Configuring Mutlicast Stub Routing

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.

  • This feature is not supported on the C9500-12Q, C9500-16X, C9500-24Q, C9500-40X models of the Cisco Catalyst 9500 Series Switches.

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

Multicast stub routing can be used on two types of links for multicast stub networks:

  • Upstream link between the stub and distribution devices--The stub device’s interface facing the distribution device has full PIM functionality; a distribution device’s interface facing the stub device does not and relies on a PIM neighbor filter or operates in PIM passive mode.

  • Downstream link between the stub device and interested receiver--Downstream links are connected to Layer 2 access domains, such as VLANs, or Layer 3 routed interfaces. The downstream link operates in PIM passive mode and assumes that it is the only interface on that access domain, making it the Designated Router (DR). If PIM passive mode is not supported, the downstream link relies on a PIM neighbor filter to prevent the stub device from discovering other PIM neighbors on that interface. In addition, an Interior Group Management Protocol (IGMP) helper is used to proxy IGMP reports to the distribution device’s link facing the stub device.

Multicast Stub Routing Between Stub and Distribution Devices

Implementing multicast stub routing between the stub and distribution device in PIM sparse mode (PIM-SM) environment 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 device to the stub device. It is possible to have sources directly connected to the stub network, and, 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).

  • 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 non-redundant stub network topologies.

Configuring Multicast Stub Routing

Prerequisites

  • The tasks in this section assume that IP multicast has been enabled and that the PIM interfaces have been configured using the tasks described in the “ Configuring Basic IP Multicast ” module.

Restrictions

  • Multicast stub routing does not prevent the configuration of other IGPs that do not support stub routing, such as RIP, OSPF, and 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 EIGRP stub routing configuration will assist in multicast stub routing.

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

Configuring the Stub Device for Multicast Stub Routing

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

Procedure

  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. 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-SSM) or even in looping traffic. 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-filter command 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-address argument, 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.

Procedure

  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. 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-SSM) or even in looping traffic. 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-filter command 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-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 1. 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 2. 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

Feature Information for 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 https://cfnng.cisco.com/. An account on Cisco.com is not required.
Table 1. Feature Information for PIM

Release

Feature Description

Cisco IOS XE Fuji 16.8.1a

This feature was introduced.