: 0
             Multiplier: 3         - Length: 24
             My Discr.: 8          - Your Discr.: 1
             Min tx interval: 50000    - Min rx interval: 1000
             Min Echo interval: 0

                The output from the show bfd neighbors detailscommand from the line card on Router B verifies that a BFD session has been created:


                Note

                Router B is a Cisco 12000 series router. The show bfd neighbors detailscommand must be run on the line cards. The show bfd neighbors detailscommand will not display the registered protocols when it is entered on a line card.

                		 
                Router B
RouterB# attach 6 
Entering Console for 8 Port Fast Ethernet in Slot: 6
Type "exit" to end this session
Press RETURN to get started!
LC-Slot6> show bfd neighbors details
Cleanup timer hits: 0
OurAddr       NeighAddr     LD/RD RH  Holdown(mult)  State     Int
172.16.10.2   172.16.10.1    8/1  1   1000 (5 )      Up        Fa6/0          
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 50000, MinRxInt: 1000, Multiplier: 3
Received MinRxInt: 200000, Received Multiplier: 5
Holdown (hits): 1000(0), Hello (hits): 200(5995)
Rx Count: 10126, Rx Interval (ms) min/max/avg: 152/248/196 last: 0 ms ago
Tx Count: 5998, Tx Interval (ms) min/max/avg: 204/440/332 last: 12 ms ago
Last packet: Version: 0            - Diagnostic: 0
             I Hear You bit: 1     - Demand bit: 0
             Poll bit: 0           - Final bit: 0
             Multiplier: 5         - Length: 24
             My Discr.: 1          - Your Discr.: 8
             Min tx interval: 200000    - Min rx interval: 200000
             Min Echo interval: 0
Uptime: 00:33:13
SSO Cleanup Timer called: 0
SSO Cleanup Action Taken: 0
Pseudo pre-emptive process count: 239103 min/max/avg: 8/16/8 last: 0 ms ago
 IPC Tx Failure Count: 0
 IPC Rx Failure Count: 0
 Total Adjs Found: 1

                Example Configuring IS-IS to Achieve Fast Convergence by Reducing Failure Detection Times

                The following example configures Ethernet interface 0/0 to use IP event dampening, setting the half life to 30 seconds, the reuse threshold to 1500, the suppress threshold to 10,000, and the maximum suppress time to 120 seconds. The IS-IS hello parameters have also been tuned for more rapid failure detection

                enable
configure terminal
interface Ethernet 0/0
 dampening 30 1500 10000 120
 isis hello-interval minimal
 isis hello-multiplier 3

                Where to Go Next

                To configure additional features to improve IS-IS network convergence times, complete the optional tasks in one or more of the following modules:

                • "Setting Best Practice Parameters for IS-IS Fast Convergence"
                • "Reducing Link Failure and Topology Change Notification Times in IS-IS Networks"
                • "Reducing Alternate-Path Calculation Times in IS-IS Networks"

                Additional References

                Related Documents

                Related Topic

                Document Title

                IS-IS commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples

                Cisco IOS IP Routing: ISIS Command Reference

                Overview of Cisco IS-IS conceptual information with links to all the individual IS-IS modules

                "Integrated IS-IS Routing Protocol Overview"

                Standards

                Standard

                Title

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

                --

                RFCs

                RFC

                Title

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

                --

                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 Reducing Failure Detection Times in IS-IS Networks

                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 Reducing Failure Detection Times in IS-IS Networks

                Feature Name

                Software Releases

                Feature Information

                IS-IS Support for BFD over IPv4

                Cisco IOS XE 3.2SE

                Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable.

                Integrated IS-IS Point-to-Point Adjacency over Broadcast Media

                12.2(8)T

                Cisco IOS XE 3.1.0 SG

                Cisco IOS XE 3.2SE

                When a network consists of only two networking devices connected to broadcast media and uses the integrated IS-IS protocol, it is better for the system to handle the link as a point-to-point link instead of as a broadcast link. This feature introduces a new command to make IS-IS behave as a point-to-point link between the networking devices.