Table Of Contents
Implementing Multicast Stub Routing
Prerequisites for Multicast Stub Routing
Restrictions for Multicast Stub Routing
Information About Multicast Stub Routing
Multicast Stub Routing Between Stub and Distribution Routers
Multicast Stub Routing Between the Stub Router and Interested Receivers
Benefits of Multicast Stub Routing
How to Implement Multicast Stub Routing
Implementing Multicast Stub Routing
Configuring the Stub Router for Multicast Stub Routing
Configuring the Distribution Router for Multicast Stub Routing
Configuration Examples for Implementing Multicast Stub Routing
Examples: Implementing Multicast Stub Routing
Example: Implementing Multicast Stub Routing (PIM-DM)
Example: Implementing Multicast Stub Routing (PIM-SM, Static RP)
Example: Implementing Multicast Stub Routing (PIM-SSM)
Example: Implementing Multicast Stub Routing (Bidir-PIM)
Feature Information for Implementing Multicast Stub Routing
Implementing Multicast Stub Routing
First Published: October 2, 2009Last Updated: September 10, 2010This 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 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 for Implementing Multicast Stub Routing" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•Prerequisites for Multicast Stub Routing
•Restrictions for Multicast Stub Routing
•Information About Multicast Stub Routing
•How to Implement Multicast Stub Routing
•Configuration Examples for Implementing Multicast Stub Routing
•Feature Information for Implementing Multicast Stub Routing
Prerequisites for Multicast Stub Routing
•Before performing the tasks in this module, you should be familiar with the concepts explained in the "IP Multicast Technology Overview" module.
•The tasks in this module 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 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.
•Multicast stub routing can be only implemented in nonredundant stub network topologies.
Information About Multicast Stub Routing
•Benefits of 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. The Cisco IOS software allows only the configuration of nonredundant multicast stub networks with the use of multicast stub routing.
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 router—The stub router's interface facing the distribution router has full PIM functionality; a distribution router's interface facing the stub router does not and relies on a PIM neighbor filter or operates in PIM passive mode.
•Downstream link between the stub router 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). In Cisco IOS releases that do not support PIM passive mode, the downstream link relies on a PIM neighbor filter to prevent the stub router 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 router's link facing the stub router.
Multicast Stub Routing Between Stub and Distribution Routers
Implementing multicast stub routing between the stub and distribution router 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 router 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 router, 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 router. 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 router will be filtered by the PIM neighbor filter applied on the distribution router, resulting in reverse path forwarding (RPF) failures. Furthermore, receivers must be directly connected to the stub router and cannot be further downstream.
Multicast Stub Routing Between the Stub Router and Interested Receivers
Implementing multicast stub routing between the stub router 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 router, 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
This section contains the following tasks:
•Implementing Multicast Stub Routing (required)
Implementing Multicast Stub Routing
Perform the following tasks to implement multicast stub routing:
•Configuring the Stub Router for Multicast Stub Routing (required)
•Configuring the Distribution Router for Multicast Stub Routing (required)
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.
Note For more information about configuring unicast EIGRP stub routing, see the "Configuring EIGRP" module.
•Multicast stub routing can only be implemented in nonredundant stub network topologies.
Configuring the Stub Router for Multicast Stub Routing
Perform this task to configure a stub router for multicast stub routing.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip pim passive
or
ip pim neighbor-filter access-list5. ip igmp helper-address ip-address
6. end
7. show ip pim interface [type number]
DETAILED STEPS
Configuring the Distribution Router for Multicast Stub Routing
Perform the following task to configure the distribution router for multicast stub routing.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip pim passive
or
ip pim neighbor-filter access-list5. end
6. show ip pim interface [type number]
DETAILED STEPS
Configuration Examples for Implementing Multicast Stub Routing
This section contains the following example:
•Examples: Implementing Multicast Stub Routing
Examples: Implementing Multicast Stub Routing
This section contains the following examples for implementing multicast stub routing. The examples provide the configurations for both multicast stub routing using a PIM neighbor filter and an IGMP helper and using a PIM passive interface.
•Example: Implementing Multicast Stub Routing (PIM-DM)
•Example: Implementing Multicast Stub Routing (PIM-SM, Static RP)
•Example: Implementing Multicast Stub Routing (PIM-SSM)
•Example: Implementing Multicast Stub Routing (Bidir-PIM)
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 Figure 1.
Figure 1 Multicast Stub Routing Example Topology (PIM-DM)
Distribution Router Configuration
ip multicast-routing!interface GigabitEthernet1/0ip pim sparse-dense-modeip pim neighbor-filter 1 (or ip pim passive)!access-list 1 deny anyStub Router Configuration
ip multicast-routing!interface Vlan100ip pim sparse-dense-modeip igmp helper-address 172.16.32.1ip pim passive!interface GigabitEthernet1/0ip pim sparse-dense-modeExample: 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 Figure 2.
Figure 2 Multicast Stub Routing Example Topology (PIM-SM, Static RP)
Distribution Router Configuration
ip multicast-routing!Interface GigabitEthernet1/0ip pim sparse-modeip pim neighbor-filter 1 (or ip pim passive)!access-list 1 deny any!ip pim rp-address 10.1.1.1Stub Router Configuration
ip multicast-routing!interface Vlan100ip pim sparse-modeip igmp helper-address 172.16.32.1ip pim passive!interface GigabitEthernet1/0ip pim sparse-mode!ip pim rp-address 10.1.1.1Example: 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 Figure 3.
Figure 3 Multicast Stub Routing Example Topology (PIM-SSM)
Distribution Router Configuration
ip multicast-routing!interface GigabitEthernet1/0ip pim sparse-modeip pim neighbor-filter 1 (or ip pim passive)!access-list 1 deny any!ip pim ssm defaultStub Router Configuration
ip multicast-routing!interface Vlan100ip pim sparse-modeip igmp helper-address 172.16.32.1ip pim passive!interface GigabitEthernet1/0ip pim sparse-mode!ip pim ssm defaultExample: 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 Figure 4.
Figure 4 Multicast Stub Routing Example Topology (Bidir-PIM)
Distribution Router Configuration
ip multicast-routing!interface GigabitEthernet1/0ip pim sparse-modeip pim neighbor-filter 1 (or ip pim passive)!access-list 1 deny any!ip pim bidir-enableip pim rp-address 10.1.1.1 bidirStub Router Configuration
ip multicast-routing!interface Vlan100ip pim sparse-modeip igmp helper-address 172.16.32.1ip pim passive!interface GigabitEthernet1/0ip pim sparse-mode!ip pim bidir-enableip pim rp-address 10.1.1.1 bidirAdditional References
Related Documents
Related Topic Document TitleOverview of the IP multicast technology area
"IP Multicast Technology Overview" module
Concepts, tasks, and examples for configuring an IP multicast network using PIM
IP multicast commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples
Standards
Standard TitleNo new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
RFC TitleNo new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.
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Technical Assistance
Feature Information for Implementing Multicast Stub Routing
Table 1 lists the features in this module and provides links to specific configuration information.
For information on a feature in this technology that is not documented here, see the "IP Multicast Features Roadmap."
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 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.
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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.
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