IP Routing: ISIS Configuration Guide, Cisco IOS Release 15M&T
Enhancing Security in an IS-IS Network
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Contents

Enhancing Security in an IS-IS Network

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 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 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.

Configuring IS-IS 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.

Migrating to a New Authentication Type

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.

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 ActionPurpose
    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 ethernet 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 serial 1
     

    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 ActionPurpose
      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, preventing 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 ActionPurpose
        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, preventing 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).

        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.

         
        Step 5 end


        Example:
        Router(config-router)# end
         

        Returns to privileged EXEC mode.

         

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

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

        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.

        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 ActionPurpose
          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

          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.

          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 ActionPurpose
            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 ethernet 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 Method

            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 ActionPurpose
                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 ethernet 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 Ethernet interface 3 (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 Ethernet3
 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 Ethernet interface 3 (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 Ethernet3
 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

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

                Cisco IOS IP Routing: ISIS Command Reference

                Key chains and key management

                • Cisco IOS IP Routing: Protocol-Independent Command Reference
                • "Configuring IP Routing Protocol-Independent Features" module

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

                "Integrated IS-IS Routing Protocol Overview" module

                Standards

                Standard

                Title

                None

                --

                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

                12.0(21)ST 12.0(22)S 12.2(11)S 12.2(13)T 12.2(14)S Cisco IOS XE 3.1.0 SG

                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.