Implementing Multicast Stub Routing

This module describes the concepts and configuration tasks used to implement multicast stub routing. Multicast stub routing can be used for the following purposes:

  • To prevent multicast transit when it is enforced by unicast stub routing.
  • To eliminate periodic flooding and pruning of dense mode traffic on low bandwidth links.
  • To reduce overall processing of Protocol Indendent Multicast (PIM) control traffic; and protect against multicast spoofing of PIM Designated Router (DR) messages and PIM assert messages.

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 Multicast Stub Routing

IP multicast is enabled and the Protocol Independent Multicast (PIM) interfaces are configured using the tasks described in the "Configuring Basic IP Multicast" module of the IP Multicast: PIM Configuration Guide.

Restrictions for Multicast Stub Routing

  • Multicast stub routing does not prevent the configuration of other Interior Gateway Protocols (IGPs) that do not support stub routing, such as Routing Information Protocol (RIP), Open Shortest Path First (OSPF), and Intermediate System-to-Intermediate System (IS-IS) to bypass this restriction. Multicast stub routing also does not prevent the configuration of static routing to bypass this restriction. Multicast stub routing is enforced by unicast stub routing. The proper unicast Enhanced Interior Gateway Routing Protocol (EIGRP) stub routing configuration will assist in multicast stub routing.

    Note

    For more information about unicast EIGRP stub routing, see the “Configuring EIGRP” module of the IP Routing: EIGRP Configuration Guide.

  • Multicast stub routing can only be implemented in nonredundant stub network topologies.

Information About Multicast Stub Routing

Multicast Stub Networks

Multicast stub networks are those segments that receivers are directly connected to for any multicast group, even though there are receivers interested in multicast traffic beyond those segments. Multicast stub routing can only be implemented in nonredundant stub network topologies.

Multicast Stub Routing Between Stub and Distribution Devices

Implementing multicast stub routing between the stub and distribution device is useful in PIM dense mode (PIM-DM) where periodic flooding and subsequent pruning of multicast traffic occurs for unwanted multicast groups. Multicast stub routing in this scenario prevents periodic flooding and pruning and also allows multicast traffic to be forwarded for groups in which receivers are available on the stub network.

Implementing multicast stub routing between the stub and distribution device in PIM sparse mode (PIM-SM) and bidirectional PIM (bidir-PIM) environments eliminates the need to maintain the group-to-Rendezvous Point (RP) mapping cache on the stub device, and saves periodic update bandwidth--if Auto-RP or PIM bootstrap router (BSR) is used for distributing the RP information.

Multicast stub routing is intended to forward multicast traffic from the distribution to the stub device. Although it is possible to have sources directly connected to the stub network, it would only work in a PIM-DM environment. It is not possible in PIM-SM, Source Specific Multicast (SSM), and bidirectional PIM (bidir-PIM) environments because the first hop device will be filtered by the PIM neighbor filter applied on the distribution device, resulting in reverse path forwarding (RPF) failures. Furthermore, receivers must be directly connected to the stub device and cannot be further downstream.

Multicast Stub Routing Between the Stub Device and Interested Receivers

Implementing multicast stub routing between the stub device and interested receivers is used to reduce the overall processing of PIM control traffic, especially as the number of stub links increases on the stub device, and to protect against DoS attacks targeted at the PIM DR.

Benefits of Multicast Stub Routing

Multicast stub routing allows such stub networks to be configured easily for multicast connectivity and provides the following benefits:

  • Prevents stub networks from being used for multicast transit when they are enforced by unicast stub routing (EIGRP).
  • Eliminates periodic flooding and pruning of dense mode traffic on low bandwidth links.
  • Reduces overall processing of PIM control traffic.
  • Protects against multicast spoofing of PIM DR messages and PIM assert messages.

Note

Multicast stub routing can only be implemented in nonredundant stub network topologies.

How to Implement Multicast Stub Routing

Configuring the Stub Device for Multicast Stub Routing

Perform this task to configure a stub device for multicast stub routing.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    Do one of the following:

    • ip pim passive
    • ip pim neighbor-filter access-list

    5.    ip igmp helper-address ip-address

    6.    end

    7.    show ip pim interface [type number]


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 GigabitEthernet0/0
     

    Enters interface configuration mode.

     
    Step 4 Do one of the following:
    • ip pim passive
    • ip pim neighbor-filter access-list


    Example: 
    Device(config-if)# ip pim passive


    Example: 
    Device(config-if)# ip pim neighbor-filter 1
     
    • The first sample shows how to configure the interface to operate in PIM passive mode.
      • If the ip pim passive command is configured on an interface enabled for IP multicast, the device will operate this interface in PIM passive mode, which means that the device will not send PIM messages on the interface nor will it accept PIM messages from other devices across this interface. The device will instead consider that it is the only PIM device on the network and thus act as the DR and also as the DF for all bidir-PIM group ranges. IGMP operations are unaffected by this command.
        Note   

        Do not use this command on LANs that have more than one multicast device connected to them because all devices with this command configured will consider themselves to be DR/DF, resulting in duplicate traffic (PIM-SM, PIM-DM, PIM-SSM) or even in looping traffic (bidir-PIM). Instead, use the ip pim neighbor-filter command to limit PIM messages to and from valid devices on LANs with more than one device.

    • The second sample shows how to restrict a PIM neighbor from participating in PIM by filtering all PIM control messages that match the access list specified for the access-list argument.
      Note   

      The ip pim neighbor-filtercommand does not filter Auto-RP announcements and is intended only to filter control messages between PIM neighbors.

    Note   

    The ip pim passive and ip pim neighbor-filter commands can be used together on an interface. If both commands are configured, the ip pim passive command will take precedence over the ip pim neighbor-filter command.

     
    Step 5 ip igmp helper-address ip-address


    Example: 
    Device(config-if)# ip igmp helper-address 172.16.32.1
     

    Configures the device to forward all IGMP host reports and leave messages received on the interface to the specified IP address.

    • The IGMP host reports and leave messages are forwarded to the IP address specified for the ip-addressargument, using the source address of the next hop interface.
    • This command enables a type of “dense-mode” join, allowing stub sites not participating in PIM to indicate membership in IP multicast groups.
     
    Step 6 end


    Example: 
    Device(config-if)# end
     

    Returns to privileged EXEC mode.

     
    Step 7 show ip pim interface [type number]


    Example: 
    Device# show ip pim interface
     

    Displays information about interfaces configured for PIM.

    • Use this command to confirm the mode in which the PIM interfaces are operating.
     

    Configuring the Distribution Device for Multicast Stub Routing

    Perform the following task to configure the distribution device for multicast stub routing.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    interface type number

      4.    Do one of the following:

      • ip pim passive
      • ip pim neighbor-filter access-list

      5.    end

      6.    show ip pim interface [type number]


    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 GigabitEthernet0/0
       

      Enters interface configuration mode.

       
      Step 4 Do one of the following:
      • ip pim passive
      • ip pim neighbor-filter access-list


      Example: 
      Device(config-if)# ip pim passive


      Example: 
      Device(config-if)# ip pim neighbor-filter 1
       
      • The first sample shows how to configure the interface to operate in PIM passive mode.
        • If the ip pim passive command is configured on an interface enabled for IP multicast, the device will operate this interface in PIM passive mode, which means that the device will not send PIM messages on the interface nor will it accept PIM messages from other devices across this interface. The device will instead consider that it is the only PIM device on the network and thus act as the DR and also as the DF for all bidir-PIM group ranges. IGMP operations are unaffected by this command.
          Note   

          Do not use this command on LANs that have more than one multicast device connected to them because all devices with this command configured will consider themselves to be DR/DF, resulting in duplicate traffic (PIM-SM, PIM-DM, PIM-SSM) or even in looping traffic (bidir-PIM). Instead, use the ip pim neighbor-filter command to limit PIM messages to and from valid devices on LANs with more than one device.

      • The second sample shows how to restrict a PIM neighbor from participating in PIM by filtering all PIM control messages that match the access list specified for the access-list argument.
        Note   

        The ip pim neighbor-filtercommand does not filter Auto-RP announcements and is intended only to filter control messages between PIM neighbors.

      Note   

      The ip pim passive and ip pim neighbor-filter commands can be used together on an interface. If both commands are configured, the ip pim passive command will take precedence over the ip pim neighbor-filter command.

       
      Step 5 end


      Example: 
      Device(config-if)# end
       

      Returns to privileged EXEC mode.

       
      Step 6 show ip pim interface [type number]


      Example: 
      Device# show ip pim interface
       

      Displays information about interfaces configured for PIM.

      • Use this command to confirm the mode in which PIM interfaces are operating.
       

      Configuration Examples for Implementing Multicast Stub Routing

      Example: Implementing Multicast Stub Routing - PIM-DM

      The following example shows the configuration of multicast stub routing in a PIM-DM environment. The example is based on the topology shown in the figure.

      Figure 1. Multicast Stub Routing Example Topology (PIM-DM)

      Distribution Device Configuration

      ip multicast-routing
!
interface GigabitEthernet1/0
  ip pim sparse-dense-mode
  ip pim neighbor-filter 1 (or ip pim passive)
!
access-list 1 deny any

      Stub Device Configuration

      ip multicast-routing
!
interface Vlan100
  ip pim sparse-dense-mode
  ip igmp helper-address 172.16.32.1
  ip pim passive
!
interface GigabitEthernet1/0
  ip pim sparse-dense-mode

      Example: Implementing Multicast Stub Routing - PIM-SM Static RP

      The following example shows the configuration of multicast stub routing in a PIM-SM environment using static RP. The example is based on the topology shown in the figure.

      Figure 2. Multicast Stub Routing Example Topology (PIM-SM, Static RP)

      Distribution Device Configuration

      ip multicast-routing
!
Interface GigabitEthernet1/0
  ip pim sparse-mode
  ip pim neighbor-filter 1 (or ip pim passive)
!
access-list 1 deny any
!
ip pim rp-address 10.1.1.1

      Stub Device Configuration 

      ip multicast-routing
!
interface Vlan100
  ip pim sparse-mode
  ip igmp helper-address 172.16.32.1
  ip pim passive
!
interface GigabitEthernet1/0
  ip pim sparse-mode
!
ip pim rp-address 10.1.1.1

      Example: Implementing Multicast Stub Routing - PIM-SSM

      The following example shows the configuration of multicast stub routing in a PIM-SSM environment. The example is based on the topology shown in the figure.

      Figure 3. Multicast Stub Routing Example Topology (PIM-SSM)

      Distribution Device Configuration

      ip multicast-routing
!
interface GigabitEthernet1/0
  ip pim sparse-mode
  ip pim neighbor-filter 1 (or ip pim passive)
!
access-list 1 deny any
!
ip pim ssm default

      Stub Device Configuration

      ip multicast-routing
!
interface Vlan100
  ip pim sparse-mode
  ip igmp helper-address 172.16.32.1
  ip pim passive
!
interface GigabitEthernet1/0
  ip pim sparse-mode
!
ip pim ssm default

      Example Implementing Multicast Stub Routing - Bidir-PIM

      The following example shows the configuration of multicast stub routing in a bidir-PIM environment using static RP. The example is based on the topology shown in the figure.

      Figure 4. Multicast Stub Routing Example Topology (Bidir-PIM)

      Distribution Device Configuration

      ip multicast-routing
!
interface GigabitEthernet1/0
  ip pim sparse-mode
  ip pim neighbor-filter 1 (or ip pim passive)
!
access-list 1 deny any
!
ip pim bidir-enable
ip pim rp-address 10.1.1.1 bidir

      Stub Device Configuration

      ip multicast-routing
!
interface Vlan100
  ip pim sparse-mode
  ip igmp helper-address 172.16.32.1
  ip pim passive
!
interface GigabitEthernet1/0
  ip pim sparse-mode
!
ip pim bidir-enable
ip pim rp-address 10.1.1.1 bidir

      Additional References

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Commands List, All Releases

      Cisco IOS IP SLAs commands

      Cisco IOS IP Multicast Command Reference

      Overview of the IP multicast technology area

      “ IP Multicast Technology Overview ” module

      Concepts, tasks, and examples for configuring an IP multicast network using PIM

      “ Configuring a Basic IP Multicast Network ” module

      Standards and RFCs

      Standard/RFC

      Title

      No new or modified standards or RFCs are supported by this feature.

      --

      MIBs

      MIB

      MIBs Link

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

      To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

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

      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 Implementing Multicast Stub Routing

      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 Implementing Multicast Stub Routing

      Feature Name

      Releases

      Feature Information

      PIM Stub

      12.2(37)SE

      15.0(1)M

      12.2(33)SRE

      Cisco IOS XE 3.1.0SG

      The PIM Stub feature introduces the capability to configure an interface to operate in PIM passive mode, which means that the router will not send PIM messages on the interface nor will it accept PIM messages from other routers across this interface. The router will instead consider that is is the only PIM router on the network and thus act as the DR and also as the DF (for all bidir-PIM group ranges). This mode is used primarily in multicast stub routing scenarios.

      The following commands were introduced or modified: ip pim passive.