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 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.

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

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-interval command.

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.

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:

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

interface type number

Example:

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:

Device(config-if)# bfd interval 50 min_rx 50 multiplier 5

Enables BFD on the interface.

Step 5

end

Example:

Device(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.


Note

From Cisco IOS Release 15.2(4)S, IS-IS support for BFD requires the BFD session to be started for the adjacency to work when both neighbors advertise support for BFD. For the ISIS session to be established, BFD should either be configured under both protocol and interface (complete configuration) or not configured at all.

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:

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 isis area-tag

Example:

Device(config)# router isis tag1

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

Step 4

bfd all-interfaces

Example:

Device(config-router)# bfd all-interfaces

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

Step 5

exit

Example:

Device(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:

(Optional) Enters interface configuration mode.

Step 7

isis bfd [disable ]

Example:

Device(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:

Device(config-if)# end

Returns the router to privileged EXEC mode.

Step 9

show bfd neighbors [details ]

Example:

Device# 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 details command when it is entered on a line card.

Step 10

show clns interface

Example:

Device# 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:

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

interface type number

Example:

Device(config)# interface fastethernet 6/0

Enters interface configuration mode.

Step 4

isis bfd [disable ]

Example:

Device(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:

Device(config-if)# end

Returns the router to privileged EXEC mode.

Step 6

show bfd neighbors [details ]

Example:

Device# 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 details command when it is entered on a line card.

Step 7

show clns interface

Example:

Device# 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:


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

interface type number

Example:

Enters interface configuration mode.

Step 4

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

Example:


Device(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:


Device(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 6

show dampening interface

Example:


Device# show dampening interface

Displays a summary of dampened interfaces.

Step 7

show interface dampening

Example:


Device# 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:


Device> enable

Enables higher privilege levels, such as privileged EXEC mode.

Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-type interface-number

Example:

Configures an interface type and enters interface configuration mode.

Step 4

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

Example:


Device(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:


Device(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:


Device(config-if)# end

Returns to privileged EXEC mode.

Configuring an IS-IS Point-to-Point Adjacency over Broadcast Media

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.

Note

Having a multipoint interface instead of a point-to-point interface 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:


Device> enable

Enables higher privilege levels, such as privileged EXEC mode.

Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-type interface-number

Example:

Configures an interface type and enters interface configuration mode.

Step 4

isis network point-to-point

Example:


Device(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:


Device(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 ] route
  7. show isis spf-log
  8. show isis [process-tag ] topology

DETAILED STEPS

  Command or Action Purpose
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

isis display delimiter [return count | character count ]

Example:


Device(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:


Device(config)# exit

Returns to privileged EXEC mode.

Step 5

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

Example:


Device# show isis database detail

Displays the IS-IS link-state database.

Step 6

show isis [process-tag ] route

Example:


Device# show isis financetag route

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

Step 7

show isis spf-log

Example:


Device# 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:


Device# 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 details command 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 details command 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 details command must be run on the line cards. The show bfd neighbors details command 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

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

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.