Cisco IOS XR Multicast Configuration Guide, Release 3.3 - Implementing Multicast Routing on Cisco IOS XR Software [Cisco IOS XR Software]

Table Of Contents

Implementing Multicast Routing on Cisco IOS XR Software

Contents

Prerequisites for Implementing Multicast Routing on Cisco IOS XR Software

Information About Implementing Multicast Routing on Cisco IOS XR Software

Key Protocols and Features Supported in the Cisco IOS XR software Multicast Routing Implementation

Multicast Routing Functional Overview

Cisco IOS XR Multicast Routing Implementation

Internet Group Management Protocol and Multicast Listener Discovery

IGMP/MLD Versions

IGMP Routing Example

Protocol Independent Multicast

PIM-Sparse Mode

PIM-Source Specific Multicast

PIM Shared Tree and Source Tree (Shortest Path Tree)

Designated Routers

Rendezvous Points

Auto-RP

PIM Bootstrap Router

Reverse Path Forwarding

Multicast Source Discovery Protocol

Multicast Nonstop Forwarding

Multicast Quality of Service

Multicast Configuration Submodes

Multicast-routing Configuration Submode

Router PIM Configuration Submode

Router IGMP Configuration Submode

Router MLD Configuration Submode

Router MDSP Configuration Submode

Understanding Interface Configuration Inheritance

Understanding Enabling and Disabling Interfaces

How to Implement Multicast on Cisco IOS XR Software

Configuring PIM-SM and PIM-SSM

PIM-SM Operations

PIM-SSM Operations

Restrictions

Configuring a Static RP and Allowing Backward Compatibility

Configuring Auto-RP to Automate Group-to-RP Mappings

Configuring the BSR

Configuring Multicast Nonstop Forwarding

Prerequisites

Interconnecting PIM-SM Domains with MSDP

Prerequisites

Controlling Source Information on MSDP Peer Routers

Configuring Multicast Quality of Service

Configuration Examples for Implementing Multicast Routing on Cisco IOS XR Software

MSDP Anycast RP Configuration on Cisco IOS XR Software: Example

Bidir-PIM Configuration on Cisco IOS XR Software: Example

Preventing Auto-RP Messages from Being Forwarded on Cisco IOS XR Software: Example

Inheritance in MSDP on Cisco IOS XR Software: Example

Multicast QoS: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Implementing Multicast Routing on Cisco IOS XR Software

Multicast routing is a bandwidth-conserving technology that reduces traffic by simultaneously delivering a single stream of information to potentially thousands of corporate recipients and homes. Applications that take advantage of multicast include video conferencing, corporate communications, distance learning, and distribution of software, stock quotes, and news.

This document assumes that you are familiar with IPv4 and IPv6 multicast routing configuration tasks and concepts for Cisco IOS XR software.

Multicast routing allows a host to send packets to a subset of all hosts as a group transmission rather than to a single host, as in unicast transmission, or to all hosts, as in broadcast transmission. The subset of hosts is known as group members and are identified by a single multicast group address that falls under the IP Class D address range from 224.0.0.0 through 239.255.255.255.

For detailed conceptual information about multicast routing and complete descriptions of the multicast routing commands listed in this module, you can refer to the "Related Documents" section of this module. To locate documentation for other commands that might appear in the course of executing a configuration task, search online in the Cisco IOS XR software master command index.

Feature History for Configuring Multicast Routing on Cisco IOS XR Software

Release

Modification

Release 2.0

This feature was introduced on the Cisco CRS-1 router.

Release 3.0

No modification.

Release 3.2

Support was added for the Cisco XR 12000 Series Router.

Support was added for the IPv6 routing protocol on the Cisco CRS-1 router.

Support was added for the bootstrap router (BSR) feature.

Release 3.3.0

Conceptual information for quality of service (QoS) was added.

Contents

•Prerequisites for Implementing Multicast Routing on Cisco IOS XR Software

•Information About Implementing Multicast Routing on Cisco IOS XR Software

•How to Implement Multicast on Cisco IOS XR Software

•Configuration Examples for Implementing Multicast Routing on Cisco IOS XR Software

•Additional References

Prerequisites for Implementing Multicast Routing on Cisco IOS XR Software

The following prerequisites are required to implement multicast routing on your multicast network:

•You must install and activate a Package Installation Envelope (PIE) for the multicast routing software.

For detailed information about optional PIE installation, refer to the Cisco CRS-1 Series Carrier Routing System Getting Started Guide.

•You must be in a user group associated with a task group that includes the proper task IDs for multicast routing commands. Task IDs for commands are listed in the Cisco IOS XR Task ID Reference Guide.

For detailed information about user groups and task IDs, see the Configuring AAA Services on Cisco IOS-XR Software module of the Cisco IOS-XR System Security Configuration Guide.

•You must be familiar with IPv4 and IPv6 multicast routing configuration tasks and concepts.

Information About Implementing Multicast Routing on Cisco IOS XR Software

To implement multicast routing features in this document you must understand the following appropriate concepts:

•Key Protocols and Features Supported in the Cisco IOS XR software Multicast Routing Implementation

•Multicast Routing Functional Overview

•Internet Group Management Protocol and Multicast Listener Discovery

•Protocol Independent Multicast

•PIM Shared Tree and Source Tree (Shortest Path Tree)

•Designated Routers

•Rendezvous Points

•Auto-RP

•PIM Bootstrap Router

•Reverse Path Forwarding

•Multicast Source Discovery Protocol

•Multicast Nonstop Forwarding

•Multicast Quality of Service

•Multicast Configuration Submodes

•Understanding Interface Configuration Inheritance

•Understanding Enabling and Disabling Interfaces

Key Protocols and Features Supported in the Cisco IOS XR software Multicast Routing Implementation

Table 2 lists the supported features for IPv4 and IPv6 multicast routing in Cisco IOS XR software.

Table 2 Supported features for IPv4 and IPv6

Feature

IPv4 support

IPv6 support

Dynamic host registration

Yes (IGMP v1/2/3)

Yes (MLD v1/2)

Explicit tracking of hosts, groups, and channels

Yes (IGMP v3)

Yes (MLD v2)

PIM-SM¹

Yes

Yes

PIM-SSM²

Yes

Yes

Auto-RP

Yes

No

BSR³

Yes

Yes

MSDP⁴

Yes

No

BGP⁵

Yes

Yes

Multicast NSF⁶

Yes

Yes

OOR handling⁷

Yes

Yes

¹Protocol Independent Multicast in sparse mode

²Protocol Independent Multicast in Source-Specific Multicast

³PIM bootstrap router

⁴Multicast Source Discovery Protocol

⁵Multiprotocol Border Gateway Protocol

⁶Nonstop forwarding

⁷Out of resource

Multicast Routing Functional Overview

Traditional IP communication allows a host to send packets to a single host (unicast transmission) or to all hosts (broadcast transmission). Multicast provides a third scheme, allowing a host to send a single data stream to a subset of all hosts (group transmission) at about the same time. IP hosts are known as group members.

Packets delivered to group members are identified by a single multicast group address. Multicast packets are delivered to a group using best-effort reliability, just like IP unicast packets.

The multicast environment consists of senders and receivers. Any host, regardless of whether it is a member of a group, can send to a group. However, only the members of a group receive the message.

A multicast address is chosen for the receivers in a multicast group. Senders use that group address as the destination address of a datagram to reach all members of the group.

Membership in a multicast group is dynamic; hosts can join and leave at any time. There is no restriction on the location or number of members in a multicast group. A host can be a member of more than one multicast group at a time.

How active a multicast group is and what members it has can vary from group to group and from time to time. A multicast group can be active for a long time, or it may be very short-lived. Membership in a group can change constantly. A group that has members may have no activity.

Routers use the IGMP (IPv4) and MLD (IPv6) to learn whether members of a group are present on their directly attached subnets. Hosts join multicast groups by sending IGMP or MLD report messages.

Many multimedia applications involve multiple participants. Multicast is naturally suitable for this communication paradigm.

Cisco IOS XR Multicast Routing Implementation

Cisco IOS XR software supports the following protocols to implement multicast routing:

•IGMP and MLD are used (depending on the IP protocol) between hosts on a LAN and the routers on that LAN to track the multicast groups of which hosts are members.

•PIM-SM is used between routers so that they can track which multicast packets to forward to each other and to their directly connected LANs.

•PIM-SSM is similar to PIM-SM with the additional ability to report interest in receiving packets from specific source addresses (or from all but the specific source addresses), to an IP multicast address.

•PIM-SSM is made possible by IGMPv3 and MLDv2. Hosts can now indicate interest in specific sources using IGMPv3 and MLDv2. SSM does not require a rendezvous point (RP) to operate.

Figure 1 shows IGMP/MLD and PIM-SM operating in a multicast environment.

Figure 1 Multicast Routing Protocols Supported for Cisco IOS XR Software

Internet Group Management Protocol and Multicast Listener Discovery

Cisco IOS XR software provides support for

•Internet Group Management Protocol (IGMP) over IPv4, and

•Multicast Listener Discovery (MLD) over IPv6.

IGMP and MLD provide a means for hosts to indicate which multicast traffic they are interested in and for routers to control and limit the flow of multicast traffic throughout the network. Routers build state by means of IGMP/MLD messages: router queries and host reports.

A set of queries and hosts that receive multicast data streams from the same source is called a multicast group. Hosts use IGMP/MLD messages to join and leave multicast groups.

Note IGMP messages use group addresses, which are Class D IP addresses. The high-order four bits of a
Class D address are 1110. Host group addresses can be in the range 224.0.0.0 to 239.255.255.255. The address 224.0.0.0 is guaranteed not to be assigned to any group. The address 224.0.0.1 is assigned to all systems on a subnet. The address 224.0.0.2 is assigned to all routers on a subnet.

IGMP/MLD Versions

The following points describe IGMP versions 1, 2, and 3:

•IGMP Version 1 provides for the basic query-response mechanism that allows the multicast router to determine which multicast groups are active and for other processes that enable hosts to join and leave a multicast group.

•IGMP Version 2 extends IGMP allowing such features as the IGMP query timeout and the maximum query-response time. See RFC 2236.

Note MLDv1 provides the same functionality (under IPv6) as IGMP Version 2.

•IGMP Version 3 permits joins and leaves for certain source/group pairs instead of requesting traffic from all sources in the multicast group.

Note MLDv2 provides the same functionality (under IPv6) as IGMP Version 3.

IGMP Routing Example

Figure 2 illustrates two sources, 10.0.0.1 and 10.0.1.1, that are multicasting to group 239.1.1.1. The receiver wants to receive traffic addressed to group 239.1.1.1 from source 10.0.0.1 but not from Source 10.0.1.1. The host must send an IGMPv3 message containing a list of sources and groups (S, G)s that it wants to join and a list of sources and groups (S, G)s that it wants to leave. Router C can now use this information to prune traffic from Source 10.0.1.1 so that only Source 10.0.0.1 traffic is being delivered to
Router C.

Figure 2 IGMPv3 Signaling

Note When configuring IGMP, ensure that all systems on the subnet support the same IGMP version. The router does not automatically detect Version 1 systems. Configure the router for Version 2 if your hosts do not support Version 3.

Protocol Independent Multicast

PIM is an efficient IP routing protocol that is independent of the unicast routing table to perform send and receive multicast route updates like other protocols, such as Multicast Open Shortest Path First (MOSPF) or Distance Vector Multicast Routing Protocol (DVMRP). In other words, regardless of which unicast routing protocols are being used in the LAN to populate the unicast routing table, Cisco IOS XR PIM implementation leverages the existing unicast table content to perform the Reverse Path Forwarding (RPF) check function instead of building and maintaining its own separate multicast route table.

PIM is defined in RFC 2362, Protocol-Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification. For more information, see the following Internet Engineering Task Force (IETF) Internet drafts:

•Protocol Independent Multicast (PIM): Motivation and Architecture

•Protocol Independent Multicast (PIM), Sparse Mode Protocol Specification

Note Cisco IOS XR software supports PIM SM, PIM SSM, and PIM Version 2 only. PIM Version 1 hello messages that arrive from neighbors are rejected.

PIM-Sparse Mode

Typically, PIM in sparse mode operation is used in a multicast network when relatively few routers are involved in each multicast and these routers do not forward multicast packets for a group, unless there is an explicit request for the traffic. Requests are accomplished using PIM join messages, which are sent hop by hop toward the root node of the tree. The root node of a tree in PIM-SM is the RP in the case of a shared tree or the first-hop router that is directly connected to the multicast source in the case of a shortest path tree (SPT). The RP keeps track of multicast groups and the hosts that send multicast packets are registered with the RP by that host's first-hop router.

How does PIM-SM work? As a PIM join travels up the tree, routers along the path set up multicast forwarding state so that the requested multicast traffic is forwarded back down the tree. When multicast traffic is no longer needed, a router sends a PIM prune message up the tree toward the root node to prune (or remove) the unnecessary traffic. As this PIM prune travels hop by hop up the tree, each router updates its forwarding state appropriately. Ultimately, the forwarding state associated with a multicast group or source is removed.

PIM-SM is the best choice for multicast networks that have potential members at the end of WAN links.

PIM-Source Specific Multicast

PIM-SSM is the routing protocol that supports the implementation of SSM and is derived from PIM-SM. However, unlike PIM-SM where all multicast sources are sent when there is a PIM join, the SSM feature forwards datagram traffic to receivers from only those multicast sources that the receivers have explicitly joined; thus optimizing bandwidth utilization and denying unwanted Internet broadcast traffic. Further, instead of the use of RP and shared trees, SSM uses information found on source addresses for a multicast group. This information is provided by receivers through the source addresses relayed to the last-hop routers by IGMPv3 membership reports resulting in source-specific trees.

In SSM, delivery of datagrams is based on (S, G) channels. Traffic for one (S, G) channel consists of datagrams with an IP unicast source address S and the multicast group address G as the IP destination address. Systems will receive this traffic by becoming members of the (S, G) channel. Signaling is not required, but receivers must subscribe or unsubscribe to (S, G) channels to receive or not receive traffic from specific sources. Channel subscription signaling uses IGMP include mode membership reports, which are supported only in Version 3 of IGMP (IGMPv3).

To run SSM with IGMPv3, SSM must be supported on the multicast router, the host where the application is running, and the application itself. Cisco IOS XR software allows SSM configuration for an arbitrary subset of the IP multicast address range 224.0.0.0 through 239.255.255.255. When an SSM range is defined, existing IP multicast receiver applications will not receive any traffic when they try to use addresses in the SSM range unless the application is modified to use explicit (S,G) channel subscription.

PIM Shared Tree and Source Tree (Shortest Path Tree)

By default, members of a group receive data from senders to the group across a single data distribution tree rooted at the RP. This type of distribution tree is called a shared tree or rendezvous point tree (RPT) as illustrated in Figure 3. Data from senders is delivered to the RP for distribution to group members joined to the shared tree.

Figure 3 Shared Tree and Source Tree (Shortest Path Tree)

If the data threshold warrants, leaf routers on the shared tree may initiate a switch to the data distribution tree rooted at the source. This type of distribution tree is called a shortest path tree or source tree. By default, the Cisco IOS XR software switches to a source tree upon receiving the first data packet from a source.

The following process describes the move from shared tree to source tree in more detail:

1. Receiver joins a group; leaf Router C sends a join message toward RP.

2. RP puts link to Router C in its outgoing interface list.

3. Source sends data; Router A encapsulates data in Register and sends it to RP.

4. RP forwards data down the shared tree to Router C and sends a join message toward Source. At this point, data may arrive twice at the RP, once encapsulated and once natively.

5. When data arrives natively (unencapsulated) at RP, RP sends a register-stop message to Router A.

6. By default, receipt of the first data packet prompts Router C to send a join message toward Source.

7. When Router C receives data on (S,G), it sends a prune message for Source up the shared tree.

8. RP deletes the link to Router C from outgoing interface of (S,G). RP triggers a prune message toward Source.

Join and prune messages are sent for sources and RPs. They are sent hop by hop and are processed by each PIM router along the path to the source or RP. Register and register-stop messages are not sent hop by hop. They are sent by the designated router that is directly connected to a source and are received by the RP for the group.

Tip The spt-threshold infinity command lets you configure the router so that it never switches to the SPT.

Designated Routers

Cisco routers use PIM-SM to forward multicast traffic and follow an election process to select a designated router (DR) when there is more than one router on a LAN segment.

The designated router is responsible for sending PIM register and PIM join and prune messages toward the RP to inform it about host group membership.

If there are multiple PIM-SM routers on a LAN, a designated router must be elected to avoid duplicating multicast traffic for connected hosts. The PIM router with the highest IP address becomes the DR for the LAN unless you choose to force the DR election by use of the dr-priority command. The DR priority option will allow you to specify the DR priority of each router on the LAN segment (default priority = 1) so that the router with the highest priority is elected as the DR. If all routers on the LAN segment have the same priority, the highest IP address is again used as the tiebreaker.

Figure 4 illustrates what happens on a multiaccess segment. Router A (10.0.0.253) and Router B (10.0.0.251) are connected to a common multiaccess Ethernet segment with Host A (10.0.0.1) as an active receiver for Group A. As the Explicit Join model is used, only Router A, operating as the DR, sends joins to the RP to construct the shared tree for Group A. If Router B was also permitted to send (*, G) joins to the RP, parallel paths are created and Host A receive duplicate multicast traffic. Once Host A begins to source multicast traffic to the group, the DR's responsibility is to send register messages to the RP. Again, if both routers were assigned the responsibility, the RP receives duplicate multicast packets.

What happens if the DR fails? The PIM-SM provides a way to detect the failure of Router A and elect a failover DR. If the DR (Router A) became inoperable, Router B detects this situation when its neighbor adjacency with Router A timed out. As Router B has been hearing IGMP Membership Reports from Host A, it already has IGMP state for Group A on this interface and immediately sends a join to the RP when it became the new DR. This step reestablishes traffic flow down a new branch of the shared tree using Router B. Additionally, if Host A were sourcing traffic, Router B initiates a new Register process immediately after receiving the next multicast packet from Host A. This action triggers the RP to join the SPT to Host A using a new branch through Router B.

Tip Two PIM routers are neighbors if there is a direct connection between them. To display your PIM neighbors, use the show pim neighbor EXEC command.

Figure 4 Designated Router Election on a Multiaccess Segment

Note DR election process is required only on multiaccess LANs. The last-hop router directly connected to the host is the DR.

Rendezvous Points

When PIM is configured in sparse mode, you must choose one or more routers to operate as a rendezvous point (RP). An RP is a single common root placed at a chosen point of a shared distribution tree, as illustrated in Figure 3. An RP can either be configured statically in each box, or learned through a dynamic mechanism.

PIM DRs forward data from directly connected multicast sources to the RP for distribution down the shared tree. Data is forwarded to the RP in one of two ways:

1. Encapsulated in register packets and unicast directly to the RP by the first-hop router operating as the DR.

2. If the RP has itself joined the source tree, it is multicast forwarded per the RPF forwarding algorithm described in the "Reverse Path Forwarding" section.

The RP address is used by first-hop routers to send PIM register messages on behalf of a host sending a packet to the group. The RP address is also used by last-hop routers to send PIM join and prune messages to the RP to inform it about group membership. You must configure the RP address on all routers (including the RP router).

A PIM router can be an RP for more than one group. Only one RP address can be used at a time within a PIM domain. The conditions specified by the access list determine for which groups the router is an RP.

You can manually configure a PIM router to function as an RP or allow the RP to learn group-to-RP mappings automatically by configuring Auto-RP or BSR (see "Auto-RP" and "PIM Bootstrap Router").

Auto-RP

Auto-RP is a feature that automates the distribution of group-to-RP mappings in a PIM network. This feature has the following benefits:

•It is easy to use multiple RPs within a network to serve different group ranges.

•It allows load splitting among different RPs and arrangement of RPs according to the location of group participants.

•It avoids inconsistent, manual RP configurations that can cause connectivity problems.

Multiple RPs can be used to serve different group ranges or serve as hot backups of each other. To ensure that Auto-RP functions, configure routers as candidate RPs so that they can announce their interest in operating as the RP for certain group ranges. Additionally, a router must be designated as an RP-mapping agent that receives the RP-announcement messages from the candidate RPs and arbitrates conflicts. The RP-mapping agent sends the consistent group-to-RP mappings to all remaining routers. Thus, all routers automatically discover which RP to use for the groups they support.

Tip By default, if a given group address is covered by group-to-RP mappings from both static RP configuration and is discovered using Auto-RP or PIM BSR, the Auto-RP or PIM BSR range is preferred. To override the default to use RP mapping only, use the rp-address override keyword.

Note If you configure PIM in sparse mode and do not configure Auto-RP, you must statically configure an RP as described in "Configuring a Static RP and Allowing Backward Compatibility".

When router interfaces are configured in sparse mode, Auto-RP can still be used if all routers are configured with a static RP address for the Auto-RP groups.

Auto-RP is supported under IPv4 only.

PIM Bootstrap Router

The PIM bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution mechanism that simplifies the Auto-RP process. This feature is enabled by default allowing routers to dynamically learn the group-to-RP mappings.

PIM uses the BSR to discover and announce RP-set information for each group prefix to all the routers in a PIM domain. This is the same function accomplished by Auto-RP, but the BSR is part of the PIM Version 2 specification. The BSR mechanism interoperates with Auto-RP on Cisco routers.

To avoid a single point of failure, you can configure several candidate BSRs in a PIM domain. A BSR is elected among the candidate BSRs automatically. Candidates use bootstrap messages to discover which BSR has the highest priority. The candidate with the highest priority sends an announcement to all PIM routers in the PIM domain that it is the BSR.

Routers that are configured as candidate RPs unicast to the BSR the group range for which they are responsible. The BSR includes this information in its bootstrap messages and disseminates it to all PIM routers in the domain. Based on this information, all routers are able to map multicast groups to specific RPs. As long as a router is receiving the bootstrap message, it has a current RP map.

Note BSR is supported under IPv4 only.

Reverse Path Forwarding

RPF is an algorithm used for forwarding multicast datagrams. It functions as follows:

•If a router receives a datagram on an interface it uses to send unicast packets to the source, the packet has arrived on the RPF interface.

•If the packet arrives on the RPF interface, a router forwards the packet out the interfaces present in the outgoing interface list of a multicast routing table entry.

•If the packet does not arrive on the RPF interface, the packet is silently discarded to prevent loops.

PIM uses both source trees and RP-rooted shared trees to forward datagrams; the RPF check is performed differently for each, as follows:

•If a PIM router has source-tree state (that is, an (S, G) entry is present in the multicast routing table), the router performs the RPF check against the IP address of the source of the multicast packet.

•If a PIM router has shared-tree state (and no explicit source-tree state), it performs the RPF check on the RP's address (which is known when members join the group).

Sparse-mode PIM uses the RPF lookup function to determine where it needs to send joins and prunes. (S, G) joins (which are source-tree states) are sent toward the source. (*, G) joins (which are shared-tree states) are sent toward the RP.

Multicast Source Discovery Protocol

MSDP is a mechanism to connect multiple PIM sparse-mode domains. MSDP allows multicast sources for a group to be known to all rendezvous point(s) (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend on RPs in other domains.

An RP in a PIM-SM domain has MSDP peering relationships with MSDP-enabled routers in other domains. Each peering relationship occurs over a TCP connection, which is maintained by the underlying routing system.

MSDP speakers exchange messages called Source Active (SA) messages. When an RP learns about a local active source, typically through a PIM register message, the MSDP process encapsulates the register in a SA message and forwards the information to its peers. The message will contain the source and group information for the multicast flow, as well as any encapsulated data. If a neighboring RP has local joiners for the multicast group, the RP will install the S, G route, forward the encapsulated data contained in the SA message, and send PIM joins back towards the source. This process describes how a multicast path can be built between domains.

Note Although you should configure BGP or Multiprotocol BGP for optimal MSDP interdomain operation, these features are not considered necessary in the Cisco IOS XR software implementation. For information about how BGP or Multiprotocol BGP may be used with MSDP, see the MSDP RPF rules listed in the Multicast Source Discovery Protocol (MSDP), Internet Engineering Task Force (IETF) Internet draft.

Multicast Nonstop Forwarding

The Cisco IOS XR NSF feature for multicast enhances high availability (HA) of multicast packet forwarding. NSF prevents hardware or software failures on the control plane from disrupting the forwarding of existing packet flows through the router.

How does multicast NSF work? The contents of the Multicast Forwarding Information Base (MFIB) is frozen during a control plane failure. Subsequently, PIM attempts to recover normal protocol processing and state before the neighboring routers time out the PIM hello neighbor adjacency for the problematic router. This behavior prevents the NSF-capable router from being transferred to neighbors that will otherwise detect the failure through the timed out adjacency. Routes in MFIB are marked as stale after entering NSF, and traffic continues to be forwarded (based on those routes) until NSF completion. Upon completion, MRIB notifies MFIB and MFIB performs a mark-and-sweep to synchronize MFIB with the current MRIB route info.

Note Non-stop forwarding is not supported for PIM bidirectional routes. If a PIM or MRIB failure (including RP failover) happens with multicast-routing NSF enabled, PIM bidirectional routes in the MFIBs will be purged immediately and forwarding on these routes will stop. Routes will be reinstalled and forwarding will recommence after NSF recovery has ended. This will only impact bidirectional routes. PIM SM/SSM routes are forwarded with NSF during the failure. This exception is designed to prevent possible multicast routing loops from forming when the control plane is not able to participate in the BiDir Designated Forwarder election.

Multicast Quality of Service

Cisco IOS XR software provides for the configuration of multicast QoS. When configured on specific interfaces, system-wide, general QoS operations are applied to multicast traffic as well as general network traffic.

QoS expedites the handling of mission-critical applications, while sharing network resources with noncritical applications. QoS also ensures available bandwidth and minimum delays required by time-sensitive multimedia and voice applications. It also gives network managers control over network applications, improves cost efficiency of WAN connections, and enables advanced differentiated services.

For supported multicast QoS commands, refer to Multicast Routing and Forwarding Commands on Cisco IOS XR Software.

For non-multicast-specific information and examples, refer to Cisco IOS XR Quality of Service Configuration Guide.

Multicast Configuration Submodes

Cisco IOS XR software moves control plane CLI configurations to protocol-specific submodes to provide mechanisms for enabling, disabling, and configuring multicast features on a large number of interfaces.

The Cisco IOS XR software allows you to issue most commands available under submodes as one single command string from global configuration mode.

For example, the ssm command could be executed from the multicast-routing configuration submode like this:
RP/0/RP0/CPU0:router(config)# multicast-routing 
RP/0/RP0/CPU0:router(config-mcast-ipv4)# ssm range
Alternatively, you can issue the same command from global configuration mode like this:
RP/0/RP0/CPU0:router(config)# multicast-routing ssm range
The following multicast protocol-specific submodes are available through these configuration submodes:

•Multicast-routing Configuration Submode

•Router PIM Configuration Submode

•Router IGMP Configuration Submode

•Router MDSP Configuration Submode

Multicast-routing Configuration Submode

When you issue the multicast-routing command, all default multicast components (PIM, IGMP, MLD, MFWD, and MRIB) are automatically started and the CLI prompt changes to "config-mcast-ipv4" indicating that you have entered multicast-routing configuration submode.

In the following sample output, the question mark (?) online help function displays all the commands available under the multicast-routing configuration submode:
RP/0/RP0/CP0:router(config)# multicast-routing
RP/0/RP0/CP0:router(config-mcast-ipv4)# ?
  commit      Commit the configuration changes to running
  default     Set a command to its defaults
  describe    Describe a command without taking real actions
  do          Run an exec command
  exit        Exit from this submode
  interface   Multicast interface configuration subcommands
  mfib        Multicast Forwarding Information Base
  no          Negate a command or set its defaults
  nsf         Global multicast NSF configuration commands
  show        Show contents of configuration
  ssm         Configure a group range for Source-Specific use
  static-rpf  Configure a static RPF rule for a given prefix/mask
Router PIM Configuration Submode

When you issue the router pim command, the CLI prompt changes to "config-pim-ipv4" indicating that you have entered router pim configuration submode.

In the following sample output, the question mark (?) online help function displays all the commands available under the router PIM configuration submode.
RP/0/RP0/CPU0:router(config)# router pim
RP/0/RP0/CPU0:router(config-pim-ipv4)# ?
  accept-register        Registers accept filter
  auto-rp                Auto-RP Commands
  commit                 Commit the configuration changes to running
  default                Set a command to its defaults
  describe               Describe a command without taking real actions
  do                     Run an exec command
  dr-priority            Inherited by all interfaces : PIM Hello DR priority
  exit                   Exit from this submode
  hello-interval         Inherited by all interfaces : Hello interval in seconds
  interface              PIM interface configuration subcommands
  join-prune-interval    Inherited by all interfaces : Join-Prune interval
  neighbor-filter        Neighbor filter
  no                     Negate a command or set its defaults
  nsf                    Configure Non-stop forwarding (NSF) options
  old-register-checksum  Generate registers compatible with older IOS versions
  rp-address             Configure Rendezvous Point
  show                   Show contents of configuration
  spt-threshold          Configure threshold for switching to SPT on last-hop
Router IGMP Configuration Submode

When you issue the router igmp command, the CLI prompt changes to "config-igmp" indicating that you have entered router IGMP configuration submode.

In the following sample output, the question mark (?) online help function displays all the commands available under router IGMP configuration submode:
RP/0/RP0/CP0:router(config)# router igmp
RP/0/RP0/CP0:router(config-igmp)# ? 
  access-group             IGMP group access group
  commit                   Commit the configuration changes to running
  default                  Set a command to its defaults
  describe                 Describe a command without taking real actions
  do                       Run an exec command
  exit                     Exit from this submode
  explicit-tracking        IGMPv3 explicit host tracking
  interface                IGMP interface configuration subcommands
  no                       Negate a command or set its defaults
  nsf                      Configure NSF specific options
  query-interval           IGMP host query interval
  query-max-response-time  IGMP max query response value
  query-timeout            IGMP previous querier timeout
  show                     Show contents of configuration
  version                  IGMP version
Router MLD Configuration Submode

When you issue the router mld command, the CLI prompt changes to "config-mld" indicating that you have entered router MLD configuration submode.

In the following sample output, the question mark (?) online help function displays all the commands available under router MLD configuration submode:
RP/0/RP0/CP0:router(config)# router mld
RP/0/RP0/CP0:router(config-mld)# ? 
  access-group             MLD group access group
  commit                   Commit the configuration changes to running
  default                  Set a command to its defaults
  describe                 Describe a command without taking real actions
  do                       Run an exec command
  exit                     Exit from this submode
  explicit-tracking        MLD explicit host tracking
  interface                MLD interface configuration subcommands
  no                       Negate a command or set its defaults
  nsf                      Configure NSF specific options
  query-interval           MLD host query interval
  query-max-response-time  MLD max query response value
  query-timeout            MLD previous querier timeout
  show                     Show contents of configuration
  version                  MLD version
Router MDSP Configuration Submode

When you issue the router mdsp command, the CLI prompt changes to "config-msdp" indicating that you have entered router MSDP configuration submode.

In the following sample output, the question mark (?) online help function displays all the commands available under router MSDP configuration submode.
RP/0/RP0/CP0:router(config)# router msdp
RP/0/RP0/CP0:router(config-msdp)# ?
  cache-sa-holdtime  Configure Cache SA State holdtime period
  cache-sa-state     Configure this systems SA cache access-lists
  commit             Commit the configuration changes to running
  connect-source     Configure source address used for MSDP connection
  default            Set a command to its defaults
  default-peer       Default MSDP peer to accept SA messages from
  describe           Describe a command without taking real actions
  do                 Run an exec command
  exit               Exit from this submode
  no                 Negate a command or set its defaults
  originator-id      Configure MSDP Originator ID
  peer               MSDP Peer configuration subcommands
  sa-filter          Filter SA messages from peer
  show               Show contents of configuration
  ttl-threshold      Configure TTL Threshold for MSDP Peer
Understanding Interface Configuration Inheritance

The Cisco IOS XR software allows you to configure commands for a large number of interfaces by simply applying command configuration within a multicast routing submode that could be inherited by all interfaces. To override the inheritance mechanism, you can enter interface configuration submode and explicitly enter a different command parameter.

For example, in the following configuration you could quickly specify (under router PIM configuration mode) that all existing and new PIM interfaces on your router will use the hello interval parameter of 420 seconds. However, Packet over SONET interface 0/1/0/1 overrides the global interface configuration and uses the hello interval time of 210 seconds.
RP/0/RP0/CPU0:router(config)# router pim
RP/0/RP0/CPU0:router(config-pim-ipv4)# hello-interval 420
RP/0/RP0/CPU0:router(config-pim-ipv4)# interface pos 0/1/0/1
RP/0/RP0/CPU0:router(config-pim-ipv4-if)# hello-interval 210
The following is a listing of commands (specified under the appropriate router submode) that use the inheritance mechanism:
router pim
  interface all enable
  interface all disable
  dr-priority
  hello-interval
  join-prune-interval
router igmp
  interface all router disable
  interface all router enable
  version
  query-interval
  query-max-response-time
  explicit-tracking
router mld
  interface all disable
  interface all enable
  version
  query-interval
  query-max-response-time
  explicit-tracking
router msdp
  connect-source
  sa-filter
  filter-sa-request list
  remote-as
  ttl-threshold
Understanding Enabling and Disabling Interfaces

When the Cisco IOS XR multicast routing feature is configured on your router, by default, no interfaces are enabled.

To enable multicast routing and protocols on a single interface or multiple interfaces, you must explicitly enable interfaces using the interface command in multicast routing configuration mode.

To set up multicast routing on all interfaces, enter the interface all command in multicast routing configuration mode. For any interface to be fully enabled for multicast routing, it must be enabled specifically (or be default) in multicast routing configuration mode, and it must not be disabled in the PIM and IGMP/MLD configuration modes.

For example, in the following configuration all interfaces are explicitly configured from multicast routing configuration submode:
RP/0/RP0/CPU0:router(config)# multicast-routing
RP/0/RP0/CPU0:router(config-mcast-ipv4)# interface all enable
To disable an interface that was globally configured from the multicast routing configuration submode, you enter interface configuration submode, as illustrated in the following example:
RP/0/RP0/CPU0:router(config-mcast-ipv4)# interface pos 0/1/0/0
RP/0/RP0/CPU0:router(config-mcast-ipv4-if)# disable
How to Implement Multicast on Cisco IOS XR Software

This section contains instructions for the following tasks. The first two tasks are required to configure a basic multicast configuration. The remaining tasks are optional tasks that help you in optimizing, debugging and discovering the routers in your multicast network.

•Configuring PIM-SM and PIM-SSM (required)

•Configuring a Static RP and Allowing Backward Compatibility (required)

•Configuring Auto-RP to Automate Group-to-RP Mappings (optional)

•Configuring the BSR (optional)

•Configuring Multicast Nonstop Forwarding (optional)

•Interconnecting PIM-SM Domains with MSDP (optional)

•Controlling Source Information on MSDP Peer Routers (optional)

•Configuring Multicast Quality of Service (optional)

Configuring PIM-SM and PIM-SSM

PIM is an efficient IP routing protocol that is "independent" of a routing table. Unlike other multicast protocols such as MOSPF or DVMRP.

Cisco IOS XR software supports PIM-SM and PIM-SSM permitting both to operate on your router at the same time.

PIM-SM Operations

PIM in sparse mode operation is used in a multicast network when relatively few routers are involved in each multicast and these routers do not forward multicast packets for a group, unless there is an explicit request for the traffic.

For more information about PIM-SM, see the "PIM-Sparse Mode" section.

PIM-SSM Operations

PIM in Source Specific Multicast operation uses information found on source addresses for a multicast group provided by receivers and performs source filtering on traffic.

•By default, PIM-SSM operates in the 232.0.0.0/8 multicast group range for IPv4 and ff3x::/32 (where x is any valid scope) in IPv6. To configure these values, use the ssm range command.

•If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers must be upgraded with Cisco IOS XR software that supports the SSM feature.

•No MSDP SA messages within the SSM range are accepted, generated, or forwarded.

For more information about PIM-SSM, see the "PIM-Source Specific Multicast" section.

Restrictions

Interoperability with SSM

PIM-SM operations within the SSM range of addresses change to PIM-SSM. In this mode, only PIM (S, G) join and prune messages are generated by the router, and no (S,G) RP shared tree or (*,G) shared tree messages are generated.

IGMP Version

To report multicast memberships to neighboring multicast routers, routers use IGMP and all routers on the subnet must be configured with the same version of IGMP.

A router running Cisco IOS XR software does not automatically detect Version 1 systems. You must use the version command in router IGMP configuration submode to configure the IGMP version.

MLD Version

To report multicast memberships to neighboring multicast routers, routers use MLD and all routers on the subnet must be configured with the same version of MLD.

SUMMARY STEPS

1. configure

2. multicast-routing

3. interface all

4. exit

5. router {igmp | mld}

6. version {1 | 2 | 3}

7. end
or
commit

8. show pim {ipv4 | ipv6} group-map

9. show pim topology

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

multicast-routing
Example:

RP/0/RP0/CPU0:router(config)# multicast-routing

Enters multicast routing configuration mode.

•The following multicast processes are started: MRIB, MFWD, PIM, IGMP and MLD.

•IGMP version 3 is enabled by default.

Step 3

interface all enable
Example:

RP/0/RP0/CPU0:router(config-mcast-ipv4)# interface all

Enables multicast routing and forwarding on all new and existing interfaces.

Step 4

exit
Example:

RP/0/RP0/CPU0:router(config-mcast-ipv4)# exit

Exits multicast routing configuration mode, and returns the router to the parent configuration mode.
Step 5
router {igmp | mld}
Example:
RP/0/RP0/CPU0:router(config)# router igmp 
(Optional) Enters router IGMP or MLD configuration mode.
Step 6

version {1 | 2 | 3}
Example:

RP/0/RP0/CPU0:router(config-igmp)# version 3

(Optional) Selects the IGMP version that the router interface uses.

•The default is version 3.

•Host receivers must support IGMPv3 for PIM-SSM operation.

•If this command is configured in router IGMP configuration mode, parameters are inherited by all new and existing interfaces. You can override these parameters on individual interfaces from interface configuration mode.
Step 7

end
or
commit
Example:

RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or

RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 8

show pim {ipv4 | ipv6} group-map
Example:

RP/0//CPU0:router# show pim ipv4 group-map

(Optional) Displays group-to-PIM mode mapping.

Step 9

show pim topology
Example:

RP/0/RP0/CPU0:router# show pim topology

(Optional) Displays PIM topology table information for a specific group or all groups.
Configuring a Static RP and Allowing Backward Compatibility

When PIM is configured in sparse mode, you must choose one or more routers to operate as a rendezvous point (RP) for a multicast group. An RP is a single common root placed at a chosen point of a shared distribution tree. An RP can either be configured statically in each router, or learned through Auto-RP or BSR.

This task configures a static RP. For more information about RPs, see the "Rendezvous Points" section. For configuration information for Auto-RP, see the "Configuring Auto-RP to Automate Group-to-RP Mappings" section.

SUMMARY STEPS

1. configure

2. router pim [address-family ipv6]

3. rp-address ip-address [group-access-list-number] [bidir] [override]

4. old-register-checksum

5. exit

6. ipv4 access-list name

7. [sequence-number] permit source [source-wildcard]

8. end
or
commit

9. show version

DETAILED STEPS
Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router pim [address-family ipv4]
Example:

RP/0/RP0/CPU0:router(config)# router pim

Enters router PIM configuration mode.

Step 3

rp-address ip-address [group-access-list-number] [bidir] [override]
Example:

RP/0/RP0/CPU0:router(config-pim-ipv4)# rp-address 172.16.6.22 rp-access

Assigns an RP to multicast groups.

•If you specify a group-access-list-number value, you must configure the optional ipv4 access-list command.

Step 4

old-register-checksum
Example:

RP/0/RP0/CPU0:router(config-pim-ipv4)# old-register-checksum

(Optional) Allows backward compatibility on the RP that uses old register checksum methodology.

Step 5

exit
Example:

RP/0/RP0/CPU0:router(config-pim-ipv4)# exit

Exits PIM configuration mode, and returns the router to the parent configuration mode.

Step 6

ipv4 access-list name
Example:

RP/0/RP0/CPU0:router(config)# ipv4 access-list rp-access

(Optional) Enters IPv4 access list configuration mode and configures the RP access list.

•The access list called "rp-access" permits multicast group 239.1.1.1.

Step 7

[sequence-number] permit source [source-wildcard]
Example:

RP/0/RP0/CPU0:router(config-ipv4-acl)# permit 239.1.1.1

(Optional) Permits multicast group 239.1.1.1 for the "rp-access" list.

Tip The commands in Step 6 and Step 7 can be combined in one command string and entered from global configuration mode like this: access-list rp-access permit 239.1.1.1.
Step 8

end
or
commit
Example:

RP/0/RP0/CPU0:router(config-ospf-ar-if)# end
or

RP/0/RP0/CPU0:router(config-ospf-ar-if)# commit
Saves configuration changes.

•When you issue the end command, the system prompts you to commit changes:
Uncommitted changes found, commit them before 
exiting(yes/no/cancel)? 
[cancel]:
–Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

–Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

–Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

•Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.
Step 9

show version
Example:

RP/0/RP0/CPU0:router# show version

Displays the software release version.
Configuring Auto-RP to Automate Group-to-RP Mappings

This task configures the Auto-RP mechanism to automate the distribution of group-to-RP mappings in your network. In a network running Auto-RP, at least one router must operate as an RP candidate and another router must operate as an RP mapping agent.

Note BSR is supported under IPv4 only.

For more information about Auto-RP, see the "Auto-RP" section.

SUMMARY STEPS

1. configure

2. router pim [address-family ipv4]

3. auto-rp candidate-rp interface-type interface-number scope ttl-value [group-list access-list-number] [interval seconds] [bidir]

4. auto-rp mapping-agent interface-type interface-number scope ttl-value [interval seconds]

5. exit

6. ipv4 access-list name [sequence-number] permit source [source-wildcard]

7. end
or
commit

DETAILED STEPS

Command or Action

Purpose

Step 1

configure
Example:

RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

router pim [address-family ipv4]
Example:

RP/0/RP0/CPU0:router(config)# router pim

Enters router PIM configuration mode.

Step 3

auto-rp candidate-rp interface-type interface-number scope ttl-value [group-list access-list-number] [interval seconds] [bidir]
Example:

RP/0/RP0/CPU0:router(config-pim-ipv4)# auto-rp candidate-rp pos 0/1/0/1 scope 31 group-list 2

Configures an RP candidate that sends messages to the CISCO-RP-ANNOUNCE multicast group (224.0.1.39).

•This example sends RP announcements out all PIM-enabled interfaces for a maximum of 31 hops. The IP address by which the router wants to be identified as an RP is the IP address associated with Packet over SONET interface 0/1/0/1.

•Access list 2 designates the groups this router serves as RP.