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Customizing IS-IS for Your Network Design

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Table Of Contents

Customizing IS-IS for Your Network Design

Contents

Prerequisites for Customizing IS-IS for Your Network Design

Information About Customizing IS-IS for Your Network Design

Enhancing Your IS-IS Network Design at the Interface Level

Setting the IS-IS Link-State Metrics

Prioritizing Designated Intermediate Systems for IS-IS

Enhancing Your IS-IS Network Design at the Router Level

Limiting Level 1 and Level 2 Operations on the IS-IS Router

Summarizing Address Ranges in the IS-IS Routing Table

Generating an IS-IS Default Route

Configuring an IS-IS Default Metric

Configuration Examples for Customizing IS-IS for Your Network Design

Configuring a Global Default Metric for IPv4: Example

Where to Go Next

Additional References

Related Documents

RFCs

Technical Assistance

Feature Information for Customizing IS-IS for Your Network Design


Customizing IS-IS for Your Network Design

First Published: November 30, 2007
Last Updated: May 5, 2008

This module describes optional tasks that you can perform to customize Intermediate System-to-Intermediate System (IS-IS) for your network design. You can optimize network traffic flow by setting metrics, specifying an IS-IS system type, summarizing addresses, generating a default route, and configuring a global default metric.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all of the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for Customizing IS-IS for Your Network Design" section

Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images

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

Contents

•Prerequisites for Customizing IS-IS for Your Network Design

•Information About Customizing IS-IS for Your Network Design

•Configuration Examples for Customizing IS-IS for Your Network Design

•Where to Go Next

•Additional References

•Feature Information for Customizing IS-IS for Your Network Design

Prerequisites for Customizing IS-IS for Your Network Design

•Before performing the tasks in this module, you should be familiar with the concepts described in the "Integrated IS-IS Routing Protocol Overview" module.

•You should understand the concept of IP addressing. For more information on IP addressing, see the "Configuring IPv4 Addresses" chapter of the Cisco IOS IP Addressing Services Configuration Guide.

•You should know your network design and how you want traffic to flow through it before configuring IS-IS. Define areas, prepare an addressing plan for the routers (including defining the network entity titles [NETs]), and determine the interfaces that will run Integrated IS-IS.

•IS-IS must be enabled.

Information About Customizing IS-IS for Your Network Design

This section contain the following tasks:

•Enhancing Your IS-IS Network Design at the Interface Level (optional)

•Enhancing Your IS-IS Network Design at the Router Level (optional)

Enhancing Your IS-IS Network Design at the Interface Level

To customize IS-IS to enhance your network design at the interface level, perform the following tasks:

•Setting the IS-IS Link-State Metrics (optional)

•Prioritizing Designated Intermediate Systems for IS-IS (optional)

Setting the IS-IS Link-State Metrics

You can enhance network traffic flow by configuring IS-IS metric values for Level-1 or Level-2 routing, in order to prioritize traffic through certain paths. You can customize network traffic flow by changing the metric cost for a specified interface. All IS-IS links use the metric of 10 by default. The protocol does not automatically incorporate link attributes such as bandwidth or delay when metric values are assigned. The total cost to a destination is the sum of the costs on all outgoing interfaces along a particular path from the source to the destination. The least-cost paths are preferred.

If you want to configure a global default metric, see the "Configuring an IS-IS Default Metric" section. See the following procedure for configuring the metric values for a specific interface.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type name

4. isis metric default-metric [level-1 | level-2]

5. end

6. show isis [process-tag] database [level-1] [level-2] [l1] [l2] [detail] [lspid]

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 name

Example:

Router(config)# interface ethernet 0

Enters interface configuration mode.

Step 4 

isis metric default-metric [level-1 | level-2]

Example:

Router(config-if)# isis metric 15 level-1

Configures the metric for an interface.

Note We highly recommend that you configure the metrics on all interfaces. If you do not do so, all links will have the same cost and the cost to reach any node in the network will be logically equivalent to the number of hops.

Step 5 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 6 

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

Example:

Router# show isis database detail

(Optional) Displays the IS-IS link-state database.

•To display information about each LSP and the link-state database, enter the detail keyword.


Prioritizing Designated Intermediate Systems for IS-IS

On multi-access networks, IS-IS elects a router to act as a pseudo-node representing the multi-access circuit. The elected router is known as the designated intermediate system (DIS). The DIS issues pseudo-node LSPs listing all of the routers which are reachable on the network. Each router on the network advertises in its non-pseudonode LSPs reachability to the DIS. This reduces the amount of information that needs to be advertised. A DIS is elected for each level that is operating on the network, for example both Level 1 and Level 2. By default, all routers have the same priority for being elected DIS. The MAC address of each router's interface onto the network is used as the tiebreaker. When all routers have the same priority, the addition or removal of a router onto the network can result in a chance in the DIS. This churn can be prevented by assigning a higher priority to the router which you wish to act as the DIS. Priorities can be configured individually for Level 1 and Level 2. By default the priority is 64. You can configure the priority in the range from 0 to 127.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type name

4. isis priority number-value [level-1 | level-2]

5. end

6. show clns interface type number

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 name

Example:

Router(config)# interface ethernet 0/3

Enters interface configuration mode.

Step 4 

isis priority number-value [level-1 | level-2]

Example:

Router(config-if)# ip priority 2 level-1

Configures the priority used in designated router election.

Step 5 

end

Example:

Router(config-if)# end

Exits interface configuration mode and returns to privileged EXEC mode.

Step 6 

show clns interface type number

Example:

Router# show clns interface ethernet 0/3

(Optional) Displays CLNS-specific information about the the interfaces running IS-IS.

•The command output will display the DIS for both Level 1 and Level 2.


Enhancing Your IS-IS Network Design at the Router Level

The tasks in the following sections are configured from router configuration mode and are not interface-specific:

•Limiting Level 1 and Level 2 Operations on the IS-IS Router

•Summarizing Address Ranges in the IS-IS Routing Table

•Generating an IS-IS Default Route

•Configuring an IS-IS Default Metric

Limiting Level 1 and Level 2 Operations on the IS-IS Router

By default Cisco IOS software enables both Level 1 and Level 2 operations on IS-IS routers. To specify that a router is to operate only as an area router (Level 1) or only as a backbone router (Level 2), use the is-type command. Specifying routers to act as Level 1, Level 2, or Level 1 and 2 can streamline your network design.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis

4. is-type {level-1 | level-1-2 | level-2-only}

5. end

6. show isis [ipv6] [*] topology [level-1] [level-2]

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

Example:

Router(config)# router isis

Enables IS-IS as an IP routing protocol.

•Enters router configuration mode.

Step 4 

is-type [level-1 | level-1-2 | level-2-only]

Example:

Router(config-router)# is-type level-1

Configures the routing level for an instance of the IS-IS routing process.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show isis [ipv6] [*] topology [level-1] [level-2]

Example:

Router# show isis topology level-1

(Optional) Displays a list of all connected routers in all areas.

•To confirm paths to all Level 1 or Level 2 routers in the area or areas in which this router resides, enter the level-1 or level-2 keywords, respectively.


Example

The following example shows output from the show isis topology command for a router within a dual CLNS-IP network. In this example, because neither the level-1 nor level-2 optional keywords were entered, information is displayed for both Level 1 and Level 2 routers. 

Router# show isis topology


Tag L2BB:

IS-IS paths to level-2 routers


System Id       Metric  Next-Hop        Interface       SNPA


0000.0000.0005  --

0000.0000.0009  10      0000.0000.0009  Tu529           *Tunnel*        

0000.0000.0017  20      0000.0000.0009  Tu529           *Tunnel*        

0000.0000.0053  30      0000.0000.0009  Tu529           *Tunnel*        

0000.0000.0068  20      0000.0000.0009  Tu529           *Tunnel* 


Tag A3253-01:

IS-IS paths to level-1 routers


System Id       Metric  Next-Hop        Interface       SNPA

0000.0000.0003  10      0000.0000.0003  Et1             0000.0c03.6944 

0000.0000.0005  --

0000.0000.0053  10      0000.0000.0053  Et1             0060.3e58.ccdb

Summarizing Address Ranges in the IS-IS Routing Table

You can configure a summary address to represent summarized (aggregate) addresses within the IS-IS routing table. This process is called route summarization. Using a summary address can enhance scalability and network stability because it reduces the amount of information that needs to be advertised and reduces the frequency of updates required. For example, a single route flap may not cause the summary advertisement to flap. The disadvantage of using the summary addresses is that routing may be sub-optimal, for example, the path to a specific destination covered by the summary address may be longer than it would have been, had all the individual addresses been advertised. Summary addresses are most commonly used to summarize routes from one Level-one area into the Level-2 subdomain. One summary address can include multiple groups of addresses for a given level. Routes learned from other routing protocols can also be summarized. The metric used to advertise the summary is the smallest metric of all the more-specific routes.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis

4. summary-address address mask {level-1 | level-1-2 | level-2} [tag tag-number] [metric metric-value]

5. end

6. show isis database verbose

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

Example:

Router(config)# router isis

Enables IS-IS as an IP routing protocol.

•Enters router configuration mode.

Step 4 

summary-address address mask {level-1 | level-1-2 | level-2}[tag tag-number] [metric metric-value]

Example:

Router(config-router)# summary-address 10.1.0.0 255.255.0.0 level-2

Creates aggregate addresses for IS-IS.

Note Multiple groups of addresses can be summarized for a given level. Routes learned from other routing protocols can also be summarized. The metric used to advertise the summary is the smallest metric of all the more-specific routes. This command helps reduce the size of the routing table.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show isis database verbose

Example:

Router# show isis database verbose

(Optional) Displays detailed information about the IS-IS database.


Generating an IS-IS Default Route

Whenever you specifically configure redistribution of routes into an IS-IS routing domain, the Cisco IOS software does not, by default, redistribute the default route into the IS-IS routing domain. If you wish to advertise a default route you must use the default-information originate command. This command causes a default route to be advertised by the router. Advertisement of the default route can be made conditional by using a route map. You can use the route map to identify the level into which the default route is to be announced, whether a particular non-default prefix must be reachable, etc.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis

4. default-information originate [route-map map-name]

5. end

6. show ip route

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

Example:

Router(config)# router isis

Enables IS-IS as an IP routing protocol.

•Enters router configuration mode.

Step 4 

default-information originate [route-map map-name]

Example:

Router(config-router)# default-information originate

Generates a default route into an IS-IS routing domain.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show ip route

Example:

Router# show ip route

(Optional) Displays the current state of the routing table.


Configuring an IS-IS Default Metric

This task explains how to configure an IS-IS default metric for all interfaces on the router.

In Cisco IOS software, IS-IS has a default metric value of 10 for all active interfaces. If the interface is passive, the default value is zero. Rather than change the metric values for the active interfaces one by one, you can configure a different default metric value to be used by all interfaces. All interfaces that had the original IS-IS default metric 10 will be configured with the new default value. Besides offering the user the convenience of being able to globally configure the value for all IS-IS interfaces, the feature helps prevent errors that may occur when interfaces are individually configured to change the metric value. For example the user may remove configured metrics from an interface, thereby restoring the default metric value of 10—perhaps unintentionally making that interface a highly preferred one in the network. Such an occurrence on the wrong interface could mean the rerouting of traffic across the network on an undesirable path.

Restrictions

If you have already configured a metric for a specific interface by entering the isis metric command, the metric that has been configured for that specific interface will take precedence over any default set by the metric command.

SUMMARY STEPS

1. enable

2. configure terminal

3. router isis

4. metric default-value [level-1 | level-2]

5. end

6. show clns interface [type number]

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

Example:

Router(config)# router isis 1

Enables IS-IS as an IP routing protocol.

•Enters router configuration mode.

Step 4 

metric default-value [level-1 | level-2]

Example:

Router(config-router)# metric 25 level-2

Globally sets a new default metric value for all IS-IS interfaces.

•The value 25 shown in the example will apply only to Level 2 IS-IS interfaces. If you do not enter the level-1 or level-2 keyword, the metric will be applied to both Level 1 and Level 2 IS-IS interfaces.

Step 5 

end

Example:

Router(config-router)# end

Exits router configuration mode and returns to privileged EXEC mode.

Step 6 

show clns interface [type number]

Example:

Router# show clns interface

(Optional) Displays the CLNS-specific information about each interface.

•Enter this command if you want to verify the IS-IS global default metric that is set for the interface.

Configuration Examples for Customizing IS-IS for Your Network Design

This section provides the following configuration example:

•Configuring a Global Default Metric for IPv4: Example

Configuring a Global Default Metric for IPv4: Example

The following configuration example for an IS-IS routing process called area1 sets a global default metric of 111 for the IS-IS interfaces: 

interface Ethernet3/1

 ip address 172.16.10.2 255.255.0.0

 ip router isis area1

 no ip route-cache

 duplex half

!

interface Ethernet3/2

 ip address 192.168.242.2 255.255.255.0

 ip router isis area1

 no ip route-cache

 duplex half

router isis area1

 net 01.0000.0309.1234.00

 metric-style wide

 metric 111

In the following example, the show clns interface command confirms that the IS-IS IPv4 interface metric for both Level 1 and Level 2 interfaces is assigned the new default metric value 111: 

Router# show clns interface


Ethernet3/1 is up, line protocol is up

  Checksums enabled, MTU 1497, Encapsulation SAP

  ERPDUs enabled, min. interval 10 msec.

  CLNS fast switching enabled

  CLNS SSE switching disabled

  DEC compatibility mode OFF for this interface

  Next ESH/ISH in 39 seconds

  Routing Protocol: IS-IS

    Circuit Type: level-1-2

    Interface number 0x0, local circuit ID 0x1

    Level-1 Metric: 111, Priority: 64, Circuit ID: mekong.01

    Level-1 IPv6 Metric: 10

    Number of active level-1 adjacencies: 0

    Level-2 Metric: 111, Priority: 64, Circuit ID: mekong.01

    Level-2 IPv6 Metric: 10

    Number of active level-2 adjacencies: 0

    Next IS-IS LAN Level-1 Hello in 922 milliseconds

    Next IS-IS LAN Level-2 Hello in 1 seconds

Ethernet3/2 is up, line protocol is up

  Checksums enabled, MTU 1497, Encapsulation SAP

  ERPDUs enabled, min. interval 10 msec.

  CLNS fast switching enabled

  CLNS SSE switching disabled

  DEC compatibility mode OFF for this interface

  Next ESH/ISH in 20 seconds

  Routing Protocol: IS-IS

    Circuit Type: level-1-2

    Interface number 0x1, local circuit ID 0x2

    Level-1 Metric: 111, Priority: 64, Circuit ID: mekong.02

    Level-1 IPv6 Metric: 10

    Number of active level-1 adjacencies: 1

    Level-2 Metric: 111, Priority: 64, Circuit ID: mekong.02

    Level-2 IPv6 Metric: 10

    Number of active level-2 adjacencies: 1

    Next IS-IS LAN Level-1 Hello in 2 seconds

    Next IS-IS LAN Level-2 Hello in 1 seconds

In the following example, the isis metric command is entered so that it will assign a metric value of 10. The metric value that is set with the isis metric command for Ethernet interface 3/1 will take precedence over the metric value that was previously set with the metric command. 

interface Ethernet3/1

 ip address 172.30.10.2 255.255.0.0

 ip router isis area1

 no ip route-cache

 duplex half

 isis metric 10

!

interface Ethernet3/2

 ip address 192.168.224.2 255.255.255.0

 ip router isis area1

 no ip route-cache

 duplex half

router isis area1

 net 01.0000.0309.1234.00

 metric-style wide

 metric 111

When the show clns interface command is entered, the router output confirms that the interface has an assigned IS-IS IPv4 metric value of 10: 

Router# show clns interface


Ethernet3/1 is up, line protocol is up

  Checksums enabled, MTU 1497, Encapsulation SAP

  ERPDUs enabled, min. interval 10 msec.

  CLNS fast switching enabled

  CLNS SSE switching disabled

  DEC compatibility mode OFF for this interface

  Next ESH/ISH in 53 seconds

  Routing Protocol: IS-IS

    Circuit Type: level-1-2

    Interface number 0x0, local circuit ID 0x1

    Level-1 Metric: 10, Priority: 64, Circuit ID: mekong.01

    Level-1 IPv6 Metric: 10

    Number of active level-1 adjacencies: 0

    Level-2 Metric: 10, Priority: 64, Circuit ID: mekong.01

    Level-2 IPv6 Metric: 10

    Number of active level-2 adjacencies: 0

    Next IS-IS LAN Level-1 Hello in 4 seconds

    Next IS-IS LAN Level-2 Hello in 4 seconds

Ethernet3/2 is up, line protocol is up

  Checksums enabled, MTU 1497, Encapsulation SAP

  ERPDUs enabled, min. interval 10 msec.

  CLNS fast switching enabled

  CLNS SSE switching disabled

  DEC compatibility mode OFF for this interface

  Next ESH/ISH in 30 seconds

  Routing Protocol: IS-IS

    Circuit Type: level-1-2

    Interface number 0x1, local circuit ID 0x2

    Level-1 Metric: 111, Priority: 64, Circuit ID: mekong.02

    Level-1 IPv6 Metric: 10

    Number of active level-1 adjacencies: 1

    Level-2 Metric: 111, Priority: 64, Circuit ID: mekong.02

    Level-2 IPv6 Metric: 10

    Number of active level-2 adjacencies: 1

    Next IS-IS LAN Level-1 Hello in 2 seconds

    Next IS-IS LAN Level-2 Hello in 922 milliseconds

Where to Go Next

•To customize IS-IS for achieving fast convergence and scalability, see the "Overview of IS-IS Fast Convergence" module.

•To enhance IS-IS network security, see the "Enhancing Security in an IS-IS Network" module.

Additional References

The following sections provide references related to customizing IS-IS for your network design.

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 Protocols Command Reference

Roadmap of IS-IS features

"Integrated IS-IS Features Roadmap" module

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

"Integrated IS-IS Routing Protocol Overview" module

Configuring IPv6

"Implementing IPv6 Addressing and Basic Connectivity" chapter in the Cisco IOS IPv6 Configuration Guide

Configuring the IS-IS protocol for IPv6 networks

"Implementing IS-IS for IPv6" module in the Cisco IOS IPv6 Configuration Guide


RFCs

RFCs
Title

RFC 1195

Use of OSI IS-IS for Routing in TCP/IP and Dual Environments


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for Customizing IS-IS for Your Network Design

Table 1 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Release 12.2(1), 12.0(3)S, or a later release appear in the table.

For information on a feature in this technology that is not documented here, see the "Integrated IS-IS Features Roadmap" module.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for Customizing IS-IS for Your Network Design

Feature Name
Releases
Feature Information

Integrated IS-IS Global Default Metric

12.0(27)S
12.2(25)S
12.3(4)T

The Integrated IS-IS Global Default Metric feature allows you to change the global IS-IS default metric for interfaces so that you need not change the metric values for the interfaces one by one. All interfaces that had the original IS-IS default metric 10 will be configured with the new global default value.

The following section provides information about this feature:

•Configuring an IS-IS Default Metric

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