Configuring IP Summary Address for RIPv2

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.

Information About IP Summary Address for RIPv2

RIP Route Summarization

Summarizing routes in RIP Version 2 improves scalability and efficiency in large networks. Summarizing IP addresses means that there is no entry for child routes (routes that are created for any combination of the individual IP addresses contained within a summary address) in the RIP routing table, reducing the size of the table and allowing the router to handle more routes.

Summary IP address functions more efficiently than multiple individually advertised IP routes for the following reasons:

  • The summarized routes in the RIP database are processed first.
  • Any associated child routes that are included in a summarized route are skipped as RIP looks through the routing database, reducing the processing time required.

Cisco routers can summarize routes in two ways:

  • Automatically, by summarizing subprefixes to the classful network boundary when crossing classful network boundaries (automatic summary).

Note

Automatic summary is enabled by default.

  • As specifically configured, advertising a summarized local IP address pool on the specified interface (on a network access server) so that the address pool can be provided to dialup clients.

When RIP determines that a summary address is required in the RIP database, a summary entry is created in the RIP routing database. As long as there are child routes for a summary address, the address remains in the routing database. When the last child route is removed, the summary entry also is removed from the database. This method of handling database entries reduces the number of entries in the database because each child route is not listed in an entry, and the aggregate entry itself is removed when there are no longer any valid child routes for it.

RIP Version 2 route summarization requires that the lowest metric of the "best route" of an aggregated entry, or the lowest metric of all current child routes, be advertised. The best metric for aggregated summarized routes is calculated at route initialization or when there are metric modifications of specific routes at advertisement time, and not at the time the aggregated routes are advertised.

The ip summary-address rip routerconfiguration command causes the router to summarize a given set of routes learned via RIP Version 2 or redistributed into RIP Version 2. Host routes are especially applicable for summarization.

You can verify which routes are summarized for an interface using the show ip protocols EXEC command. You can check summary address entries in the RIP database. These entries will appear in the database only if relevant child routes are being summarized. To display summary address entries in the RIP routing database entries if there are relevant routes being summarized based upon a summary address, use the show ip rip database command in EXEC mode. When the last child route for a summary address becomes invalid, the summary address is also removed from the routing table.

Authentication in RIP

The Cisco implementation of the Routing Information Protocol (RIP) Version 2 (RIPv2) supports authentication, key management, route summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).

By default, the software receives RIP Version 1 (RIPv1) and RIPv2 packets, but sends only RIPv1 packets. You can configure the software to receive and send only RIPv1 packets. Alternatively, you can configure the software to receive and send only RIPv2 packets. To override the default behavior, you can configure the RIP version that an interface sends. Similarly, you can also control how packets received from an interface are processed.

RIPv1 does not support authentication. If you are sending and receiving RIP v2 packets, you can enable RIP authentication on an interface.

The key chain determines the set of keys that can be used on the interface. Authentication, including default authentication, is performed on that interface only if a key chain is configured. For more information on key chains and their configuration, see the “Managing Authentication Keys” section in the “Configuring IP Routing Protocol-Independent Features” chapter in the Cisco IOS IP Routing: Protocol-Independent Configuration Guide.

Cisco supports two modes of authentication on an interface on which RIP is enabled: plain-text authentication and message digest algorithm 5 (MD5) authentication. Plain-text authentication is the default authentication in every RIPv2 packet.


Note

Do not use plain text authentication in RIP packets for security purposes, because the unencrypted authentication key is sent in every RIPv2 packet. Use plain-text authentication when security is not an issue; for example, you can use plain-text authentication to ensure that misconfigured hosts do not participate in routing.

Source IP Addresses of RIP Routing Updates

By default, the Cisco software validates the source IP address of incoming Routing Information Protocol (RIP) routing updates. If the source address is not valid, the software discards the routing update. You must disable this functionality if you want to receive updates from a device that is not part of this network. However, disabling this functionality is not recommended under normal circumstances.

How to Configure IP Summary Address for RIPv2

Summarizing RIP Routes

RIP Version 2 supports automatic route summarization by default. The software summarizes subprefixes to the classful network boundary when classful network boundaries are crossed.

If you have disconnected subnets, disable automatic route summarization to advertise the subnets. When route summarization is disabled, the software sends subnet and host routing information across classful network boundaries. To disable automatic summarization, use the no auto-summary command in router configuration mode.


Note

Supernet advertisement (advertising any network prefix less than its classful major network) is not allowed in RIP route summarization, other than advertising a supernet learned in the routing tables. Supernets learned on any interface that is subject to configuration are still learned.

For example, the following supernet summarization is invalid: 

Router(config)# interface gigabitEthernet 0/0/0
Router(config-if)# ip summary-address rip 10.0.0.0 252.0.0.0 
.
.
.

Each route summarization on an interface must have a unique major network, even if the subnet mask is unique. For example, the following configuration is not permitted: 

Router(config)# interface gigabitEthernet 0/0/0
 
Router(config)# ip summary-address rip 10.1.0.0 255.255.0.0
 
Router(config)# ip summary-address rip 10.2.2.0 255.255.255.0
 
.
.
.
SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    ip summary-address rip ip-address network-mask

    5.    exit

    6.    router rip

    7.    no auto-summary

    8.    end


DETAILED STEPS
      Command or Action Purpose
    Step 1 enable


    Example: 
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example: 
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 interface type number


    Example: 
    Router(config)# interface gigabitEthernet 0/0/0
     

    Enters the interface configuration mode.

     
    Step 4 ip summary-address rip ip-address network-mask


    Example: 
    Router(config-if)# ip summary-address rip 10.2.0.0 255.255.0.0
     

    Specifies the IP address and network mask that identify the routes to be summarized.

     
    Step 5 exit


    Example: 
    Router(config-if)# exit
     

    Exits the interface configuration mode.

     
    Step 6 router rip


    Example: 
    Router(config)# router rip
     

    Enters the router configuration mode.

     
    Step 7 no auto-summary


    Example: 
    Router(config-router)# no auto-summary
     

    Used in router configuration mode, disables automatic summarization.

     
    Step 8 end


    Example: 
    Router(config-router)# end
     

    Exits router configuration mode and returns to privileged EXEC mode.

     

    Specifying a RIP Version and Enabling Authentication

    Perform this task to specify a RIP version and enable authentication.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    router rip

      4.    version {1 | 2}

      5.    exit

      6.    interface type number

      7.    ip rip send version [1] [2]

      8.    ip rip receive version [1] [2]

      9.    ip rip authentication key-chain name-of-chain

      10.    ip rip authentication mode {text | md5}

      11.    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 rip


      Example: 
      Router(config)# router rip
       

      Enters router configuration mode.

       
      Step 4 version {1 | 2}


      Example: 
      Router(config-router)# version 1
       

      Configures an interface to send only RIP Version 1 packets.

       
      Step 5 exit


      Example: 
      Router(config-router)# exit
       

      Exits the router configuration mode and enters the global configuration mode.

       
      Step 6 interface type number


      Example: 
      Router(config)# interface gigabitEthernet 0/0/0
       

      Enters interface configuration mode.

       
      Step 7 ip rip send version [1] [2]


      Example: 
      Router(config-if)# ip rip send version 1
       

      Configures an interface to send only RIP Version 1 packets.

       
      Step 8 ip rip receive version [1] [2]


      Example: 
      Router(config-if)# ip rip receive version 1
       

      Configures an interface to accept only RIP Version 1 packets.

       
      Step 9 ip rip authentication key-chain name-of-chain


      Example: 
      Router(config-if)# ip rip authentication key-chain chainname
       

      Enables RIP authentication.

       
      Step 10 ip rip authentication mode {text | md5}


      Example: 
      Router(config-if)# ip rip authentication mode md5
       

      Configures the interface to use MD5 digest authentication (or let it default to plain text authentication).

       
      Step 11 end


      Example: 
      Router(config-if)# end
       

      Exits interface configuration mode and returns to privileged EXEC mode.

       

      Disabling the Validation of Source IP Addresses


      Note

      We recommend that you do not change the state of the default configuration unless you are certain that your application requires making a change in the configuration to advertise routes properly. Remember that if split horizon is disabled on a serial interface (and that interface is attached to a packet-switched network), you must disable split horizon for all devices in any relevant multicast groups on that network.

      The summarized network will not be advertised when split horizon is enabled.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    interface type number

        4.    ip split-horizon

        5.    exit

        6.    router rip

        7.    no validate-update-source

        8.    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: 
        Device(config)# interface serial 0/0/0
         

        Enters interface configuration mode.

         
        Step 4 ip split-horizon


        Example: 
        Device(config-if)# ip split-horizon
         

        Enables split horizon.

         
        Step 5 exit


        Example: 
        Device(config-if)# exit
         

        Exits interface configuration mode.

         
        Step 6 router rip


        Example: 
        Device(config)# router rip
         

        Enters router configuration mode.

         
        Step 7 no validate-update-source


        Example: 
        Device(config-router)# no validate-update-source
         

        Disables the validation of the source IP address of incoming Routing Information Protocol (RIP) routing updates.

         
        Step 8 end


        Example: 
        Device(config-router)# end
         

        Exits router configuration mode and returns to privileged EXEC mode.

         

        Configuring Examples for IP Summary Address for RIPv2

        Route Summarization Example

        The following example shows how the ip summary-address riprouter configuration command can be used to configure summarization on an interface. In this example, the subnets 10.1.3.0/25, 10.1.3.128/25, 10.2.1.0/24, 10.2.2.0/24, 10.1.2.0/24 and 10.1.1.0/24 can be summarized as shown below while sending the updates over an interface.

        Router(config)#interface GigabitEthernet 0/2
Router(config-if)#ip summary-address rip 10.1.0.0 255.255.0.0
Router(config-if)#ip summary-address rip 10.2.0.0 255.255.0.0
Router(config-if)#ip summary-address rip 10.3.0.0 255.255.0.0

        Additional References for RIP

        Related Documents

        Related Topic

        Document Title

        Cisco IOS Commands

        Cisco IOS Master Command List, All Releases

        IP Routing: RIP commands

        Cisco IOS IP Routing: RIP Command Reference

        Standards and RFCs

        Standards/RFC

        Title

        RFC 1058

        Routing Information Protocol

        RFC 2453

        RIP Version 2

        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 he Cisco Support and Documentation we site requires a Cisco.com user ID and password.

        http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

        Feature Information for IP Summary Address for RIPv2

        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 IP Summary Address for RIPv2

        Feature Name

        Releases

        Feature Information

        IP Summary Address for RIPv2

        12.0(7)T

        12.1(3)T

        12.1(14)

        12.2(2)T

        12.2(27)SBB

        12.2(33)SRE

        15.0(1)M

        15.0S

        The IP Summary Adddress for RIPv2 feature introduced the ability to summarize routes. Summarizing routes in RIP Version 2 improves scalability and efficiency in large networks. Summarizing IP addresses means that there is no entry for child routes (routes that are created for any combination of the individual IP addresses contained within a summary address) in the RIP routing table, reducing the size of the table and allowing the router to handle more routes.

        The following commands were introduced or modified:

        ip summary-address rip.