Enhancing Security in an IS-IS Network

Last Updated: October 22, 2011

This module describes processes that you can follow to enhance network security when you use Intermediate System-to-Intermediate System (IS-IS) in your network. You can set passwords, prevent unauthorized routers from forming adjacencies with routers in your IS-IS network, and use the IS-IS HMAC-MD5 Authentication and Enhanced Clear Text Authentication feature.

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 Enhancing Security in an IS-IS Network

  • Before performing the tasks in this module, you should be familiar with the concepts described in the "Integrated IS-IS Routing Protocol Overview" and "Configuring a Basic IS-IS Network" modules.
  • It is assumed you already have IS-IS running on your network.

Information About Enhancing Security in an IS-IS Network

Importance of Preventing Unauthorized Information from Entering an IS-IS Network

It is recommended that you configure the security features described in this module in order to prevent unauthorized routing messages from being placed into the network routing domain. You can set an authentication password for each interface, as well as set an area password for each IS-IS area to prevent unauthorized routers from injecting false routing information into the link-state database, or you can configure a type of IS-IS authentication--either IS-IS HMAC-MD5 or enhanced clear text authentication.

The following sections describe configuration tasks for IS-IS authentication. Two types of authentication are supported: IS-IS HMAC-MD5 and clear text. The task you perform depends on whether you are introducing authentication or migrating from an existing authentication scheme.

Before you can configure authentication, you must make the following decisions:

  • Whether to configure authentication for the IS-IS instance and/or for individual IS-IS interfaces (both tasks are included in this section).
  • At what level(s) authentication is to be used.
  • What type of authentication (IS-IS HMAC-MD5 or clear text) is to be used.

IS-IS Authentication Functionality

New style IS-IS authentication (IS-IS HMAC-MD5 and clear text) provides a number of advantages over the old style password configuration commands that were described in the previous sections, "Setting an Authentication Password for each Interface" and "Setting a Password at Level 1".

  • Passwords are encrypted when the software configuration is displayed.
  • Passwords are easier to manage and change.
  • Passwords can be rolled over to new passwords without disrupting network operations.
  • Non-disruptive authentication transitions are supported by allowing configuration which allowed the router to accept PDUs without authentication or with stale authentication information, yet send PDUs with current authentication. Such transitions are useful when you are migrating from no authentication to some type of authentication, when you are changing authentication type, and when you are changing keys.

IS-IS has five PDU types: link state PDU (LSP), LAN Hello, Point-to-Point Hello, complete sequence number PDU (CSNP), and partial sequence number PDU (PSNP). IS-IS HMAC-MD5 authentication or clear text password authentication can be applied to all five PDU types. The authentication can be enabled on different IS-IS levels independently. The interface-related PDUs (LAN Hello, Point-to-Point Hello, CSNP, and PSNP) can be enabled with authentication on different interfaces, with different levels and different passwords.

Either authentication mode or old password mode may be configured on a given scope (IS-IS instance or interface) and level--bit not both. However, different modes may be configured for different modes mat be configured for different scopes or levels. If mixed modes are intended, different keys should be used for different modes in order not to compromise the encrypted password in the PDUs.

Benefits of IS-IS Clear Text Authentication

IS-IS clear text (plain text) authentication provides the same functionality as is provided by using the area-password or domain-password command. However, use of clear text authentication takes advantage of the more flexible key management capabilities described above.

Benefits of IS-IS HMAC-MD5 Authentication

  • IS-IS now supports MD5 authentication, which is more secure than clear text authentication. IS-IS HMAC-MD5 authentication adds an HMAC-MD5 digest to each IS-IS protocol data unit (PDU). HMAC is a mechanism for message authentication codes (MACs) using cryptographic hash functions. The digest allows authentication at the IS-IS routing protocol level, which prevents unauthorized routing messages from being injected into the network routing domain.
  • MD5 authentication or clear text authentication can be enabled on Level 1 or Level 2 independently.
  • Passwords can be rolled over to new passwords without disrupting routing messages.
  • For the purpose of network transition, you can configure the networking device to accept PDUs without authentication or with wrong authentication information, yet send PDUs with authentication. Such transition might be because you are migrating from no authentication to some type of authentication, you are changing authentication type, or you are changing keys.

Before you migrate from using one type of security authentication to another, all routers must be loaded with the new image that supports the new authentication type. The routers will continue to use the original authentication method until all routers have been loaded with the new image that supports the new authentication method, and all routers have been configured to use the new authentication method. Once all routers are loaded with the required image, you must follow the configuration steps for the desired new authentication method as described in the previous Configuring HMAC-MD5 or Clear Text Authentication for the IS-IS Instance. You also must decide whether to configure authentication for the IS-IS area or for individual IS-IS interfaces. Both tasks are included in the referenced section.


Note
To achieve a smooth transition from one authentication method to another, allowing for continuous authentication of IS-IS PDUs, perform the task steps in the order shown, which requires moving from router to router doing certain steps before all the steps are performed on any one router.
Migration from Old Clear Text Authentication to HMAC-MD5 Authentication

When you configure MD5 authentication, the area-password and domain-password command settings will be overridden automatically with the new authentication commands. When you configure MD5 authentication, the isis password command setting will be overridden automatically with the new authentication commands.

Migration from Old Clear Text Authentication to the New Clear Text Authentication

The benefits of migrating from the old method of clear text authentication to the new method of clear text authentication are as follows:

  • Passwords are easier to change and maintain.
  • Passwords can be encrypted when the system configuration is being displayed (if you use key management).

How to Enhance Security in an IS-IS Network

Setting an Authentication Password for each Interface


Note

The password is exchanged as plain text and thus provides only limited security.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    isis password password [level-1| level-2]

5.    Repeat Step 4 for each interface password that you want to set.

6.    end

7.    show ip interface [type number] [brief]


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 gigabitethernet 0/0/0

 

Enters interface configuration mode.

 
Step 4
isis password password [level-1| level-2]


Example:

Router(config-if)# isis password sjpass level-1

 

Configures the authentication password for an interface.

  • Different passwords can be assigned for different routing levels using the level-1 and level-2 keywords.
  • Specifying the level-1 or level-2 keyword disables the password only for Level 1 or Level 2 routing, respectively.
 
Step 5
Repeat Step 4 for each interface password that you want to set. 

--

 
Step 6
end


Example:

Router(config-if)# end

 

Returns to privileged EXEC mode.

 
Step 7
show ip interface [type number] [brief]


Example:

Router# show ip interface gigabitethernet 0/0/0

 

Displays the usability status of interfaces configured for IP.

 

Setting a Password at Level 1


Note

This password is exchanged as plain text, and, thus, this feature provides only limited security.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router isis [area- tag]

4.    area-password password

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
router isis [area- tag]


Example:

Router(config)# router isis salesarea

 

Enables IS-IS as an IP routing protocol and assigns a tag to a process, if required.

  • Enters router configuration mode.
 
Step 4
area-password password


Example:

Router(config-router)# area-password companyz

 

Configures the IS-IS area authentication password.

  • Using the area-password command on all routers in an area will prevent unauthorized routers from injecting false routing information into the link-state database.
  • This password is inserted in Level 1 protocol data unit (PDU) link-state PDUs (LSPs), complete sequence number PDUs (CSNPs), and partial sequence number PDUs (PSNPs).
 
Step 5
end


Example:

Router(config-router)# end

 

Returns to privileged EXEC mode.

 

Setting a Password at Level 2


Note

This password is exchanged as plain text, and, thus, this feature provides only limited security.
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    router isis [area-tag]

4.    domain-password password [authenticate snp {validate | send-only}]

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
router isis [area-tag]


Example:

Router(config)# router isis salesarea

 

Enables IS-IS as an IP routing protocol and assigns a tag to a process, if required.

  • Enters router configuration mode.
 
Step 4
domain-password password [authenticate snp {validate | send-only}]


Example:

Router(config-router)# domain-password company2

 

Configures the IS-IS routing domain authentication password.

Note    If you do not specify the authenticate snp keyword along with either the validate or send-only keyword, the IS-IS routing protocol does not insert the password into SNPs.
Note    Using the domain-password command on all routers in an area will prevent unauthorized routers from injecting false routing information into the link-state database.
Note    This password is inserted in Level 2 PDU link-state PDUs (LSPs), complete sequence number PDUs (CSNPs), and partial sequence number PDUs (PSNPs). If you specify the authenticate snp keyword along with either the validate or send-only keyword, the IS-IS routing protocol will insert the password into sequence number PDUs (SNPs).
 
Step 5
end


Example:

Router(config-router)# end

 

Returns to privileged EXEC mode.

 

Configuring IS-IS Authentication

Configuring HMAC-MD5 Authentication or Clear Text Authentication for the First Time

Configuring HMAC-MD5 or Clear Text Authentication for the IS-IS Instance
Before You Begin

In order to use HMAC-MD5 or clear text authentication with encrypted keys, the Integrated IS-IS routing protocol must be configured.


SUMMARY STEPS

1.    enable

2.    configure terminal

3.    key chain name-of-chain

4.    key key-id

5.    key-string text

6.    exit

7.    exit

8.    router isis [area- tag]

9.    authentication send-only [level-1 | level-2]

10.    Repeat Steps 1 through 9 on each router that will communicate.

11.    authentication mode {md5 | text}[level-1 | level-2]

12.    authentication key-chain name-of-chain [level-1 | level-2]

13.    Repeat Steps 11 and 12 on each router that will communicate.

14.    no authentication send-only

15.    Repeat Step 14 on each router that will communicate.


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
key chain name-of-chain


Example:

Router(config)# key chain remote3754

 

Enables authentication for routing protocols and identifies a group of authentication keys.

 
Step 4
key key-id


Example:

Router(config-keychain)# key 100

 

Identifies an authentication key on a key chain.

  • The key-id argument must be a number.
 
Step 5
key-string text


Example:

Router(config-keychain-key)# key-string mno172

 

Specifies the authentication string for a key.

  • The text argument can be 1 to 80 uppercase or lowercase alphanumeric characters; the first character cannot be a number.
 
Step 6
exit


Example:

Router(config-keychain-key)# exit

 

Returns to keychain configuration mode.

 
Step 7
exit


Example:

Router(config-keychain)# exit

 

Returns to global configuration mode.

 
Step 8
router isis [area- tag]


Example:

Router(config)# router isis 1

 

Enables IS-IS as an IP routing protocol and assigns a tag to a process, if required.

  • Enters router configuration mode.
 
Step 9
authentication send-only [level-1 | level-2]


Example:

Router(config-router)# authentication send-only

 

Specifies for the IS-IS instance that MD5 authentication is performed only on IS-IS PDUs being sent (not received).

 
Step 10
Repeat Steps 1 through 9 on each router that will communicate. 

Use the same key string on each router.

 
Step 11
authentication mode {md5 | text}[level-1 | level-2]


Example:

Router(config-router)# authentication mode md5

 

Specifies the type of authentication used in IS-IS PDUs for the IS-IS instance.

  • Specify md5 for MD5 authentication.
  • Specify text for clear text authentication.
 
Step 12
authentication key-chain name-of-chain [level-1 | level-2]


Example:

Router(config-router)# authentication key-chain remote3754

 

Enables MD5 authentication for the IS-IS instance.

 
Step 13
Repeat Steps 11 and 12 on each router that will communicate. 

--

 
Step 14
no authentication send-only


Example:

Router(config-router)# no authentication send-only

 

Specifies for the IS-IS instance that MD5 authentication is performed on IS-IS PDUs being sent and received.

  • In Step 9 you enable authentication to be performed only for IS-IS PDUs that are being sent. In Step 14 you enter the no authentication send-only command so that the authentication is now performed on PDUs sent and received.
 
Step 15
Repeat Step 14 on each router that will communicate. 

--

 
Configuring HMAC-MD5 or Clear Text Authentication for an IS-IS Interface
SUMMARY STEPS

1.    enable

2.    configure terminal

3.    key chain name-of-chain

4.    key key-id

5.    key-string text

6.    exit

7.    exit

8.    interface type number

9.    isis authentication send-only [level-1 | level-2]

10.    Repeat Steps 1 through 9 on each router that will communicate.

11.    isis authentication mode {md5 | text}[level-1 | level-2]

12.    isis authentication key-chain name-of-chain [level-1 | level-2]

13.    Repeat Steps 11 and 12 on each router that will communicate.

14.    no isis authentication send-only

15.    Repeat Step 14 on each router that will communicate.


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
key chain name-of-chain


Example:

Router(config)# key chain multistate87723

 

Enables authentication for routing protocols and identifies a group of authentication keys.

 
Step 4
key key-id


Example:

Router(config-keychain)# key 201

 

Identifies an authentication key on a key chain.

  • The key-id argument must be a number.
 
Step 5
key-string text


Example:

Router(config-keychain-key)# key-string idaho

 

Specifies the authentication string for a key.

  • The text argument can be 1 to 80 uppercase or lowercase alphanumeric characters; the first character cannot be a number.
 
Step 6
exit


Example:

Router(config-keychain-key)# exit

 

Returns to keychain configuration mode.

 
Step 7
exit


Example:

Router(config-keychain)# exit

 

Returns to global configuration mode.

 
Step 8
interface type number


Example:

Router(config)# interface gigabitethernet 0/0/0

 

Configures an interface.

 
Step 9
isis authentication send-only [level-1 | level-2]


Example:

Router(config-if)# isis authentication send-only

 

Specifies that authentication is performed only on PDUs being sent (not received) on a specified IS-IS interface.

 
Step 10
Repeat Steps 1 through 9 on each router that will communicate. 

Use the same key string on each router.

 
Step 11
isis authentication mode {md5 | text}[level-1 | level-2]


Example:

Router(config-if)# isis authentication mode md5

 

Specifies the type of authentication used for an IS-IS interface.

  • Specify md5 for MD5 authentication.
  • Specify text for clear text authentication.
 
Step 12
isis authentication key-chain name-of-chain [level-1 | level-2]


Example:

Router(config-if)# isis authentication key-chain multistate87723

 

Enables MD5 authentication for an IS-IS interface.

 
Step 13
Repeat Steps 11 and 12 on each router that will communicate. 

--

 
Step 14
no isis authentication send-only


Example:

Router(config-if)# no isis authentication send-only

 

Specifies that authentication is performed on PDUs being sent and received on a specified IS-IS interface.

 
Step 15
Repeat Step 14 on each router that will communicate. 

--

 

Migrating to a New Authentication Type

SUMMARY STEPS

1.    Load all routers with the image required to support the new, desired authentication method.

2.    Configure the new authentication mode on both the interface and the IS-IS area by following the appropriate tasks in the Configuring HMAC-MD5 Authentication or Clear Text Authentication for the First Time.


DETAILED STEPS
Step 1   Load all routers with the image required to support the new, desired authentication method.
Step 2   Configure the new authentication mode on both the interface and the IS-IS area by following the appropriate tasks in the Configuring HMAC-MD5 Authentication or Clear Text Authentication for the First Time.

Configuring Authentication on a New Router Being Added to a Network That Already Has Authentication Configured

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    key chain name-of-chain

4.    key key-id

5.    key-string text

6.    exit

7.    exit

8.    interface type number

9.    isis authentication mode {md5 | text}[level-1 | level-2]

10.    isis authentication key-chain name-of-chain [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
key chain name-of-chain


Example:

Router(config)# key chain multistate87723

 

Enables authentication for routing protocols and identifies a group of authentication keys.

 
Step 4
key key-id


Example:

Router(config-keychain)# key 201

 

Identifies an authentication key on a key chain.

  • The key-id argument must be a number.
 
Step 5
key-string text


Example:

Router(config-keychain-key)# key-string idaho

 

Specifies the authentication string for a key.

  • The text argument can be 1 to 80 uppercase or lowercase alphanumeric characters; the first character cannot be a number.
 
Step 6
exit


Example:

Router(config-keychain-key)# exit

 

Returns to keychain configuration mode.

 
Step 7
exit


Example:

Router(config-keychain)# exit

 

Returns to global configuration mode.

 
Step 8
interface type number


Example:

Router(config)# interface gigabitethernet 0/0/0

 

Configures an interface.

 
Step 9
isis authentication mode {md5 | text}[level-1 | level-2]


Example:

Router(config-if)# isis authentication mode md5

 

Specifies the type of authentication used for an IS-IS interface.

  • Specify md5 for MD5 authentication.
  • Specify text for clear text authentication.
 
Step 10
isis authentication key-chain name-of-chain [level-1 | level-2]


Example:

Router(config-if)# isis authentication key-chain multistate87723

 

Enables MD5 authentication for an IS-IS interface.

 

Configuration Examples for Enhancing Security in an IS-IS Network

Example Configuring IS-IS HMAC-MD5 Authentication

The following example configures a key chain and key for IS-IS HMAC-MD5 authentication for GigabitEthernet interface 3/0/0 (on Hello PDUs) and for the IS-IS instance (on LSP, CSNP, and PSNP PDUs).

!
key chain cisco
 key 100
 key-string tasman-drive
!
interface GigabitEthernet3/0/0
 ip address 10.1.1.1 255.255.255.252
 ip router isis real_secure_network
 isis authentication mode md5 level-1
 isis authentication key-chain cisco level-1
!
router isis real_secure_network
 net 49.0000.0101.0101.0101.00
 is-type level-1
 authentication mode md5 level-1
 authentication key-chain cisco level-1
!

Example Configuring IS-IS Clear Text Authentication

The following example configures a key chain and key for IS-IS clear text authentication for GigabitEthernet interface 3/0/0 (on Hello PDUs) and for the IS-IS instance (on LSP, CSNP, and PSNP PDUs).

!
key chain cisco
 key 100
 key-string tasman-drive
!
interface GigabitEthernet3/0/0
 ip address 10.1.1.1 255.255.255.252
 ip router isis real_secure_network
 isis authentication mode text level-1
 isis authentication key-chain cisco level-1
!
router isis real_secure_network
 net 49.0000.0101.0101.0101.00
 is-type level-1
 authentication mode text level-1
 authentication key-chain cisco level-1
!

Additional References

Related Documents

Related Topic

Document Title

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

"Integrated IS-IS Routing Protocol Overview" module.

Configuring a basic IS-IS network

"Configuring a Basic IS-IS Network" module.

Key chains and key management

"Configuring IP Routing Protocol-Independent Features" module.

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

Cisco IOS IP Routing: ISIS Command Reference

Cisco IOS master command list, all releases

Cisco IOS Master Command List, All Releases

Standards

Standard

Title

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

--

MIBs

MIB

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

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

RFCs

RFC

Title

RFC 1321

The MD5 Message-Digest Algorithm

RFC 2104

HMAC: Keyed-Hashing for Message Authentication

RFC 3567

IS-IS Cryptographic Authentication

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 Enhancing Security in an IS-IS Network

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 Enhancing Security in an IS-IS Network

Feature Name

Releases

Feature Information

IS-IS HMAC-MD5 Authentication and Enhanced Clear Text Authentication

Cisco IOS XE Release 2.1

The IS-IS HMAC-MD5 authentication feature adds an HMAC-MD5 digest to each Intermediate System-to-Intermediate System (IS-IS) protocol data unit (PDU). The digest allows authentication at the IS-IS routing protocol level, which prevents unauthorized routing messages from being injected into the network routing domain. IS-IS clear text (plain text) authentication is enhanced so that passwords are encrypted when the software configuration is displayed and passwords are easier to manage and change.

This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2011 Cisco Systems, Inc. All rights reserved.