Software Configuration Guide, Cisco IOS XE Denali 16.1.x (Catalyst 3650 Switches)

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.

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 PIM

Before you begin the PIM configuration process, decide which PIM mode to use. This is based on the applications you intend to support on your network. Use the following guidelines:
- In general, if the application is one-to-many or many-to-many in nature, then PIM-SM can be used successfully.
- For optimal one-to-many application performance, SSM is appropriate but requires IGMP version 3 support.

Before you configure PIM stub routing, check that you have met these conditions:

You must have IP multicast routing configured on both the stub router and the central router. You must also have PIM mode (dense-mode, sparse-mode, or sparse-dense-mode) configured on the uplink interface of the stub router.
You must also configure either Enhanced Interior Gateway Routing Protocol (EIGRP) stub routing or Open Shortest Path First (OSPF) stub routing on the device.

The PIM stub router does not route the transit traffic between the distribution routers. Unicast (EIGRP) stub routing enforces this behavior. You must configure unicast stub routing to assist the PIM stub router behavior.

Note

For information about EIGRP or OSPF configurations, see the Catalyst 3650 Routing Configuration Guide, Release 3SE.

Restrictions for PIM

The following are the restrictions for configuring PIM:

PIM is not supported when running the LAN Base feature set.

PIMv1 and PIMv2 Interoperability

To avoid misconfiguring multicast routing on your device, review the information in this section.

The Cisco PIMv2 implementation provides interoperability and transition between Version 1 and Version 2, although there might be some minor problems.

You can upgrade to PIMv2 incrementally. PIM Versions 1 and 2 can be configured on different routers and multilayer devices within one network. Internally, all routers and multilayer devices on a shared media network must run the same PIM version. Therefore, if a PIMv2 device detects a PIMv1 device, the Version 2 device downgrades itself to Version 1 until all Version 1 devices have been shut down or upgraded.

PIMv2 uses the BSR to discover and announce RP-set information for each group prefix to all the routers and multilayer devices in a PIM domain. PIMv1, together with the Auto-RP feature, can perform the same tasks as the PIMv2 BSR. However, Auto-RP is a standalone protocol, separate from PIMv1, and is a proprietary Cisco protocol. PIMv2 is a standards track protocol in the IETF.

Note

We recommend that you use PIMv2. The BSR function interoperates with Auto-RP on Cisco routers and multilayer devices.

When PIMv2 devices interoperate with PIMv1 devices, Auto-RP should have already been deployed. A PIMv2 BSR that is also an Auto-RP mapping agent automatically advertises the RP elected by Auto-RP. That is, Auto-RP sets its single RP on every router or multilayer device in the group. Not all routers and devices in the domain use the PIMv2 hash function to select multiple RPs.

Dense-mode groups in a mixed PIMv1 and PIMv2 region need no special configuration; they automatically interoperate.

Sparse-mode groups in a mixed PIMv1 and PIMv2 region are possible because the Auto-RP feature in PIMv1 interoperates with the PIMv2 RP feature. Although all PIMv2 devices can also use PIMv1, we recommend that the RPs be upgraded to PIMv2. To ease the transition to PIMv2, we recommend:

Using Auto-RP throughout the region.
Configuring sparse-dense mode throughout the region.

If Auto-RP is not already configured in the PIMv1 regions, configure Auto-RP.

Restrictions for Configuring PIM Stub Routing

The IP services image contains complete multicast routing.
Only directly connected multicast (IGMP) receivers and sources are allowed in the Layer 2 access domains. The PIM protocol is not supported in access domains.
In a network using PIM stub routing, the only allowable route for IP traffic to the user is through a device that is configured with PIM stub routing.
The redundant PIM stub router topology is not supported. Only the nonredundant access router topology is supported by the PIM stub feature.
PIM stub routing is supported when running the IP Base and IP Services feature sets.

Restrictions for Configuring Auto-RP and BSR

Take into consideration your network configuration, and the following restrictions when configuring Auto-RP and BSR:

Restrictions for Configuring Auto-RP

The following are restrictions for configuring Auto-RP (if used in your network configuration):

Auto-RP is not supported when running the LAN Base feature set.
If you configure PIM in sparse mode or sparse-dense mode and do not configure Auto-RP, you must manually configure an RP.
If routed interfaces are configured in sparse mode, Auto-RP can still be used if all devices are configured with a manual RP address for the Auto-RP groups.
If routed interfaces are configured in sparse mode and you enter the ip pim autorp listener global configuration command, Auto-RP can still be used even if all devices are not configured with a manual RP address for the Auto-RP groups.

Restrictions for Configuring BSR

The following are the restrictions for configuring BSR (if used in your network configuration):

Configure the candidate BSRs as the RP-mapping agents for Auto-RP.
For group prefixes advertised through Auto-RP, the PIMv2 BSR mechanism should not advertise a subrange of these group prefixes served by a different set of RPs. In a mixed PIMv1 and PIMv2 domain, have backup RPs serve the same group prefixes. This prevents the PIMv2 DRs from selecting a different RP from those PIMv1 DRs, due to the longest match lookup in the RP-mapping database.

Restrictions and Guidelines for Configuring Auto-RP and BSR

The following are restrictions for configuring Auto-RP and BSR (if used in your network configuration):

If your network is all Cisco routers and multilayer devices, you can use either Auto-RP or BSR.
If you have non-Cisco routers in your network, you must use BSR.

If you have Cisco PIMv1 and PIMv2 routers and multilayer devices and non-Cisco routers, you must use both Auto-RP and BSR. If your network includes routers from other vendors, configure the Auto-RP mapping agent and the BSR on a Cisco PIMv2 device. Ensure that no PIMv1 device is located in the path a between the BSR and a non-Cisco PIMv2 device.

Note

There are two approaches to using PIMv2. You can use Version 2 exclusively in your network or migrate to Version 2 by employing a mixed PIM version environment.

Because bootstrap messages are sent hop-by-hop, a PIMv1 device prevents these messages from reaching all routers and multilayer devices in your network. Therefore, if your network has a PIMv1 device in it and only Cisco routers and multilayer devices, it is best to use Auto-RP.
If you have a network that includes non-Cisco routers, configure the Auto-RP mapping agent and the BSR on a Cisco PIMv2 router or multilayer device. Ensure that no PIMv1 device is on the path between the BSR and a non-Cisco PIMv2 router.
If you have non-Cisco PIMv2 routers that need to interoperate with Cisco PIMv1 routers and multilayer devices, both Auto-RP and a BSR are required. We recommend that a Cisco PIMv2 device be both the Auto-RP mapping agent and the BSR.

Restrictions for Auto-RP Enhancement

The simultaneous deployment of Auto-RP and bootstrap router (BSR) is not supported.

Protocol Independent Multicast Overview

The Protocol Independent Multicast (PIM) protocol maintains the current IP multicast service mode of receiver-initiated membership. PIM is not dependent on a specific unicast routing protocol; it is IP routing protocol independent and can leverage whichever unicast routing protocols are used to populate the unicast routing table, including Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), and static routes. PIM uses unicast routing information to perform the multicast forwarding function.

Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the reverse path forwarding (RPF) check function instead of building up a completely independent multicast routing table. Unlike other routing protocols, PIM does not send and receive routing updates between routers.

PIM is defined in RFC 4601, Protocol Independent Multicast - Sparse Mode (PIM-SM)

PIM can operate in dense mode or sparse mode. The router can also handle both sparse groups and dense groups at the same time (sparse-dense mode). The mode determines how the router populates its multicast routing table and how the router forwards multicast packets it receives from its directly connected LANs.

For information about PIM forwarding (interface) modes, see the following sections:

PIM Dense Mode

PIM dense mode (PIM-DM) uses a push model to flood multicast traffic to every corner of the network. This push model is a method for delivering data to the receivers without the receivers requesting the data. This method is efficient in certain deployments in which there are active receivers on every subnet in the network.

In dense mode, a router assumes that all other routers want to forward multicast packets for a group. If a router receives a multicast packet and has no directly connected members or PIM neighbors present, a prune message is sent back to the source. Subsequent multicast packets are not flooded to this router on this pruned branch. PIM builds source-based multicast distribution trees.

PIM-DM initially floods multicast traffic throughout the network. Routers that have no downstream neighbors prune back the unwanted traffic. This process repeats every 3 minutes.

Routers accumulate state information by receiving data streams through the flood and prune mechanism. These data streams contain the source and group information so that downstream routers can build up their multicast forwarding table. PIM-DM supports only source trees--that is, (S,G) entries--and cannot be used to build a shared distribution tree.

Note

Dense mode is not often used and its use is not recommended. For this reason it is not specified in the configuration tasks in related modules.

PIM Sparse Mode

PIM sparse mode (PIM-SM) uses a pull model to deliver multicast traffic. Only network segments with active receivers that have explicitly requested the data will receive the traffic.

Unlike dense mode interfaces, sparse mode interfaces are added to the multicast routing table only when periodic Join messages are received from downstream routers, or when a directly connected member is on the interface. When forwarding from a LAN, sparse mode operation occurs if an RP is known for the group. If so, the packets are encapsulated and sent toward the RP. When no RP is known, the packet is flooded in a dense mode fashion. If the multicast traffic from a specific source is sufficient, the first hop router of the receiver may send Join messages toward the source to build a source-based distribution tree.

PIM-SM distributes information about active sources by forwarding data packets on the shared tree. Because PIM-SM uses shared trees (at least, initially), it requires the use of a rendezvous point (RP). The RP must be administratively configured in the network. See the Rendezvous Points section for more information.

In sparse mode, a router assumes that other routers do not want to forward multicast packets for a group, unless there is an explicit request for the traffic. When hosts join a multicast group, the directly connected routers send PIM Join messages toward the RP. The RP keeps track of multicast groups. Hosts that send multicast packets are registered with the RP by the first hop router of that host. The RP then sends Join messages toward the source. At this point, packets are forwarded on a shared distribution tree. If the multicast traffic from a specific source is sufficient, the first hop router of the host may send Join messages toward the source to build a source-based distribution tree.

Sources register with the RP and then data is forwarded down the shared tree to the receivers. The edge routers learn about a particular source when they receive data packets on the shared tree from that source through the RP. The edge router then sends PIM (S,G) Join messages toward that source. Each router along the reverse path compares the unicast routing metric of the RP address to the metric of the source address. If the metric for the source address is better, it will forward a PIM (S,G) Join message toward the source. If the metric for the RP is the same or better, then the PIM (S,G) Join message will be sent in the same direction as the RP. In this case, the shared tree and the source tree would be considered congruent.

If the shared tree is not an optimal path between the source and the receiver, the routers dynamically create a source tree and stop traffic from flowing down the shared tree. This behavior is the default behavior in software. Network administrators can force traffic to stay on the shared tree by using the ip pim spt-threshold infinity command.

PIM-SM scales well to a network of any size, including those with WAN links. The explicit join mechanism prevents unwanted traffic from flooding the WAN links.

Multicast Source Discovery Protocol (MSDP)

Multicast Source Discovery Protocol (MSDP) is used for inter-domain source discovery when PIM SM is used. Each PIM administrative domain has its own RP. In order for the RP in one domain to signal new sources to the RP in the other domain, MSDP is used.

When RP in a domain receives a PIM register message for a new source, with MSDP configured it sends a new source-active (SA) message to all its MSDP peers in other domains. Each intermediate MSDP peer floods this SA message away from the originating RP. The MSDP peers install this SA message in their MSDP sa-cache. If the RPs in other domains have any join requests for the group in the SA message (indicated by the presence of a (*,G) entry with non empty outgoing interface list), the domain is interested in the group, and the RP triggers an (S,G) join toward the source.

Sparse-Dense Mode

If you configure either sparse mode or dense mode on an interface, then sparseness or denseness is applied to the interface as a whole. However, some environments might require PIM to run in a single region in sparse mode for some groups and in dense mode for other groups.

An alternative to enabling only dense mode or only sparse mode is to enable sparse-dense mode. In this case, the interface is treated as dense mode if the group is in dense mode; the interface is treated in sparse mode if the group is in sparse mode. You must have an RP if the interface is in sparse-dense mode and you want to treat the group as a sparse group.

If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the groups for which the router is a member.

Another benefit of sparse-dense mode is that Auto-RP information can be distributed in a dense mode; yet, multicast groups for user groups can be used in a sparse mode manner. Therefore there is no need to configure a default RP at the leaf routers.

When an interface is treated in dense mode, it is populated in the outgoing interface list of a multicast routing table when either of the following conditions is true:

Members or DVMRP neighbors are on the interface.
There are PIM neighbors and the group has not been pruned.

When an interface is treated in sparse mode, it is populated in the outgoing interface list of a multicast routing table when either of the following conditions is true:

Members or DVMRP neighbors are on the interface.
An explicit Join message has been received by a PIM neighbor on the interface.

PIM Versions

PIMv2 includes these improvements over PIMv1:

A single, active rendezvous point (RP) exists per multicast group, with multiple backup RPs. This single RP compares to multiple active RPs for the same group in PIMv1.
A bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution function that enables routers and multilayer devices to dynamically learn the group-to-RP mappings.

Sparse mode and dense mode are properties of a group, as opposed to an interface.

Note

We strongly recommend using sparse-dense mode as opposed to either sparse mode or dense mode only.

PIM join and prune messages have more flexible encoding for multiple address families.
A more flexible hello packet format replaces the query packet to encode current and future capability options.
Register messages sent to an RP specify whether they are sent by a border router or a designated router.
PIM packets are no longer inside IGMP packets; they are standalone packets.

PIM Stub Routing

The PIM stub routing feature, available in all of the device software images, reduces resource usage by moving routed traffic closer to the end user.

The PIM stub routing feature supports multicast routing between the distribution layer and the access layer. It supports two types of PIM interfaces, uplink PIM interfaces, and PIM passive interfaces. A routed interface configured with the PIM passive mode does not pass or forward PIM control traffic, it only passes and forwards IGMP traffic.

In a network using PIM stub routing, the only allowable route for IP traffic to the user is through a device that is configured with PIM stub routing. PIM passive interfaces are connected to Layer 2 access domains, such as VLANs, or to interfaces that are connected to other Layer 2 devices. Only directly connected multicast (IGMP) receivers and sources are allowed in the Layer 2 access domains. The PIM passive interfaces do not send or process any received PIM control packets.

When using PIM stub routing, you should configure the distribution and remote routers to use IP multicast routing and configure only the device as a PIM stub router. The device does not route transit traffic between distribution routers. You also need to configure a routed uplink port on the device. The device uplink port cannot be used with SVIs. If you need PIM for an SVI uplink port, you should upgrade to the IP Services feature set.

Note

You must also configure EIGRP stub routing when configuring PIM stub routing on the device

The redundant PIM stub router topology is not supported. The redundant topology exists when there is more than one PIM router forwarding multicast traffic to a single access domain. PIM messages are blocked, and the PIM asset and designated router election mechanisms are not supported on the PIM passive interfaces. Only the nonredundant access router topology is supported by the PIM stub feature. By using a nonredundant topology, the PIM passive interface assumes that it is the only interface and designated router on that access domain.

Figure 1. PIM Stub Router Configuration. In the following figure, the Device A routed uplink port 25 is connected to the router and PIM stub routing is enabled on the VLAN 100 interfaces and on Host 3. This configuration allows the directly connected hosts to receive traffic from multicast source 200.1.1.3.

IGMP Helper

PIM stub routing moves routed traffic closer to the end user and reduces network traffic. You can also reduce traffic by configuring a stub router (switch) with the IGMP helper feature.

You can configure a stub router (switch) with the ip igmp helper-address ip-address interface configuration command to enable the switch to send reports to the next-hop interface. Hosts that are not directly connected to a downstream router can then join a multicast group sourced from an upstream network. The IGMP packets from a host wanting to join a multicast stream are forwarded upstream to the next-hop device when this feature is configured. When the upstream central router receives the helper IGMP reports or leaves, it adds or removes the interfaces from its outgoing interface list for that group.

Rendezvous Points

A rendezvous point (RP) is a role that a device performs when operating in Protocol Independent Multicast (PIM) Sparse Mode (SM). An RP is required only in networks running PIM SM. In the PIM-SM model, only network segments with active receivers that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data is in contrast to PIM Dense Mode (PIM DM). In PIM DM, multicast traffic is initially flooded to all segments of the network. Routers that have no downstream neighbors or directly connected receivers prune back the unwanted traffic.

An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network, sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared distribution tree. By default, when the first hop device of the receiver learns about the source, it will send a Join message directly to the source, creating a source-based distribution tree from the source to the receiver. This source tree does not include the RP unless the RP is located within the shortest path between the source and receiver.

In most cases, the placement of the RP in the network is not a complex decision. By default, the RP is needed only to start new sessions with sources and receivers. Consequently, the RP experiences little overhead from traffic flow or processing. In PIM version 2, the RP performs less processing than in PIM version 1 because sources must only periodically register with the RP to create state.

Auto-RP

In the first version of PIM-SM, all leaf routers (routers directly connected to sources or receivers) were required to be manually configured with the IP address of the RP. This type of configuration is also known as static RP configuration. Configuring static RPs is relatively easy in a small network, but it can be laborious in a large, complex network.

Following the introduction of PIM-SM version 1, Cisco implemented a version of PIM-SM with the Auto-RP feature. Auto-RP automates the distribution of group-to-RP mappings in a PIM network. Auto-RP has the following benefits:

Configuring the use of multiple RPs within a network to serve different groups is easy.
Auto-RP allows load splitting among different RPs and arrangement of RPs according to the location of group participants.
Auto-RP avoids inconsistent, manual RP configurations that can cause connectivity problems.

Multiple RPs can be used to serve different group ranges or serve as backups to each other. For Auto-RP to work, a router must be designated as an RP-mapping agent, which receives the RP-announcement messages from the RPs and arbitrates conflicts. The RP-mapping agent then sends the consistent group-to-RP mappings to all other routers. Thus, all routers automatically discover which RP to use for the groups they support.

Note

If you configure PIM in sparse mode or sparse-dense mode and do not configure Auto-RP, you must statically configure an RP.

Note

If 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.

To make Auto-RP work, a router must be designated as an RP mapping agent, which receives the RP announcement messages from the RPs and arbitrates conflicts. The RP mapping agent then sends the consistent group-to-RP mappings to all other routers by dense mode flooding. Thus, all routers automatically discover which RP to use for the groups they support. The Internet Assigned Numbers Authority (IANA) has assigned two group addresses, 224.0.1.39 and 224.0.1.40, for Auto-RP. One advantage of Auto-RP is that any change to the RP designation must be configured only on the routers that are RPs and not on the leaf routers. Another advantage of Auto-RP is that it offers the ability to scope the RP address within a domain. Scoping can be achieved by defining the time-to-live (TTL) value allowed for the Auto-RP advertisements.

Each method for configuring an RP has its own strengths, weaknesses, and level of complexity. In conventional IP multicast network scenarios, we recommend using Auto-RP to configure RPs because it is easy to configure, well-tested, and stable. The alternative ways to configure an RP are static RP, Auto-RP, and bootstrap router.

The Role of Auto-RP in a PIM Network

Auto-RP automates the distribution of group-to-rendezvous point (RP) mappings in a PIM network. To make Auto-RP work, a device must be designated as an RP mapping agent, which receives the RP announcement messages from the RPs and arbitrates conflicts. The RP mapping agent then sends the consistent group-to-RP mappings to all other devices by way of dense mode flooding.

Thus, all routers automatically discover which RP to use for the groups they support. The Internet Assigned Numbers Authority (IANA) has assigned two group addresses, 224.0.1.39 and 224.0.1.40, for Auto-RP.

The mapping agent receives announcements of intention to become the RP from Candidate-RPs. The mapping agent then announces the winner of the RP election. This announcement is made independently of the decisions by the other mapping agents.

Multicast Boundaries

Administratively-scoped boundaries can be used to limit the forwarding of multicast traffic outside of a domain or subdomain. This approach uses a special range of multicast addresses, called administratively-scoped addresses, as the boundary mechanism. If you configure an administratively-scoped boundary on a routed interface, multicast traffic whose multicast group addresses fall in this range cannot enter or exit this interface, which provides a firewall for multicast traffic in this address range.

Note

Multicast boundaries and TTL thresholds control the scoping of multicast domains; however, TTL thresholds are not supported by the device. You should use multicast boundaries instead of TTL thresholds to limit the forwarding of multicast traffic outside of a domain or a subdomain.

Figure 2. Administratively-Scoped Boundaries. The following figure shows that Company XYZ has an administratively-scoped boundary set for the multicast address range 239.0.0.0/8 on all routed interfaces at the perimeter of its network. This boundary prevents any multicast traffic in the range 239.0.0.0 through 239.255.255.255 from entering or leaving the network. Similarly, the engineering and marketing departments have an administratively-scoped boundary of 239.128.0.0/16 around the perimeter of their networks. This boundary prevents multicast traffic in the range of 239.128.0.0 through 239.128.255.255 from entering or leaving their respective networks.

You can define an administratively-scoped boundary on a routed interface for multicast group addresses. A standard access list defines the range of addresses affected. When a boundary is defined, no multicast data packets are allowed to flow across the boundary from either direction. The boundary allows the same multicast group address to be reused in different administrative domains.

The IANA has designated the multicast address range 239.0.0.0 to 239.255.255.255 as the administratively-scoped addresses. This range of addresses can then be reused in domains administered by different organizations. The addresses would be considered local, not globally unique.

You can configure the filter-autorp keyword to examine and filter Auto-RP discovery and announcement messages at the administratively scoped boundary. Any Auto-RP group range announcements from the Auto-RP packets that are denied by the boundary access control list (ACL) are removed. An Auto-RP group range announcement is permitted and passed by the boundary only if all addresses in the Auto-RP group range are permitted by the boundary ACL. If any address is not permitted, the entire group range is filtered and removed from the Auto-RP message before the Auto-RP message is forwarded.

Sparse-Dense Mode for Auto-RP

A prerequisite of Auto-RP is that all interfaces must be configured in sparse-dense mode using the ip pim sparse-dense-mode interface configuration command. An interface configured in sparse-dense mode is treated in either sparse mode or dense mode of operation, depending on which mode the multicast group operates. If a multicast group has a known RP, the interface is treated in sparse mode. If a group has no known RP, by default the interface is treated in dense mode and data will be flooded over this interface. (You can prevent dense-mode fallback; see the module “Configuring Basic IP Multicast.”)

To successfully implement Auto-RP and prevent any groups other than 224.0.1.39 and 224.0.1.40 from operating in dense mode, we recommend configuring a “sink RP” (also known as “RP of last resort”). A sink RP is a statically configured RP that may or may not actually exist in the network. Configuring a sink RP does not interfere with Auto-RP operation because, by default, Auto-RP messages supersede static RP configurations. We recommend configuring a sink RP for all possible multicast groups in your network, because it is possible for an unknown or unexpected source to become active. If no RP is configured to limit source registration, the group may revert to dense mode operation and be flooded with data.

Auto-RP Benefits

Auto-RP uses IP multicast to automate the distribution of group-to-RP mappings to all Cisco routers and multilayer devices in a PIM network. Auto-RP has these benefits:

Easy to use multiple RPs within a network to serve different group ranges.
Provides load splitting among different RPs and arrangement of RPs according to the location of group participants.
Avoids inconsistent, manual RP configurations on every router and multilayer device in a PIM network, which can cause connectivity problems.

Benefits of Auto-RP in a PIM Network

Auto-RP allows any change to the RP designation to be configured only on the devices that are RPs, not on the leaf routers.
Auto-RP offers the ability to scope the RP address within a domain.

PIMv2 Bootstrap Router

PIMv2 Bootstrap Router (BSR) is another method to distribute group-to-RP mapping information to all PIM routers and multilayer devices in the network. It eliminates the need to manually configure RP information in every router and device in the network. However, instead of using IP multicast to distribute group-to-RP mapping information, BSR uses hop-by-hop flooding of special BSR messages to distribute the mapping information.

The BSR is elected from a set of candidate routers and devices in the domain that have been configured to function as BSRs. The election mechanism is similar to the root-bridge election mechanism used in bridged LANs. The BSR election is based on the BSR priority of the device contained in the BSR messages that are sent hop-by-hop through the network. Each BSR device examines the message and forwards out all interfaces only the message that has either a higher BSR priority than its BSR priority or the same BSR priority, but with a higher BSR IP address. Using this method, the BSR is elected.

The elected BSR sends BSR messages with a TTL of 1. Neighboring PIMv2 routers or multilayer devices receive the BSR message and multicast it out all other interfaces (except the one on which it was received) with a TTL of 1. In this way, BSR messages travel hop-by-hop throughout the PIM domain. Because BSR messages contain the IP address of the current BSR, the flooding mechanism enables candidate RPs to automatically learn which device is the elected BSR.

Candidate RPs send candidate RP advertisements showing the group range for which they are responsible to the BSR, which stores this information in its local candidate-RP cache. The BSR periodically advertises the contents of this cache in BSR messages to all other PIM devices in the domain. These messages travel hop-by-hop through the network to all routers and devices, which store the RP information in the BSR message in their local RP cache. The routers and devices select the same RP for a given group because they all use a common RP hashing algorithm.

PIM Domain Border

As IP multicast becomes more widespread, the chance of one PIMv2 domain bordering another PIMv2 domain increases. Because two domains probably do not share the same set of RPs, BSR, candidate RPs, and candidate BSRs, you need to constrain PIMv2 BSR messages from flowing into or out of the domain. Allowing messages to leak across the domain borders could adversely affect the normal BSR election mechanism and elect a single BSR across all bordering domains and comingle candidate RP advertisements, resulting in the election of RPs in the wrong domain.

Multicast Forwarding

Forwarding of multicast traffic is accomplished by multicast-capable routers. These routers create distribution trees that control the path that IP multicast traffic takes through the network in order to deliver traffic to all receivers.

Multicast traffic flows from the source to the multicast group over a distribution tree that connects all of the sources to all of the receivers in the group. This tree may be shared by all sources (a shared tree) or a separate distribution tree can be built for each source (a source tree). The shared tree may be one-way or bidirectional.

Before describing the structure of source and shared trees, it is helpful to explain the notations that are used in multicast routing tables. These notations include the following:

(S,G) = (unicast source for the multicast group G, multicast group G)
(*,G) = (any source for the multicast group G, multicast group G)

The notation of (S,G), pronounced “S comma G,” enumerates a shortest path tree where S is the IP address of the source and G is the multicast group address.

Shared trees are (*,G) and the source trees are (S,G) and always routed at the sources.

Multicast Distribution Source Tree

The simplest form of a multicast distribution tree is a source tree. A source tree has its root at the source host and has branches forming a spanning tree through the network to the receivers. Because this tree uses the shortest path through the network, it is also referred to as a shortest path tree (SPT).

The figure shows an example of an SPT for group 224.1.1.1 rooted at the source, Host A, and connecting two receivers, Hosts B and C.

Using standard notation, the SPT for the example shown in the figure would be (192.168.1.1, 224.1.1.1).

The (S,G) notation implies that a separate SPT exists for each individual source sending to each group--which is correct.

Multicast Distribution Shared Tree

Unlike source trees that have their root at the source, shared trees use a single common root placed at some chosen point in the network. This shared root is called a rendezvous point (RP).

The following figure shows a shared tree for the group 224.2.2.2 with the root located at Router D. This shared tree is unidirectional. Source traffic is sent towards the RP on a source tree. The traffic is then forwarded down the shared tree from the RP to reach all of the receivers (unless the receiver is located between the source and the RP, in which case it will be serviced directly).

In this example, multicast traffic from the sources, Hosts A and D, travels to the root (Router D) and then down the shared tree to the two receivers, Hosts B and C. Because all sources in the multicast group use a common shared tree, a wildcard notation written as (*, G), pronounced “star comma G,” represents the tree. In this case, * means all sources, and G represents the multicast group. Therefore, the shared tree shown in the figure would be written as (*, 224.2.2.2).

Both source trees and shared trees are loop-free. Messages are replicated only where the tree branches. Members of multicast groups can join or leave at any time; therefore the distribution trees must be dynamically updated. When all the active receivers on a particular branch stop requesting the traffic for a particular multicast group, the routers prune that branch from the distribution tree and stop forwarding traffic down that branch. If one receiver on that branch becomes active and requests the multicast traffic, the router will dynamically modify the distribution tree and start forwarding traffic again.

Source Tree Advantage

Source trees have the advantage of creating the optimal path between the source and the receivers. This advantage guarantees the minimum amount of network latency for forwarding multicast traffic. However, this optimization comes at a cost. The routers must maintain path information for each source. In a network that has thousands of sources and thousands of groups, this overhead can quickly become a resource issue on the routers. Memory consumption from the size of the multicast routing table is a factor that network designers must take into consideration.

Shared Tree Advantage

Shared trees have the advantage of requiring the minimum amount of state in each router. This advantage lowers the overall memory requirements for a network that only allows shared trees. The disadvantage of shared trees is that under certain circumstances the paths between the source and receivers might not be the optimal paths, which might introduce some latency in packet delivery. For example, in the figure above the shortest path between Host A (source 1) and Host B (a receiver) would be Router A and Router C. Because we are using Router D as the root for a shared tree, the traffic must traverse Routers A, B, D and then C. Network designers must carefully consider the placement of the rendezvous point (RP) when implementing a shared tree-only environment.

In unicast routing, traffic is routed through the network along a single path from the source to the destination host. A unicast router does not consider the source address; it considers only the destination address and how to forward the traffic toward that destination. The router scans through its routing table for the destination address and then forwards a single copy of the unicast packet out the correct interface in the direction of the destination.

In multicast forwarding, the source is sending traffic to an arbitrary group of hosts that are represented by a multicast group address. The multicast router must determine which direction is the upstream direction (toward the source) and which one is the downstream direction (or directions) toward the receivers. If there are multiple downstream paths, the router replicates the packet and forwards it down the appropriate downstream paths (best unicast route metric)--which is not necessarily all paths. Forwarding multicast traffic away from the source, rather than to the receiver, is called Reverse Path Forwarding (RPF). RPF is described in the following section.

PIM Shared Tree and Source Tree

By default, members of a group receive data from senders to the group across a single data-distribution tree rooted at the RP.

Figure 4. Shared Tree and Source Tree (Shortest-Path Tree). The following figure shows this type of shared-distribution tree. Data from senders is delivered to the RP for distribution to group members joined to the shared tree.

If the data rate warrants, leaf routers (routers without any downstream connections) on the shared tree can use 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 software devices to a source tree upon receiving the first data packet from a source.

This process describes the move from a shared tree to a source tree:

A receiver joins a group; leaf Router C sends a join message toward the RP.
The RP puts a link to Router C in its outgoing interface list.
A source sends data; Router A encapsulates the data in a register message and sends it to the RP.
The RP forwards the data down the shared tree to Router C and sends a join message toward the source. At this point, data might arrive twice at Router C, once encapsulated and once natively.
When data arrives natively (unencapsulated) at the RP, it sends a register-stop message to Router A.
By default, reception of the first data packet prompts Router C to send a join message toward the source.
When Router C receives data on (S, G), it sends a prune message for the source up the shared tree.
The RP deletes the link to Router C from the outgoing interface of (S, G). The RP triggers a prune message toward the source.

Join and prune messages are sent for sources and RPs. They are sent hop-by-hop and are processed by each PIM device 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.

Multiple sources sending to groups use the shared tree. You can configure the PIM device to stay on the shared tree.

The change from shared to source tree happens when the first data packet arrives at the last-hop router. This change depends upon the threshold that is configured by using the ip pim spt-threshold global configuration command.

The shortest-path tree requires more memory than the shared tree but reduces delay. You may want to postpone its use. Instead of allowing the leaf router to immediately move to the shortest-path tree, you can specify that the traffic must first reach a threshold.

You can configure when a PIM leaf router should join the shortest-path tree for a specified group. If a source sends at a rate greater than or equal to the specified kbps rate, the multilayer switch triggers a PIM join message toward the source to construct a source tree (shortest-path tree). If the traffic rate from the source drops below the threshold value, the leaf router switches back to the shared tree and sends a prune message toward the source.

You can specify to which groups the shortest-path tree threshold applies by using a group list (a standard access list). If a value of 0 is specified or if the group list is not used, the threshold applies to all groups.

Reverse Path Forwarding

In unicast routing, traffic is routed through the network along a single path from the source to the destination host. A unicast router does not consider the source address; it considers only the destination address and how to forward the traffic toward that destination. The router scans through its routing table for the destination network and then forwards a single copy of the unicast packet out the correct interface in the direction of the destination.

In multicast forwarding, the source is sending traffic to an arbitrary group of hosts that are represented by a multicast group address. The multicast router must determine which direction is the upstream direction (toward the source) and which one is the downstream direction (or directions) toward the receivers. If there are multiple downstream paths, the router replicates the packet and forwards it down the appropriate downstream paths (best unicast route metric)--which is not necessarily all paths. Forwarding multicast traffic away from the source, rather than to the receiver, is called Reverse Path Forwarding (RPF). RPF is an algorithm used for forwarding multicast datagrams.

Protocol Independent Multicast (PIM) uses the unicast routing information to create a distribution tree along the reverse path from the receivers towards the source. The multicast routers then forward packets along the distribution tree from the source to the receivers. RPF is a key concept in multicast forwarding. It enables routers to correctly forward multicast traffic down the distribution tree. RPF makes use of the existing unicast routing table to determine the upstream and downstream neighbors. A router will forward a multicast packet only if it is received on the upstream interface. This RPF check helps to guarantee that the distribution tree will be loop-free.

RPF Check

When a multicast packet arrives at a router, the router performs an RPF check on the packet. If the RPF check succeeds, the packet is forwarded. Otherwise, it is dropped.

For traffic flowing down a source tree, the RPF check procedure works as follows:

The router looks up the source address in the unicast routing table to determine if the packet has arrived on the interface that is on the reverse path back to the source.
If the packet has arrived on the interface leading back to the source, the RPF check succeeds and the packet is forwarded out the interfaces present in the outgoing interface list of a multicast routing table entry.
If the RPF check in Step 2 fails, the packet is dropped.

The figure shows an example of an unsuccessful RPF check.

As the figure illustrates, a multicast packet from source 151.10.3.21 is received on serial interface 0 (S0). A check of the unicast route table shows that S1 is the interface this router would use to forward unicast data to 151.10.3.21. Because the packet has arrived on interface S0, the packet is discarded.

The figure shows an example of a successful RPF check.

In this example, the multicast packet has arrived on interface S1. The router refers to the unicast routing table and finds that S1 is the correct interface. The RPF check passes, and the packet is forwarded.

PIM uses both source trees and RP-rooted shared trees to forward datagrams. The RPF check is performed differently for each:

If a PIM router or multilayer device has a source-tree state (that is, an (S, G) entry is present in the multicast routing table), it performs the RPF check against the IP address of the source of the multicast packet.
If a PIM router or multilayer device has a shared-tree state (and no explicit source-tree state), it performs the RPF check on the RP address (which is known when members join the group).

DVMRP and dense-mode PIM use only source trees and use RPF.

Note

DVMRP is not supported on the device.

Sparse-mode PIM uses the RPF lookup function to decide 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.

Default PIM Routing Configuration

This table displays the default PIM routing configuration for the device.

Table 1. Default Multicast Routing Configuration
Feature	Default Setting
Multicast routing	Disabled on all interfaces.
PIM version	Version 2.
PIM mode	No mode is defined.
PIM stub routing	None configured.
PIM RP address	None configured.
PIM domain border	Disabled.
PIM multicast boundary	None.
Candidate BSRs	Disabled.
Candidate RPs	Disabled.
Shortest-path tree threshold rate	0 kb/s.
PIM router query message interval	30 seconds.

Enabling PIM Stub Routing (CLI)

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
interface interface-id
ip pim passive
end
show ip pim interface
show ip igmp groups detail
show ip mroute
show running-config
copy running-config startup-config

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 the global configuration mode.
Step 3	interface `interface-id` Example: `Device(config)# interface gigabitethernet 1/0/1`	Specifies the interface on which you want to enable PIM stub routing, and enters interface configuration mode.
Step 4	ip pim passive Example: `Device(config-if)# ip pim passive`	Configures the PIM stub feature on the interface.
Step 5	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 6	show ip pim interface Example: `Device# show ip pim interface`	(Optional) Displays the PIM stub that is enabled on each interface.
Step 7	show ip igmp groups detail Example: `Device# show ip igmp groups detail`	(Optional) Displays the interested clients that have joined the specific multicast source group.
Step 8	show ip mroute Example: `Device# show ip mroute`	(Optional) Displays the IP multicast routing table.
Step 9	show running-config Example: `Device# show running-config`	Verifies your entries.
Step 10	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Configuring a Rendezvous Point

You must have a rendezvous point (RP), if the interface is in sparse-dense mode and if you want to handle the group as a sparse group. You can use these methods:

By manually assigning an RP to multicast groups.
As a standalone, Cisco-proprietary protocol separate from PIMv1, which includes:
- Setting up Auto-RP in a new internetwork
- Adding Auto-RP to an existing sparse-mode cloud
- Preventing join messages to false RPs
- Filtering incoming RP announcement messages
By using a standards track protocol in the Internet Engineering Task Force (IETF), which includes configuring PIMv2 BSR .

Note

You can use Auto-RP, BSR, or a combination of both, depending on the PIM version that you are running and the types of routers in your network. For information about working with different PIM versions in your network, see PIMv1 and PIMv2 Interoperability.

Manually Assigning an RP to Multicast Groups (CLI)

If the rendezvous point (RP) for a group is learned through a dynamic mechanism (such as Auto-RP or BSR), you need not perform this task for that RP.

Senders of multicast traffic announce their existence through register messages received from the source first-hop router (designated router) and forwarded to the RP. Receivers of multicast packets use RPs to join a multicast group by using explicit join messages.

Note

RPs are not members of the multicast group; they serve as a meeting place for multicast sources and group members.

You can configure a single RP for multiple groups defined by an access list. If there is no RP configured for a group, the multilayer device responds to the group as dense and uses the dense-mode PIM techniques.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
ip pim rp-address ip-address [access-list-number] [override]
access-list access-list-number {deny | permit} source [source-wildcard]
end
show running-config
copy running-config startup-config

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 the global configuration mode.

Step 3

ip pim rp-address ip-address [access-list-number] [override]

Example:


Device(config)# ip pim rp-address 
10.1.1.1 20 override

Configures the address of a PIM RP.

By default, no PIM RP address is configured. You must configure the IP address of RPs on all routers and multilayer devices (including the RP).

Note

If there is no RP configured for a group, the device treats the group as dense, using the dense-mode PIM techniques.

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

For ip-address , enter the unicast address of the RP in dotted-decimal notation.
(Optional) For access-list-number , enter an IP standard access list number from 1 to 99. If no access list is configured, the RP is used for all groups.
(Optional) The override keyword indicates that if there is a conflict between the RP configured with this command and one learned by Auto-RP or BSR, the RP configured with this command prevails.

Step 4

access-list access-list-number {deny | permit} source [source-wildcard]

Example:


Device(config)# access-list 25 
permit 10.5.0.1 255.224.0.0

Creates a standard access list, repeating the command as many times as necessary.

For access-list-number , enter the access list number specified in Step 2.
The deny keyword denies access if the conditions are matched.
The permit keyword permits access if the conditions are matched.
For source , enter the multicast group address for which the RP should be used.
(Optional) For source-wildcard , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore.

The access list is always terminated by an implicit deny statement for everything.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Setting Up Auto-RP in a New Internetwork (CLI)

If you are setting up Auto-RP in a new internetwork, you do not need a default RP because you configure all the interfaces for sparse-dense mode.

Note

Omit Step 3 in the following procedure, if you want to configure a PIM router as the RP for the local group.

SUMMARY STEPS

enable
show running-config
configure terminal
ip pim send-rp-announce interface-id scope ttl group-list access-list-number interval seconds
access-list access-list-number {deny | permit} source [source-wildcard]
ip pim send-rp-discovery scope ttl
end
show running-config
show ip pim rp mapping
show ip pim rp
copy running-config startup-config

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

show running-config

Example:


Device# show running-config

Verifies that a default RP is already configured on all PIM devices and the RP in the sparse-mode network. It was previously configured with the ip pim rp-address global configuration command.

Note

This step is not required for spare-dense-mode environments.

The selected RP should have good connectivity and be available across the network. Use this RP for the global groups (for example, 224.x.x.x and other global groups). Do not reconfigure the group address range that this RP serves. RPs dynamically discovered through Auto-RP take precedence over statically configured RPs. Assume that it is desirable to use a second RP for the local groups.

Step 3

configure terminal

Example:


Device# configure terminal

Enters the global configuration mode.

Step 4

ip pim send-rp-announce interface-id scope ttl group-list access-list-number interval seconds

Example:


Device(config)# ip pim send-rp-announce gigabitethernet 
1/0/5 scope 20 group-list 10 interval 120

Configures another PIM device to be the candidate RP for local groups.

For interface-id , enter the interface type and number that identifies the RP address. Valid interfaces include physical ports, port channels, and VLANs.
For scope ttl , specify the time-to-live value in hops. Enter a hop count that is high enough so that the RP-announce messages reach all mapping agents in the network. There is no default setting. The range is 1 to 255.
For group-list access-list-number , enter an IP standard access list number from 1 to 99. If no access list is configured, the RP is used for all groups.
For interval seconds , specify how often the announcement messages must be sent. The default is 60 seconds. The range is 1 to 16383.

Step 5

access-list access-list-number {deny | permit} source [source-wildcard]

Example:


Device(config)# access-list 10 permit 10.10.0.0

Creates a standard access list, repeating the command as many times as necessary.

For access-list-number , enter the access list number specified in Step 3.
The deny keyword denies access if the conditions are matched.
The permit keyword permits access if the conditions are matched.
For source , enter the multicast group address range for which the RP should be used.
(Optional) For source-wildcard , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore.

Note

Recall that the access list is always terminated by an implicit deny statement for everything.

Step 6

ip pim send-rp-discovery scope ttl

Example:


Device(config)# ip pim send-rp-discovery scope 50

Finds a device whose connectivity is not likely to be interrupted, and assign it the role of RP-mapping agent.

For scope ttl , specify the time-to-live value in hops to limit the RP discovery packets. All devices within the hop count from the source device receive the Auto-RP discovery messages. These messages tell other devices which group-to-RP mapping to use to avoid conflicts (such as overlapping group-to-RP ranges). There is no default setting. The range is 1 to 255.

Step 7

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 8

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 9

show ip pim rp mapping

Example:

Device# show ip pim rp mapping

Displays active RPs that are cached with associated multicast routing entries.

Step 10

show ip pim rp

Example:


Device# show ip pim rp

Displays the information cached in the routing table.

Step 11

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Adding Auto-RP to an Existing Sparse-Mode Cloud (CLI)

This section contains suggestions for the initial deployment of Auto-RP into an existing sparse-mode cloud to minimize disruption of the existing multicast infrastructure.

This procedure is optional.

SUMMARY STEPS

enable
show running-config
configure terminal
ip pim send-rp-announce interface-id scope ttl group-list access-list-number interval seconds
access-list access-list-number {deny | permit} source [source-wildcard]
ip pim send-rp-discovery scope ttl
end
show running-config
show ip pim rp mapping
show ip pim rp
copy running-config startup-config

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

show running-config

Example:


Device# show running-config

Verifies that a default RP is already configured on all PIM devices and the RP in the sparse-mode network. It was previously configured with the ip pim rp-address global configuration command.

Note

This step is not required for spare-dense-mode environments.

The selected RP should have good connectivity and be available across the network. Use this RP for the global groups (for example, 224.x.x.x and other global groups). Do not reconfigure the group address range that this RP serves. RPs dynamically discovered through Auto-RP take precedence over statically configured RPs. Assume that it is desirable to use a second RP for the local groups.

Step 3

configure terminal

Example:


Device# configure terminal

Enters the global configuration mode.

Step 4

ip pim send-rp-announce interface-id scope ttl group-list access-list-number interval seconds

Example:


Device(config)# ip pim send-rp-announce gigabitethernet 
1/0/5 scope 20 group-list 10 interval 120

Configures another PIM device to be the candidate RP for local groups.

For interface-id , enter the interface type and number that identifies the RP address. Valid interfaces include physical ports, port channels, and VLANs.
For scope ttl , specify the time-to-live value in hops. Enter a hop count that is high enough so that the RP-announce messages reach all mapping agents in the network. There is no default setting. The range is 1 to 255.
For group-list access-list-number , enter an IP standard access list number from 1 to 99. If no access list is configured, the RP is used for all groups.
For interval seconds , specify how often the announcement messages must be sent. The default is 60 seconds. The range is 1 to 16383.

Step 5

access-list access-list-number {deny | permit} source [source-wildcard]

Example:


Device(config)# access-list 10 
permit  224.0.0.0 15.255.255.255

Creates a standard access list, repeating the command as many times as necessary.

For access-list-number , enter the access list number specified in Step 3.
The deny keyword denies access if the conditions are matched.
The permit keyword permits access if the conditions are matched.
For source , enter the multicast group address range for which the RP should be used.
(Optional) For source-wildcard , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore.

Recall that the access list is always terminated by an implicit deny statement for everything.

Step 6

ip pim send-rp-discovery scope ttl

Example:


Device(config)# ip pim send-rp-discovery scope 50

Finds a device whose connectivity is not likely to be interrupted, and assigns it the role of RP-mapping agent.

For scope ttl , specify the time-to-live value in hops to limit the RP discovery packets. All devices within the hop count from the source device receive the Auto-RP discovery messages. These messages tell other devices which group-to-RP mapping to use to avoid conflicts (such as overlapping group-to-RP ranges). There is no default setting. The range is 1 to 255.

Note

To remove the device as the RP-mapping agent, use the no ip pim send-rp-discovery global configuration command.

Step 7

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 8

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 9

show ip pim rp mapping

Example:

Device# 
show ip pim rp mapping

Displays active RPs that are cached with associated multicast routing entries.

Step 10

show ip pim rp

Example:


Device# show ip pim rp

Displays the information cached in the routing table.

Step 11

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Preventing Join Messages to False RPs (CLI)

Determine whether the ip pim accept-rp command was previously configured throughout the network by using the show running-config privileged EXEC command. If the ip pim accept-rp command is not configured on any device, this problem can be addressed later. In those routers or multilayer devices already configured with the ip pim accept-rp command, you must enter the command again to accept the newly advertised RP.

To accept all RPs advertised with Auto-RP and reject all other RPs by default, use the ip pim accept-rp auto-rp global configuration command.

This procedure is optional.

Filtering Incoming RP Announcement Messages (CLI)

You can add configuration commands to the mapping agents to prevent a maliciously configured router from masquerading as a candidate RP and causing problems.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
ip pim rp-announce-filter rp-list access-list-number group-list access-list-number
access-list access-list-number {deny | permit} source [source-wildcard]
end
show running-config
copy running-config startup-config

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 the global configuration mode.
Step 3	ip pim rp-announce-filter rp-list `access-list-number` group-list `access-list-number` Example: `Device(config)# ip pim rp-announce-filter rp-list 10 group-list 14`	Filters incoming RP announcement messages. Enter this command on each mapping agent in the network. Without this command, all incoming RP-announce messages are accepted by default. For rp-list `access-list-number` , configure an access list of candidate RP addresses that, if permitted, is accepted for the group ranges supplied in the group-list `access-list-number` variable. If this variable is omitted, the filter applies to all multicast groups. If more than one mapping agent is used, the filters must be consistent across all mapping agents to ensure that no conflicts occur in the group-to-RP mapping information.
Step 4	access-list `access-list-number` {deny \| permit} `source` [`source-wildcard`] Example: `Device(config)# access-list 10 permit 10.8.1.0 255.255.224.0`	Creates a standard access list, repeating the command as many times as necessary. For `access-list-number` , enter the access list number specified in Step 2. The deny keyword denies access if the conditions are matched. The permit keyword permits access if the conditions are matched. Create an access list that specifies from which routers and multilayer devices the mapping agent accepts candidate RP announcements (rp-list ACL). Create an access list that specifies the range of multicast groups from which to accept or deny (group-list ACL). For `source` , enter the multicast group address range for which the RP should be used. (Optional) For `source-wildcard` , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore. The access list is always terminated by an implicit deny statement for everything.
Step 5	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 6	show running-config Example: `Device# show running-config`	Verifies your entries.
Step 7	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Configuring PIMv2 BSR

The process for configuring PIMv2 BSR may involve the following optional tasks:

Defining the PIM domain border
Defining the IP multicast boundary
Configuring candidate BSRs
Configuring candidate RPs

Defining the PIM Domain Border (CLI)

Perform the following steps to configure the PIM domain border. This procedure is optional.

SUMMARY STEPS

enable
configure terminal
interface interface-id
ip pim bsr-border
end
show running-config
copy running-config startup-config

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 the global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet 1/0/1

Specifies the interface to be configured, and enters interface configuration mode.

Step 4

ip pim bsr-border

Example:


Device(config-if)# ip pim bsr-border

Defines a PIM bootstrap message boundary for the PIM domain.

Enter this command on each interface that connects to other bordering PIM domains. This command instructs the device to neither send nor receive PIMv2 BSR messages on this interface.

Note

To remove the PIM border, use the no ip pim bsr-border interface configuration command.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Defining the IP Multicast Boundary (CLI)

You define a multicast boundary to prevent Auto-RP messages from entering the PIM domain. You create an access list to deny packets destined for 224.0.1.39 and 224.0.1.40, which carry Auto-RP information.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
access-list access-list-number deny source [source-wildcard]
interface interface-id
ip multicast boundary access-list-number
end
show running-config
copy running-config startup-config

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 the global configuration mode.
Step 3	access-list `access-list-number` deny `source` [`source-wildcard`] Example: `Device(config)# access-list 12 deny 224.0.1.39 access-list 12 deny 224.0.1.40`	Creates a standard access list, repeating the command as many times as necessary. For `access-list-number` , the range is 1 to 99. The deny keyword denies access if the conditions are matched. For `source` , enter multicast addresses 224.0.1.39 and 224.0.1.40, which carry Auto-RP information. (Optional) For `source-wildcard` , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore. The access list is always terminated by an implicit deny statement for everything.
Step 4	interface `interface-id` Example: `Device(config)# interface gigabitethernet 1/0/1`	Specifies the interface to be configured, and enters interface configuration mode.
Step 5	ip multicast boundary `access-list-number` Example: `Device(config-if)# ip multicast boundary 12`	Configures the boundary, specifying the access list you created in Step 2.
Step 6	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 7	show running-config Example: `Device# show running-config`	Verifies your entries.
Step 8	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Configuring Candidate BSRs (CLI)

You can configure one or more candidate BSRs. The devices serving as candidate BSRs should have good connectivity to other devices and be in the backbone portion of the network.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
ip pim bsr-candidate interface-id hash-mask-length [priority]
end
show running-config
copy running-config startup-config

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 the global configuration mode.
Step 3	ip pim bsr-candidate `interface-id hash-mask-length` [`priority`] Example: `Device(config)# ip pim bsr-candidate gigabitethernet 1/0/3 28 100`	Configures your device to be a candidate BSR. For `interface-id` , enter the interface on this device from which the BSR address is derived to make it a candidate. This interface must be enabled with PIM. Valid interfaces include physical ports, port channels, and VLANs. For `hash-mask-length` , specify the mask length (32 bits maximum) that is to be ANDed with the group address before the hash function is called. All groups with the same seed hash correspond to the same RP. For example, if this value is 24, only the first 24 bits of the group addresses matter. (Optional) For `priority` , enter a number from 0 to 255. The BSR with the larger priority is preferred. If the priority values are the same, the device with the highest IP address is selected as the BSR. The default is 0.
Step 4	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 5	show running-config Example: `Device# show running-config`	Verifies your entries.
Step 6	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Configuring the Candidate RPs (CLI)

You can configure one or more candidate RPs. Similar to BSRs, the RPs should also have good connectivity to other devices and be in the backbone portion of the network. An RP can serve the entire IP multicast address space or a portion of it. Candidate RPs send candidate RP advertisements to the BSR.

This procedure is optional.

Before you begin

When deciding which devices should be RPs, consider these options:

In a network of Cisco routers and multilayer devices where only Auto-RP is used, any device can be configured as an RP.
In a network that includes only Cisco PIMv2 routers and multilayer devices and with routers from other vendors, any device can be used as an RP.
In a network of Cisco PIMv1 routers, Cisco PIMv2 routers, and routers from other vendors, configure only Cisco PIMv2 routers and multilayer devices as RPs.

SUMMARY STEPS

enable
configure terminal
ip pim rp-candidate interface-id [group-list access-list-number]
access-list access-list-number {deny | permit} source [source-wildcard]
end
show running-config
copy running-config startup-config

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 the global configuration mode.
Step 3	ip pim rp-candidate `interface-id` [group-list `access-list-number`] Example: `Device(config)# ip pim rp-candidate gigabitethernet 1/0/5 group-list 10`	Configures your device to be a candidate RP. For `interface-id` , specify the interface whose associated IP address is advertised as a candidate RP address. Valid interfaces include physical ports, port channels, and VLANs. (Optional) For group-list `access-list-number` , enter an IP standard access list number from 1 to 99. If no group-list is specified, the device is a candidate RP for all groups.
Step 4	access-list `access-list-number` {deny \| permit} `source` [`source-wildcard`] Example: `Device(config)# access-list 10 permit 239.0.0.0 0.255.255.255`	Creates a standard access list, repeating the command as many times as necessary. For `access-list-number` , enter the access list number specified in Step 2. The deny keyword denies access if the conditions are matched. The permit keyword permits access if the conditions are matched. For `source` , enter the number of the network or host from which the packet is being sent. (Optional) For `source-wildcard` , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore. The access list is always terminated by an implicit deny statement for everything.
Step 5	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 6	show running-config Example: `Device# show running-config`	Verifies your entries.
Step 7	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Configuring Sparse Mode with Auto-RP(CLI)

Before you begin

An interface configured in sparse-dense mode is treated in either sparse mode or dense mode of operation, depending on the mode in which the multicast group operates. You must decide how to configure your interfaces.
All access lists that are needed when Auto-RP is configured should be configured prior to beginning the configuration task.

Note

If a group has no known RP and the interface is configured to be sparse-dense mode, the interface is treated as if it were in dense mode, and data is flooded over the interface. To avoid this data flooding, configure the Auto-RP listener and then configure the interface as sparse mode.
When configuring Auto-RP, you must either configure the Auto-RP listener feature (Step 5) and specify sparse mode (Step 7) or specify sparse-dense mode (Step 8) .
When you configure sparse-dense mode, dense mode failover may result in a network dense-mode flood. To avoid this condition, use PIM sparse mode with the Auto-RP listener feature.

Follow this procedure to configure auto-rendezvous point (Auto-RP). Auto-RP can also be optionally used with anycast RP.

SUMMARY STEPS

enable
configure terminal
ip multicast-routing [distributed ]
Either perform Steps 5 through 7 or perform Steps 6 and 8.
ip pim autorp listener
interface type number
ip pim sparse-mode
ip pim sparse-dense-mode
exit
Repeat Steps 1 through 9 on all PIM interfaces.
ip pim send-rp-announce {interface-type interface-number | ip-address } scope ttl-value [group-list access-list ] [interval seconds ] [bidir ]
ip pim send-rp-discovery [interface-type interface-number ] scope ttl-value [interval seconds ]
ip pim rp-announce-filter rp-list access-list group-list access-list
no ip pim dm-fallback
interface type number
ip multicast boundary access-list [filter-autorp ]
end
show ip pim autorp
show ip pim rp [mapping ] [rp-address ]
show ip igmp groups [group-name | group-address | interface-type interface-number ] [detail ]
show ip mroute [group-address | group-name ] [source-address | source-name ] [interface-type interface-number ] [summary ] [count ] [active kbps ]

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

ip multicast-routing [distributed ]

Example:


Device(config)# ip multicast-routing

Enables IP multicast routing.

Use the distributed keyword to enabled Multicast Distributed Switching.

Step 4

Either perform Steps 5 through 7 or perform Steps 6 and 8.

--

Step 5

ip pim autorp listener

Example:


Device(config)# ip pim autorp listener

Causes IP multicast traffic for the two Auto-RP groups 224.0.1.39 and 224.0.1.40 to be PIM dense mode flooded across interfaces operating in PIM sparse mode.

Skip this step if you are configuring sparse-dense mode in Step 8.

Step 6

interface type number

Example:


Device(config)# interface Gigabitethernet 1/0/0

Selects an interface that is connected to hosts on which PIM can be enabled.

Step 7

ip pim sparse-mode

Example:


Device(config-if)# ip pim sparse-mode

Enables PIM sparse mode on an interface. When configuring Auto-RP in sparse mode, you must also configure the Auto-RP listener in the next step.

Skip this step if you are configuring sparse-dense mode in Step 8.

Step 8

ip pim sparse-dense-mode

Example:


Device(config-if)# ip pim sparse-dense-mode

Enables PIM sparse-dense mode on an interface.

Skip this step if you configured sparse mode in Step 7.

Step 9

exit

Example:


Device(config-if)# exit

Exits interface configuration mode and returns to global configuration mode.

Step 10

Repeat Steps 1 through 9 on all PIM interfaces.

--

Step 11

ip pim send-rp-announce {interface-type interface-number | ip-address } scope ttl-value [group-list access-list ] [interval seconds ] [bidir ]

Example:


Device(config)# ip pim send-rp-announce loopback0 scope 31 group-list 5

Sends RP announcements out all PIM-enabled interfaces.

Perform this step on the RP device only.
Use the interface-type and interface-number arguments to define which IP address is to be used as the RP address.
Use the ip-address argument to specify a directly connected IP address as the RP address.

Note

If the ip-address argument is configured for this command, the RP-announce message will be sourced by the interface to which this IP address is connected (that is, the source address in the IP header of the RP-announce message is the IP address of that interface).

This example shows that the interface is enabled with a maximum of 31 hops. The IP address by which the device wants to be identified as RP is the IP address associated with loopback interface 0. Access list 5 describes the groups for which this device serves as RP.

Step 12

ip pim send-rp-discovery [interface-type interface-number ] scope ttl-value [interval seconds ]

Example:


Device(config)# ip pim send-rp-discovery loopback 1 scope 31

Configures the device to be an RP mapping agent.

Perform this step on RP mapping agent devices or on combined RP/RP mapping agent devices.

Note

Auto-RP allows the RP function to run separately on one device and the RP mapping agent to run on one or multiple devices. It is possible to deploy the RP and the RP mapping agent on a combined RP/RP mapping agent device.

Use the optional interface-type and interface-number arguments to define which IP address is to be used as the source address of the RP mapping agent.
Use the scope keyword and ttl-value argument to specify the Time-to-Live (TTL) value in the IP header of Auto-RP discovery messages.
Use the optional interval keyword and seconds argument to specify the interval at which Auto-RP discovery messages are sent.

Note

Lowering the interval at which Auto-RP discovery messages are sent from the default value of 60 seconds results in more frequent floodings of the group-to-RP mappings. In some network environments, the disadvantages of lowering the interval (more control packet overhead) may outweigh the advantages (more frequent group-to-RP mapping updates).

The example shows limiting the Auto-RP discovery messages to 31 hops on loopback interface 1.

Step 13

ip pim rp-announce-filter rp-list access-list group-list access-list

Example:


Device(config)# ip pim rp-announce-filter rp-list 1 group-list 2

Filters incoming RP announcement messages sent from candidate RPs (C-RPs) to the RP mapping agent.

Perform this step on the RP mapping agent only.

Step 14

no ip pim dm-fallback

Example:


Device(config)# no ip pim dm-fallback

(Optional) Prevents PIM dense mode fallback.

Skip this step if all interfaces have been configured to operate in PIM sparse mode.

Note

The no ip pim dm-fallback command behavior is enabled by default if all the interfaces are configured to operate in PIM sparse mode (using the ip pim sparse-mode command).

Step 15

interface type number

Example:


Device(config)# interface gigabitethernet 1/0/0

Selects an interface that is connected to hosts on which PIM can be enabled.

Step 16

ip multicast boundary access-list [filter-autorp ]

Example:


Device(config-if)# ip multicast boundary 10 filter-autorp

Configures an administratively scoped boundary.

Perform this step on the interfaces that are boundaries to other devices.
The access list is not shown in this task.
An access list entry that uses the deny keyword creates a multicast boundary for packets that match that entry.

Step 17

end

Example:


Device(config-if)# end

Returns to global configuration mode.

Step 18

show ip pim autorp

Example:


Device# show ip pim autorp

(Optional) Displays the Auto-RP information.

Step 19

show ip pim rp [mapping ] [rp-address ]

Example:


Device# show ip pim rp mapping

(Optional) Displays RPs known in the network and shows how the device learned about each RP.

Step 20

show ip igmp groups [group-name | group-address | interface-type interface-number ] [detail ]

Example:


Device# show ip igmp groups

(Optional) Displays the multicast groups having receivers that are directly connected to the device and that were learned through Internet Group Management Protocol (IGMP).

A receiver must be active on the network at the time that this command is issued in order for receiver information to be present on the resulting display.

Step 21

show ip mroute [group-address | group-name ] [source-address | source-name ] [interface-type interface-number ] [summary ] [count ] [active kbps ]

Example:


Device# show ip mroute cbone-audio

(Optional) Displays the contents of the IP multicast routing (mroute) table.

Delaying the Use of PIM Shortest-Path Tree (CLI)

Perform these steps to configure a traffic rate threshold that must be reached before multicast routing is switched from the source tree to the shortest-path tree.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
access-list access-list-number {deny | permit} source [source-wildcard]
ip pim spt-threshold {kbps | infinity} [group-list access-list-number]
end
show running-config
copy running-config startup-config

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

access-list access-list-number {deny | permit} source [source-wildcard]

Example:


Device(config)# access-list 16 permit 225.0.0.0 0.255.255.255

Creates a standard access list.

For access-list-number , the range is 1 to 99.
The deny keyword denies access if the conditions are matched.
The permit keyword permits access if the conditions are matched.
For source , specify the multicast group to which the threshold will apply.
(Optional) For source-wildcard , enter the wildcard bits in dotted decimal notation to be applied to the source. Place ones in the bit positions that you want to ignore.

The access list is always terminated by an implicit deny statement for everything.

Step 4

ip pim spt-threshold {kbps | infinity} [group-list access-list-number]

Example:


Device(config)# ip pim spt-threshold 
infinity group-list 16

Specifies the threshold that must be reached before moving to shortest-path tree (spt).

For kbps , specify the traffic rate in kilobits per second. The default is 0 kbps.

Note

Because of device hardware limitations, 0 kbps is the only valid entry even though the range is 0 to 4294967.

Specify infinity if you want all sources for the specified group to use the shared tree, never switching to the source tree.
(Optional) For group-list access-list-number , specify the access list created in Step 2. If the value is 0 or if the group list is not used, the threshold applies to all groups.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Modifying the PIM Router-Query Message Interval (CLI)

PIM routers and multilayer devices send PIM router-query messages to find which device will be the designated router (DR) for each LAN segment (subnet). The DR is responsible for sending IGMP host-query messages to all hosts on the directly connected LAN.

With PIM DM operation, the DR has meaning only if IGMPv1 is in use. IGMPv1 does not have an IGMP querier election process, so the elected DR functions as the IGMP querier. With PIM-SM operation, the DR is the device that is directly connected to the multicast source. It sends PIM register messages to notify the RP that multicast traffic from a source needs to be forwarded down the shared tree. In this case, the DR is the device with the highest IP address.

This procedure is optional.

SUMMARY STEPS

enable
configure terminal
interface interface-id
ip pim query-interval seconds
end
show ip igmp interface [interface-id]
copy running-config startup-config

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 the global configuration mode.
Step 3	interface `interface-id` Example: `Device(config)# interface gigabitethernet 1/0/1`	Specifies the interface to be configured, and enters interface configuration mode.
Step 4	ip pim query-interval `seconds` Example: `Device(config-if)# ip pim query-interval 45`	Configures the frequency at which the device sends PIM router-query messages. The default is 30 seconds. The range is 1 to 65535.
Step 5	end Example: `Device(config)# end`	Returns to privileged EXEC mode.
Step 6	show ip igmp interface [`interface-id`] Example: `Device# show ip igmp interface`	Verifies your entries.
Step 7	copy running-config startup-config Example: `Device# copy running-config startup-config`	(Optional) Saves your entries in the configuration file.

Verifying IP Multicast Operation in a PIM-SM or a PIM-SSM Network

When you verify the operation of IP multicast in a PIM-SM network environment or in an PIM-SSM network environment, a useful approach is to begin the verification process on the last hop router, and then continue the verification process on the routers along the SPT until the first hop router has been reached. The goal of the verification is to ensure that IP multicast traffic is being routed properly through an IP multicast network.

Perform the following optional tasks to verify IP multicast operation in a PIM-SM or a PIM-SSM network. The steps in these tasks help to locate a faulty hop when sources and receivers are not operating as expected.

Note

If packets are not reaching their expected destinations, you might want consider disabling IP multicast fast switching, which would place the router in process switching mode. If packets begin reaching their proper destinations after IP multicast fast switching has been disabled, then the issue most likely was related to IP multicast fast switching.

Verifying IP Multicast on the First Hop Router

Enter these commands on the first hop router to verify IP multicast operations on the first hop router:

SUMMARY STEPS

enable
show ip mroute [group-address ]
show ip mroute active [kb/s ]

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

show ip mroute [group-address ]

Example:

Device# show ip mroute 239.1.2.3
(*, 239.1.2.3), 00:18:10/stopped, RP 172.16.0.1, flags: SPF
  Incoming interface: Serial1/0, RPF nbr 172.31.200.2
  Outgoing interface list: Null
 
(10.0.0.1, 239.1.2.3), 00:18:10/00:03:22, flags: FT
  Incoming interface: GigabitEthernet0/0/0, RPF nbr 0.0.0.0  
  Outgoing interface list:
    Serial1/0, Forward/Sparse-Dense, 00:18:10/00:03:19

Confirms that the F flag has been set for mroutes on the first hop router.

Step 3

show ip mroute active [kb/s ]

Example:

Device# show ip mroute active
Active IP Multicast Sources - sending >= 4 kbps
 
Group: 239.1.2.3, (?)
   Source: 10.0.0.1 (?)
     Rate: 20 pps/4 kbps(1sec), 4 kbps(last 30 secs), 4 kbps(life avg)

Displays information about active multicast sources sending to groups. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the show ip mroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

Verifying IP Multicast on Routers Along the SPT

Enter these commands on routers along the SPT to verify IP multicast operations on routers along the SPT in a PIM-SM or PIM-SSM network:

SUMMARY STEPS

enable
show ip mroute [group-address ]
show ip mroute active

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

show ip mroute [group-address ]

Example:

Device# show ip mroute 239.1.2.3
(*, 239.1.2.3), 00:17:56/00:03:02, RP 172.16.0.1, flags: S
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    GigabitEthernet0/0/0, Forward/Sparse-Dense, 00:17:56/00:03:02
 
(10.0.0.1, 239.1.2.3), 00:15:34/00:03:28, flags: T
  Incoming interface: Serial1/0, RPF nbr 172.31.200.1  
  Outgoing interface list:
    GigabitEthernet0/0/0, Forward/Sparse-Dense, 00:15:34/00:03:02

Confirms the RPF neighbor towards the source for a particular group or groups.

Step 3

show ip mroute active

Example:

Device# show ip mroute active
Active IP Multicast Sources - sending >= 4 kbps
 
Group: 239.1.2.3, (?)
   Source: 10.0.0.1 (?)
     Rate: 20 pps/4 kbps(1sec), 4 kbps(last 30 secs), 4 kbps(life avg)

Displays information about active multicast sources sending to groups. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the show ip mroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

Verifying IP Multicast Operation on the Last Hop Router

Enter these commands on the last hop router to verify IP multicast operations on the last hop router:

SUMMARY STEPS

enable
show ip igmp groups
show ip pim rp mapping
show ip mroute
show ip interface [type number ]
show ip mfib
show ip pim interface count
show ip mroute count
show ip mroute active [kb/s ]

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

show ip igmp groups

Example:

Device# show ip igmp groups
IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter
239.1.2.3        GigabitEthernet1/0/0     00:05:14  00:02:14  10.1.0.6
224.0.1.39       GigabitEthernet0/0/0     00:09:11  00:02:08  172.31.100.1

Verifies IGMP memberships on the last hop router. This information will confirm the multicast groups with receivers that are directly connected to the last hop router and that are learned through IGMP.

Step 3

show ip pim rp mapping

Example:

Device# show ip pim rp mapping
PIM Group-to-RP Mappings
 
Group(s) 224.0.0.0/4
  RP 172.16.0.1 (?), v2v1 
    Info source: 172.16.0.1 (?), elected via Auto-RP
         Uptime: 00:09:11, expires: 00:02:47

Confirms that the group-to-RP mappings are being populated correctly on the last hop router.

Note

Ignore this step if you are verifying a last hop router in a PIM-SSM network. The show ip pim rp mapping command does not work with routers in a PIM-SSM network because PIM-SSM does not use RPs. In addition, if configured correctly, PIM-SSM groups do not appear in the output of the show ip pim rp mapping command.

Step 4

show ip mroute

Example:

Device# show ip mroute
(*, 239.1.2.3), 00:05:14/00:03:04, RP 172.16.0.1, flags: SJC
  Incoming interface: GigabitEthernet0/0/0, RPF nbr 172.31.100.1
  Outgoing interface list:
  GigabitEthernet1/0, Forward/Sparse-Dense, 00:05:10/00:03:04
 
(10.0.0.1, 239.1.2.3), 00:02:49/00:03:29, flags: T  
  Incoming interface: GigabitEthernet0/0/0, RPF nbr 172.31.100.1  
  Outgoing interface list:
  GigabitEthernet1/0, Forward/Sparse-Dense, 00:02:49/00:03:04
 
(*, 224.0.1.39), 00:10:05/stopped, RP 0.0.0.0, flags: DC
  Incoming interface: Null, RPF nbr 0.0.0.0
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Sparse-Dense, 00:05:15/00:00:00
    GigabitEthernet0/0, Forward/Sparse-Dense, 00:10:05/00:00:00
 
(172.16.0.1, 224.0.1.39), 00:02:00/00:01:33, flags: PTX
  Incoming interface: GigabitEthernet0/0/0, RPF nbr 172.31.100.1

Verifies that the mroute table is being populated properly on the last hop router.

Step 5

show ip interface [type number ]

Example:

Device# show ip interface GigabitEthernet 0/0/0
GigabitEthernet0/0 is up, line protocol is up
  Internet address is 172.31.100.2/24
  Broadcast address is 255.255.255.255
  Address determined by setup command
  MTU is 1500 bytes
  Helper address is not set
  Directed broadcast forwarding is disabled
  Multicast reserved groups joined: 224.0.0.1 224.0.0.22 224.0.0.13
      224.0.0.5 224.0.0.6
  Outgoing access list is not set
  Inbound  access list is not set
  Proxy ARP is enabled
  Local Proxy ARP is disabled
  Security level is default
  Split horizon is enabled
  ICMP redirects are always sent
  ICMP unreachables are always sent
  ICMP mask replies are never sent
  IP fast switching is enabled
  IP fast switching on the same interface is disabled
  IP Flow switching is disabled
  IP CEF switching is disabled
  IP Fast switching turbo vector
  IP multicast fast switching is enabled
  IP multicast distributed fast switching is disabled
  IP route-cache flags are Fast
  Router Discovery is disabled
  IP output packet accounting is disabled
  IP access violation accounting is disabled
  TCP/IP header compression is disabled
  RTP/IP header compression is disabled
  Policy routing is disabled
  Network address translation is disabled
  WCCP Redirect outbound is disabled
  WCCP Redirect inbound is disabled
  WCCP Redirect exclude is disabled
  BGP Policy Mapping is disabled

Verifies that multicast fast switching is enabled for optimal performance on the outgoing interface on the last hop router.

Note

Using the no ip mroute-cache interface command disables IP multicast fast-switching. When IP multicast fast switching is disabled, packets are forwarded through the process-switched path.

Step 6

show ip mfib

Example:

Device# show ip mfib

Displays the forwarding entries and interfaces in the IP Multicast Forwarding Information Base (MFIB).

Step 7

show ip pim interface count

Example:

Device# show ip pim interface count
 
State: * - Fast Switched, D - Distributed Fast Switched
       H - Hardware Switching Enabled
Address          Interface                FS Mpackets In/Out
172.31.100.2     GigabitEthernet0/0/0     *   4122/0
10.1.0.1         GigabitEthernet1/0/0     *   0/3193

Confirms that multicast traffic is being forwarded on the last hop router.

Step 8

show ip mroute count

Example:

Device# show ip mroute count
IP Multicast Statistics
6 routes using 4008 bytes of memory
3 groups, 1.00 average sources per group
Forwarding Counts: Pkt Count/Pkts per second/Avg Pkt Size/Kilobits per second
Other counts: Total/RPF failed/Other drops(OIF-null, rate-limit etc)
 
Group: 239.1.2.3, Source count: 1, Packets forwarded: 3165, Packets received: 3165
  RP-tree: Forwarding: 0/0/0/0, Other: 0/0/0
  Source: 10.0.0.1/32, Forwarding: 3165/20/28/4, Other: 0/0/0  
 
Group: 224.0.1.39, Source count: 1, Packets forwarded: 21, Packets received: 120
  Source: 172.16.0.1/32, Forwarding: 21/1/48/0, Other: 120/0/99
 
Group: 224.0.1.40, Source count: 1, Packets forwarded: 10, Packets received: 10
  Source: 172.16.0.1/32, Forwarding: 10/1/48/0, Other: 10/0/0

Confirms that multicast traffic is being forwarded on the last hop router.

Step 9

show ip mroute active [kb/s ]

Example:

Device# show ip mroute active
Active IP Multicast Sources - sending >= 4 kbps
 
Group: 239.1.2.3, (?)
   Source: 10.0.0.1 (?)
     Rate: 20 pps/4 kbps(1sec), 4 kbps(last 50 secs), 4 kbps(life avg)

Displays information about active multicast sources sending traffic to groups on the last hop router. The output of this command provides information about the multicast packet rate for active sources.

Note

By default, the output of the show ip mroute command with the active keyword displays information about active sources sending traffic to groups at a rate greater than or equal to 4 kb/s. To display information about active sources sending low-rate traffic to groups (that is, traffic less than 4 kb/s), specify a value of 1 for the kb/s argument. Specifying a value of 1 for this argument displays information about active sources sending traffic to groups at a rate equal to or greater than 1 kb/s, which effectively displays information about all possible active source traffic.

Using PIM-Enabled Routers to Test IP Multicast Reachability

If all the PIM-enabled routers and access servers that you administer are members of a multicast group, pinging that group causes all routers to respond, which can be a useful administrative and debugging tool.

To use PIM-enabled routers to test IP multicast reachability, perform the following tasks:

Configuring Routers to Respond to Multicast Pings

SUMMARY STEPS

enable
configure terminal
interface type number
ip igmp join-group group-address
Repeat Step 3 and Step 4 for each interface on the router participating in the multicast network.
end

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:


Device(config)# interface gigabitethernet 1/0/0

Enters interface configuration mode.

For the type and number arguments, specify an interface that is directly connected to hosts or is facing hosts.

Step 4

ip igmp join-group group-address

Example:


Device(config-if)# ip igmp join-group 225.2.2.2

(Optional) Configures an interface on the router to join the specified group.

For the purpose of this task, configure the same group address for the group-address argument on all interfaces on the router participating in the multicast network.

Note

With this method, the router accepts the multicast packets in addition to forwarding them. Accepting the multicast packets prevents the router from fast switching.

Step 5

Repeat Step 3 and Step 4 for each interface on the router participating in the multicast network.

--

Step 6

end

Example:


Device(config-if)# end

Ends the current configuration session and returns to privileged EXEC mode.

Pinging Routers Configured to Respond to Multicast Pings

on a router to initiate a ping test to the routers configured to respond to multicast pings. This task is used to test IP multicast reachability in a network.

SUMMARY STEPS

enable
ping group-address

DETAILED STEPS

Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

ping group-address

Example:


Device# ping 225.2.2.2

Pings an IP multicast group address.

A successful response indicates that the group address is functioning.

Monitoring PIM Information

Use the privileged EXEC commands in the following table to monitor your PIM configurations.

Table 2. PIM Monitoring Commands
Command	Purpose
show ip pim all-vrfs tunnel [tunnel `tunnel_number` \| verbose]	Displays all VRFs.
show ip pim autorp	Displays global auto-RP information.
show ip pim boundary	Displays information about mroutes filtered by administratively scoped IPv4 multicast boundaries configured on an interface.
show ip pim interface	Displays information about interfaces configured for Protocol Independent Multicast (PIM).
show ip pim neighbor	Displays the PIM neighbor information.
show ip pim rp[`group-name` \| `group-address`]	Displays RP routers associated with a sparse-mode multicast group. This command is available in all software images.
show ip pim tunnel [tunnel \| verbose]	Displays information about Protocol Independent Multicast (PIM) tunnel interfaces
show ip pim vrf { word { all-vrfs \| autorp \| boundary \| bsr-router \| interface \| mdt \| neighbor \| rp \| rp-hash \| tunnel } }	Displays the VPN routing/forwarding instance.
show ip igmp groups detail	Displays the interested clients that have joined the specific multicast source group.

Monitoring the RP Mapping and BSR Information

Use the privileged EXEC mode in the following table to verify the consistency of group-to-RP mappings:

Table 3. RP Mapping Monitoring Commands
Command	Purpose
show ip pim rp [ `hostname` or `IP address` \| mapping [ `hostname` or `IP address` \| elected \| in-use ] \| metric [ `hostname` or `IP address` ] ]	Displays all available RP mappings and metrics. This tells you how the device learns of the RP (through the BSR or the Auto-RP mechanism). (Optional) For the `hostname` , specify the IP name of the group about which to display RPs. (Optional) For the `IP address` , specify the IP address of the group about which to display RPs. (Optional) Use the mapping keyword to display all group-to-RP mappings of which the Cisco device is aware (either configured or learned from Auto-RP). (Optional) Use the metric keyword to display the RP RPF metric.
show ip pim rp-hash `group`	Displays the RP that was selected for the specified group. That is, on a PIMv2 router or multilayer device, confirms that the same RP is the one that a PIMv1 system chooses. For `group` , enter the group address for which to display RP information.

Use the privileged EXEC commands in the following table to monitor BSR information:

Table 4. BSR Monitoring Commands
Command	Purpose
show ip pim bsr	Displays information about the elected BSR.
show ip pim bsr-router	Displays information about the BSRv2.

Troubleshooting PIMv1 and PIMv2 Interoperability Problems

When debugging interoperability problems between PIMv1 and PIMv2, check these in the order shown:

Verify RP mapping with the show ip pim rp-hash privileged EXEC command, making sure that all systems agree on the same RP for the same group.
Verify interoperability between different versions of DRs and RPs. Make sure that the RPs are interacting with the DRs properly (by responding with register-stops and forwarding decapsulated data packets from registers).

Example: Enabling PIM Stub Routing

In this example, IP multicast routing is enabled, Switch A PIM uplink port 25 is configured as a routed uplink port with spare-dense-mode enabled. PIM stub routing is enabled on the VLAN 100 interfaces and on Gigabit Ethernet port 20.


Device(config)# ip multicast-routing distributed
Device(config)# interface GigabitEthernet3/0/25
Device(config-if)# no switchport
Device(config-if)# ip address 3.1.1.2 255.255.255.0
Device(config-if)# ip pim sparse-dense-mode
Device(config-if)# exit
Device(config)# interface vlan100
Device(config-if)# ip pim passive
Device(config-if)# exit
Device(config)# interface GigabitEthernet3/0/20
Device(config-if)# ip pim passive
Device(config-if)# exit
Device(config)# interface vlan100
Device(config-if)# ip address 100.1.1.1 255.255.255.0
Device(config-if)# ip pim passive
Device(config-if)# exit
Device(config)# interface GigabitEthernet3/0/20
Device(config-if)# no switchport
Device(config-if)# ip address 10.1.1.1 255.255.255.0
Device(config-if)# ip pim passive
Device(config-if)# end

Example: Verifying PIM Stub Routing

To verify that PIM stub is enabled for each interface, use the show ip pim interfac e privileged EXEC command:


Device# show ip pim interface
Address Interface Ver/ Nbr Query DR DR
Mode Count Intvl Prior
3.1.1.2 GigabitEthernet3/0/25 v2/SD 1 30 1 3.1.1.2
100.1.1.1 Vlan100 v2/P 0 30 1 100.1.1.1
10.1.1.1 GigabitEthernet3/0/20 v2/P 0 30 1 10.1.1.1

Example: Manually Assigning an RP to Multicast Groups

This example shows how to configure the address of the RP to 147.106.6.22 for multicast group 225.2.2.2 only:


Device(config)# access-list 1 permit 225.2.2.2 0.0.0.0
Device(config)# ip pim rp-address 147.106.6.22 1

Example: Configuring Auto-RP

This example shows how to send RP announcements out all PIM-enabled interfaces for a maximum of 31 hops. The IP address of port 1 is the RP. Access list 5 describes the group for which this device serves as RP:


Device(config)# ip pim send-rp-announce gigabitethernet1/0/1 scope 31 group-list 5
Device(config)# access-list 5 permit 224.0.0.0 15.255.255.255

Example: Sparse Mode with Auto-RP

The following example configures sparse mode with Auto-RP:


ip multicast-routing 
ip pim autorp listener 
ip pim send-rp-announce Loopback0 scope 16 group-list 1 
ip pim send-rp-discovery Loopback1 scope 16 
no ip pim dm-fallback
access-list 1 permit 239.254.2.0 0.0.0.255 
access-list 1 permit 239.254.3.0 0.0.0.255
.
.
.
access-list 10 permit 224.0.1.39
access-list 10 permit 224.0.1.40
access-list 10 permit 239.254.2.0 0.0.0.255
access-list 10 permit 239.254.3.0 0.0.0.255

Example: Defining the IP Multicast Boundary to Deny Auto-RP Information

This example shows a portion of an IP multicast boundary configuration that denies Auto-RP information:


Device(config)# access-list 1 deny 224.0.1.39
Device(config)# access-list 1 deny 224.0.1.40
Device(config)# access-list 1 permit all
Device(config)# interface gigabitethernet1/0/1
Device(config-if)# ip multicast boundary 1

Example: Filtering Incoming RP Announcement Messages

This example shows a sample configuration on an Auto-RP mapping agent that is used to prevent candidate RP announcements from being accepted from unauthorized candidate RPs:


Device(config)# ip pim rp-announce-filter rp-list 10 group-list 20
Device(config)# access-list 10 permit host 172.16.5.1
Device(config)# access-list 10 permit host 172.16.2.1
Device(config)# access-list 20 deny 239.0.0.0 0.0.255.255
Device(config)# access-list 20 permit 224.0.0.0 15.255.255.255

The mapping agent accepts candidate RP announcements from only two devices, 172.16.5.1 and 172.16.2.1. The mapping agent accepts candidate RP announcements from these two devices only for multicast groups that fall in the group range of 224.0.0.0 to 239.255.255.255. The mapping agent does not accept candidate RP announcements from any other devices in the network. Furthermore, the mapping agent does not accept candidate RP announcements from 172.16.5.1 or 172.16.2.1 if the announcements are for any groups in the 239.0.0.0 through 239.255.255.255 range. This range is the administratively scoped address range.

Example: Preventing Join Messages to False RPs

If all interfaces are in sparse mode, use a default-configured RP to support the two well-known groups 224.0.1.39 and 224.0.1.40. Auto-RP uses these two well-known groups to collect and distribute RP-mapping information. When this is the case and the ip pim accept-rp auto-rp command is configured, another ip pim accept-rp command accepting the RP must be configured as follows:


Device(config)# ip pim accept-rp 172.10.20.1 1
Device(config)# access-list 1 permit 224.0.1.39
Device(config)# access-list 1 permit 224.0.1.40

Example: Configuring Candidate BSRs

This example shows how to configure a candidate BSR, which uses the IP address 172.21.24.18 on a port as the advertised BSR address, uses 30 bits as the hash-mask-length, and has a priority of 10.


Device(config)# interface gigabitethernet1/0/2
Device(config-if)# ip address 172.21.24.18 255.255.255.0
Device(config-if)# ip pim sparse-dense-mode
Device(config-if)# ip pim bsr-candidate gigabitethernet1/0/2 30 10

Example: Configuring Candidate RPs

This example shows how to configure the device to advertise itself as a candidate RP to the BSR in its PIM domain. Standard access list number 4 specifies the group prefix associated with the RP that has the address identified by a port. That RP is responsible for the groups with the prefix 239.


Device(config)# ip pim rp-candidate gigabitethernet1/0/2 group-list 4
Device(config)# access-list 4 permit 239.0.0.0 0.255.255.255

Additional References

Error Message Decoder


Description	Link
To help you research and resolve system error messages in this release, use the Error Message Decoder tool.	https://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi

Standards and RFCs


Standard/RFC	Title
PIM is defined in RFC 4601 and in these Internet Engineering Task Force (IETF) Internet drafts.	Protocol Independent Multicast (PIM): Motivation and Architecture Protocol Independent Multicast (PIM), Dense Mode Protocol Specification Protocol Independent Multicast (PIM), Sparse Mode Protocol Specification draft-ietf-idmr-igmp-v2-06.txt, Internet Group Management Protocol, Version 2 draft-ietf-pim-v2-dm-03.txt, PIM Version 2 Dense Mode

MIBs


MIB	MIBs Link
All supported MIBs for this release.	To locate and download MIBs for selected platforms, Cisco IOS 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 website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.	http://www.cisco.com/support

Feature History and Information for PIM


Release	Modification
Cisco IOS XE 3.3SECisco IOS XE 3.3SE	This feature was introduced.

Related Topic	Document Title
For complete syntax and usage information for the commands used in this chapter.	IP Multicast Routing Command Reference (Catalyst 3650 Switches)
IGMP Helper command syntax and usage information.	IP Multicast Routing Command Reference (Catalyst 3650 Switches)
Multicast Source Discovery Protocol (MSDP)	IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3E (Catalyst 3650 Switches)
Enhanced Interior Gateway Routing Protocol (EIGRP) stub routing	IP Routing: EIGRP Configuration Guide, Cisco IOS XE Release 3E (Catalyst 3650 Switches)
Open Shortest Path First (OSPF) stub routing	IP Routing: OSPF Configuration Guide, Cisco IOS XE 3E (Catalyst 3650 Switches)
Cisco IOS commands	Cisco IOS Master Commands List, All Releases
Cisco IOS IP SLAs commands	Cisco IOS IP Multicast Command Reference

Bias-Free Language

Results

Chapter: Configuring PIM

Configuring PIM

Finding Feature Information

Prerequisites for PIM

Restrictions for PIM

PIMv1 and PIMv2 Interoperability

Restrictions for Configuring PIM Stub Routing

Restrictions for Configuring Auto-RP and BSR

Restrictions for Configuring Auto-RP

Restrictions for Configuring BSR

Restrictions and Guidelines for Configuring Auto-RP and BSR

Restrictions for Auto-RP Enhancement

Protocol Independent Multicast Overview

PIM Dense Mode

PIM Sparse Mode

Multicast Source Discovery Protocol (MSDP)

Sparse-Dense Mode

PIM Versions

PIM Stub Routing

IGMP Helper

Rendezvous Points

Auto-RP

The Role of Auto-RP in a PIM Network

Multicast Boundaries

Sparse-Dense Mode for Auto-RP

Auto-RP Benefits

Benefits of Auto-RP in a PIM Network

PIMv2 Bootstrap Router

PIM Domain Border

Multicast Forwarding

Multicast Distribution Source Tree

Multicast Distribution Shared Tree

Source Tree Advantage

Shared Tree Advantage

PIM Shared Tree and Source Tree

Reverse Path Forwarding

RPF Check

Default PIM Routing Configuration

Enabling PIM Stub Routing (CLI)

SUMMARY STEPS

DETAILED STEPS

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Configuring a Rendezvous Point

Manually Assigning an RP to Multicast Groups (CLI)

SUMMARY STEPS

DETAILED STEPS

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Setting Up Auto-RP in a New Internetwork (CLI)

SUMMARY STEPS

DETAILED STEPS

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Example:

Adding Auto-RP to an Existing Sparse-Mode Cloud (CLI)