Catalyst 4500 Series Switch Software Configuration Guide, 12.2(40)SG
Configuring IP Multicast
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Configuring IP Multicast

Table Of Contents

Configuring IP Multicast

Overview of IP Multicast

IP Multicast Protocols

Internet Group Management Protocol

Protocol-Independent Multicast

IGMP Snooping and CGMP

IP Multicast on the Catalyst 4500 Series Switch

CEF, MFIB, and Layer 2 Forwarding

IP Multicast Tables

Hardware and Software Forwarding

Non-Reverse Path Forwarding Traffic

Multicast Fast Drop

Multicast Forwarding Information Base

S/M, 224/4

Unsupported Features

Configuring IP Multicast Routing

Default Configuration in IP Multicast Routing

Enabling IP Multicast Routing

Enabling PIM on an Interface

Enabling Dense Mode

Enabling Sparse Mode

Enabling Sparse-Dense Mode

Enabling PIM-SSM mapping

Monitoring and Maintaining IP Multicast Routing

Displaying System and Network Statistics

Displaying the Multicast Routing Table

Displaying IP MFIB

Displaying IP MFIB Fast Drop

Displaying PIM Statistics

Clearing Tables and Databases

Configuration Examples

PIM Dense Mode Example

PIM Sparse Mode Example

BSR Configuration Example


Configuring IP Multicast


This chapter describes IP multicast routing on the Catalyst 4500 series switch. It also provides procedures and examples to configure IP multicast routing.


Note For more detailed information on IP Multicast, refer to this URL:

http://www.cisco.com/en/US/products/ps6552/products_ios_technology_home.html.



Note For complete syntax and usage information for the switch commands used in this chapter, first look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products//hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it will be found in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html


This chapter includes the following major sections:

Overview of IP Multicast

Configuring IP Multicast Routing

Monitoring and Maintaining IP Multicast Routing

Configuration Examples

Overview of IP Multicast

This section includes these subsections:

IP Multicast Protocols

IP Multicast on the Catalyst 4500 Series Switch, page 29-4

Unsupported Features

At one end of the IP communication spectrum is IP unicast, where a source IP host sends packets to a specific destination IP host. In IP unicast, the destination address in the IP packet is the address of a single, unique host in the IP network. These IP packets are forwarded across the network from the source to the destination host by routers. At each point on the path between source and destination, a router uses a unicast routing table to make unicast forwarding decisions, based on the IP destination address in the packet.

At the other end of the IP communication spectrum is an IP broadcast, where a source host sends packets to all hosts on a network segment. The destination address of an IP broadcast packet has the host portion of the destination IP address set to all ones and the network portion set to the address of the subnet. IP hosts, including routers, understand that packets, which contain an IP broadcast address as the destination address, are addressed to all IP hosts on the subnet. Unless specifically configured otherwise, routers do not forward IP broadcast packets, so IP broadcast communication is normally limited to a local subnet.

IP multicasting falls between IP unicast and IP broadcast communication. IP multicast communication enables a host to send IP packets to a group of hosts anywhere within the IP network. To send information to a specific group, IP multicast communication uses a special form of IP destination address called an IP multicast group address. The IP multicast group address is specified in the IP destination address field of the packet.

To multicast IP information, Layer 3 switches and routers must forward an incoming IP packet to all output interfaces that lead to members of the IP multicast group. In the multicasting process on the Catalyst 4000 family switch, a packet is replicated in the Integrated Switching Engine, forwarded to the appropriate output interfaces, and sent to each member of the multicast group.

It is not uncommon for people to think of IP multicasting and video conferencing as almost the same thing. Although the first application in a network to use IP multicast is often video conferencing, video is only one of many IP multicast applications that can add value to a company's business model. Other IP multicast applications that have potential for improving productivity include multimedia conferencing, data replication, real-time data multicasts, and simulation applications.

This section contains the following subsections:

IP Multicast Protocols

IP Multicast on the Catalyst 4500 Series Switch, page 29-4

Unsupported Features

IP Multicast Protocols

The Catalyst 4000 family switch primarily uses these protocols to implement IP multicast routing:

Internet Group Management Protocol (IGMP)

Protocol Independent Multicast (PIM)

IGMP snooping and Cisco Group Management Protocol

Figure 29-1 shows where these protocols operate within the IP multicast environment.

Figure 29-1 IP Multicast Routing Protocols

Internet Group Management Protocol

IGMP messages are used by IP multicast hosts to send their local Layer 3 switch or router a request to join a specific multicast group and begin receiving multicast traffic. With some extensions in IGMPv2, IP hosts can also send a request to a Layer 3 switch or router to leave an IP multicast group and not receive the multicast group traffic.

Using the information obtained via IGMP, a Layer 3 switch or router maintains a list of multicast group memberships on a per-interface basis. A multicast group membership is active on an interface if at least one host on the interface sends an IGMP request to receive multicast group traffic.

Protocol-Independent Multicast

PIM is protocol independent because it can leverage whichever unicast routing protocol is used to populate the unicast routing table, including EIGRP, OSPF, BGP, or static route, to support IP multicast. PIM also uses a unicast routing table to perform the reverse path forwarding (RPF) check function instead of building a completely independent multicast routing table. PIM does not send and receive multicast routing updates between routers like other routing protocols do.

PIM Dense Mode

PIM Dense Mode (PIM-DM) uses a push model to flood multicast traffic to every corner of the network. PIM-DM is intended for networks in which most LANs need to receive the multicast, such as LAN TV and corporate or financial information broadcasts. It can be an efficient delivery mechanism if there are active receivers on every subnet in the network.

For more detailed information on PIM Dense Mode, refer to this URL:

http://www.cisco.com/en/US/docs/ios-xml/ios/ipmulti_optim/configuration/12-2sx/imc_pim_dense_rfrsh.html

PIM Sparse Mode

PIM Sparse Mode (PIM-SM) uses a pull model to deliver multicast traffic. Only networks with active receivers that have explicitly requested the data will be forwarded the traffic. PIM-SM is intended for networks with several different multicasts, such as desktop video conferencing and collaborative computing, that go to a small number of receivers and are typically in progress simultaneously.

IGMP Snooping and CGMP

IGMP snooping is used for multicasting in a Layer 2 switching environment. With IGMP snooping, a Layer 3 switch or router examines Layer 3 information in the IGMP packets in transit between hosts and a router. When the switch receives the IGMP Host Report from a host for a particular multicast group, the switch adds the host's port number to the associated multicast table entry. When the switch receives the IGMP Leave Group message from a host, it removes the host's port from the table entry.

Because IGMP control messages are transmitted as multicast packets, they are indistinguishable from multicast data if only the Layer 2 header is examined. A switch running IGMP snooping examines every multicast data packet to determine whether it contains any pertinent IGMP control information. If IGMP snooping is implemented on a low end switch with a slow CPU, performance could be severely impacted when data is transmitted at high rates. On the Catalyst 4500 series switches, IGMP snooping is implemented in the forwarding ASIC, so it does not impact the forwarding rate.


Note A Catalyst 4000 family switch can act as a CGMP server for switches that do not support IGMP snooping, such as Catalyst 4500 family switches with Supervisor Engine I and Supervisor Engine II. You cannot configure the switch as a CGMP client. To configure a Catalyst 4000 family switch as a client, use IGMP snooping.


CGMP is a Cisco protocol that allows Catalyst switches to leverage IGMP information on Cisco routers to make Layer 2 forwarding decisions. CGMP is configured on the multicast routers and the Layer 2 switches. As a result, IP multicast traffic is delivered only to those Catalyst switchports with hosts that have requested the traffic. Switchports that have not explicitly requested the traffic will not receive it.

IP Multicast on the Catalyst 4500 Series Switch

The Catalyst 4000 family switch supports an ASIC-based Integrated Switching Engine that provides Ethernet bridging at Layer 2 and IP routing at Layer 3. Because the ASIC is specifically designed to forward packets, the Integrated Switching Engine hardware provides very high performance with ACLs and QoS enabled. At wire-speed, forwarding in hardware is significantly faster than the CPU subsystem software, which is designed to handle exception packets.

The Integrated Switching Engine hardware supports interfaces for inter-VLAN routing and switchports for Layer 2 bridging. It also provides a physical Layer 3 interface that can be configured to connect with a host, a switch, or a router.

Figure 29-2 shows a logical view of Layer 2 and Layer 3 forwarding in the Integrated Switching Engine hardware.

Figure 29-2 Logical View of Layer 2 and Layer 3 Forwarding in Hardware

This section contains the following subsections:

CEF, MFIB, and Layer 2 Forwarding

IP Multicast Tables

Hardware and Software Forwarding

Non-Reverse Path Forwarding Traffic

Multicast Fast Drop

Multicast Forwarding Information Base

S/M, 224/4

CEF, MFIB, and Layer 2 Forwarding

The implementation of IP multicast on the Catalyst 4000 family switch is an extension of centralized Cisco Express Forwarding (CEF). CEF extracts information from the unicast routing table, which is created by unicast routing protocols, such as BGP, OSPF, and EIGR and loads it into the hardware Forwarding Information Base (FIB). With the unicast routes in the FIB, when a route is changed in the upper-layer routing table, only one route needs to be changed in the hardware routing state. To forward unicast packets in hardware, the Integrated Switching Engine looks up source and destination routes in ternary content addressable memory (TCAM), takes the adjacency index from the hardware FIB, and gets the Layer 2 rewrite information and next-hop address from the hardware adjacency table.

The new Multicast Forwarding Information Base (MFIB) subsystem is the multicast analog of the unicast CEF. The MFIB subsystem extracts the multicast routes that PIM and IGMP create and refines them into a protocol-independent format for forwarding in hardware. The MFIB subsystem removes the protocol-specific information and leaves only the essential forwarding information. Each entry in the MFIB table consists of an (S,G) or (*,G) route, an input RPF VLAN, and a list of Layer 3 output interfaces. The MFIB subsystem, together with platform-dependent management software, loads this multicast routing information into the hardware FIB and hardware multicast expansion table (MET).

The Catalyst 4000 family switch performs Layer 3 routing and Layer 2 bridging at the same time. There can be multiple Layer 2 switchports on any VLAN interface. To determine the set of output switchports on which to forward a multicast packet, the Supervisor Engine III combines Layer 3 MFIB information with Layer 2 forwarding information and stores it in the hardware MET for packet replication.

Figure 29-3 shows a functional overview of how the Catalyst 4000 family switch combines unicast routing, multicast routing, and Layer 2 bridging information to forward in hardware.

Figure 29-3 Combining CEF, MFIB, and Layer 2 Forwarding Information in Hardware

Like the CEF unicast routes, the MFIB routes are Layer 3 and must be merged with the appropriate Layer 2 information. The following example shows an MFIB route:

(*,224.1.2.3)
RPF interface is Vlan3
Output Interfaces are:
Vlan 1
Vlan 2
 
   

The route (*,224.1.2.3) is loaded in the hardware FIB table and the list of output interfaces is loaded into the MET. A pointer to the list of output interfaces, the MET index, and the RPF interface are also loaded in the hardware FIB with the (*,224.1.2.3) route. With this information loaded in hardware, merging of the Layer 2 information can begin. For the output interfaces on VLAN1, the Integrated Switching Engine must send the packet to all switchports in VLAN1 that are in the spanning tree forwarding state. The same process applies to VLAN 2. To determine the set of switchports in VLAN 2, the Layer 2 Forwarding Table is used.

When the hardware routes a packet, in addition to sending it to all of the switchports on all output interfaces, the hardware also sends the packet to all switchports (other than the one it arrived on) in the input VLAN. For example, assume that VLAN 3 has two switchports in it, Gig 3/1 and Gig 3/2. If a host on Gig 3/1 sends a multicast packet, the host on Gig 3/2 might also need to receive the packet. To send a multicast packet to the host on Gig 3/2, all of the switchports in the ingress VLAN must be added to the portset that is loaded in the MET.

If VLAN 1 contains 1/1 and 1/2, VLAN 2 contains 2/1 and 2/2, and VLAN 3 contains 3/1 and 3/2, the MET chain for this route would contain these switchports: (1/1,1/2,2/1,2/2,3/1, and 3/2).

If IGMP snooping is on, the packet should not be forwarded to all output switchports on VLAN 2. The packet should be forwarded only to switchports where IGMP snooping has determined that there is either a group member or router. For example, if VLAN 1 had IGMP snooping enabled, and IGMP snooping determined that only port 1/2 had a group member on it, then the MET chain would contain these switchports: (1/1,1/2, 2/1, 2/2, 3/1, and 3/2).

IP Multicast Tables

Figure 29-4 shows some key data structures that the Catalyst 4000 family switch uses to forward IP multicast packets in hardware.

Figure 29-4 IP Multicast Tables and Protocols

The Integrated Switching Engine maintains the hardware FIB table to identify individual IP multicast routes. Each entry consists of a destination group IP address and an optional source IP address. Multicast traffic flows on primarily two types of routes: (S,G) and (*,G). The (S,G) routes flow from a source to a group based on the IP address of the multicast source and the IP address of the multicast group destination. Traffic on a (*,G) route flows from the PIM RP to all receivers of group G. Only sparse-mode groups use (*,G) routes. The Integrated Switching Engine hardware contains space for a total of 128,000 routes, which are shared by unicast routes, multicast routes, and multicast fast-drop entries.

Output interface lists are stored in the multicast expansion table (MET). The MET has room for up to 32,000 output interface lists. The MET resources are shared by both Layer 3 multicast routes and by Layer 2 multicast entries. The actual number of output interface lists available in hardware depends on the specific configuration. If the total number of multicast routes exceed 32,000, multicast packets might not be switched by the Integrated Switching Engine. They would be forwarded by the CPU subsystem at much slower speeds.

Hardware and Software Forwarding

The Integrated Switching Engine forwards the majority of packets in hardware at very high rates of speed. The CPU subsystem forwards exception packets in software. Statistical reports should show that the Integrated Switching Engine is forwarding the vast majority of packets in hardware.

Figure 29-5 shows a logical view of the hardware and software forwarding components.

Figure 29-5 Hardware and Software Forwarding Components

In the normal mode of operation, the Integrated Switching Engine performs inter-VLAN routing in hardware. The CPU subsystem supports generic routing encapsulation (GRE) tunnels for forwarding in software.

Replication is a particular type of forwarding where, instead of sending out one copy of the packet, the packet is replicated and multiple copies of the packet are sent out. At Layer 3, replication occurs only for multicast packets; unicast packets are never replicated to multiple Layer 3 interfaces. In IP multicasting, for each incoming IP multicast packet that is received, many replicas of the packet are sent out.

IP multicast packets can be transmitted on the following types of routes:

Hardware routes

Software routes

Partial routes

Hardware routes occur when the Integrated Switching Engine hardware forwards all replicas of a packet. Software routes occur when the CPU subsystem software forwards all replicas of a packet. Partial routes occur when the Integrated Switching Engine forwards some of the replicas in hardware and the CPU subsystem forwards some of the replicas in software.

Partial Routes


Note The conditions listed below cause the replicas to be forwarded by the CPU subsystem software, but the performance of the replicas that are forwarded in hardware is not affected.


The following conditions cause some replicas of a packet for a route to be forwarded by the CPU subsystem:

The switch is configured with the ip igmp join-group command as a member of the IP multicast group on the RPF interface of the multicast source.

The switch is the first-hop to the source in PIM sparse mode. In this case, the switch must send PIM-register messages to the RP.

Software Routes


Note If any one of the following conditions is configured on the RPF interface or the output interface, all replication of the output is performed in software.


The following conditions cause all replicas of a packet for a route to be forwarded by the CPU subsystem software:

The interface is configured with multicast helper.

The interface is a generic routing encapsulation (GRE) or Distance Vector Multicast Routing Protocol (DVMRP) tunnel.

The interface uses non-Advanced Research Products Agency (ARPA) encapsulation.

The following packets are always forwarded in software:

Packets sent to multicast groups that fall into the range 224.0.0.* (where * is in the range from 0 to 255). This range is used by routing protocols. Layer 3 switching supports all other multicast group addresses.

Packets with IP options.

Non-Reverse Path Forwarding Traffic

Traffic that fails an Reverse Path Forwarding (RPF) check is called non-RPF traffic. Non-RPF traffic is forwarded by the Integrated Switching Engine by filtering (persistently dropping) or rate limiting the non-RPF traffic.

In a redundant configuration where multiple Layer 3 switches or routers connect to the same LAN segment, only one device forwards the multicast traffic from the source to the receivers on the outgoing interfaces. Figure 29-6 shows how Non-RPF traffic can occur in a common network configuration.

Figure 29-6 Redundant Multicast Router Configuration in a Stub Network

In this kind of topology, only Router A, the PIM designated router (PIM DR), forwards data to the common VLAN. Router B receives the forwarded multicast traffic, but must drop this traffic because it has arrived on the wrong interface and fails the RPF check. Traffic that fails the RPF check is called non-RPF traffic.

Multicast Fast Drop

In IP multicast protocols, such as PIM-SM and PIM-DM, every (S,G) or (*,G) route has an incoming interface associated with it. This interface is referred to as the reverse path forwarding interface. In some cases, when a packet arrives on an interface other than the expected RPF interface, the packet must be forwarded to the CPU subsystem software to allow PIM to perform special protocol processing on the packet. One example of this special protocol processing that PIM performs is the PIM Assert protocol.

By default, the Integrated Switching Engine hardware sends all packets that arrive on a non-RPF interface to the CPU subsystem software. However, processing in software is not necessary in many cases, because these non-RPF packets are often not needed by the multicast routing protocols. The problem is that if no action is taken, the non-RPF packets that are sent to the software can overwhelm the CPU.

Use the ip mfib fastdrop command to enable or disable MFIB fast drops.

To prevent this from happening, the CPU subsystem software loads fast-drop entries in the hardware when it receives an RPF failed packet that is not needed by the PIM protocols running on the switch. A fast-drop entry is keyed by (S,G, incoming interface). Any packet matching a fast-drop entry is bridged in the ingress VLAN, but is not sent to the software, so the CPU subsystem software is not overloaded by processing these RPF failures unnecessarily.

Protocol events, such as a link going down or a change in the unicast routing table, can impact the set of packets that can safely be fast dropped. A packet that was correctly fast dropped before might, after a topology change, need to be forwarded to the CPU subsystem software so that PIM can process it. The CPU subsystem software handles flushing fast-drop entries in response to protocol events so that the PIM code in IOS can process all the necessary RPF failures.

The use of fast-drop entries in the hardware is critical in some common topologies because it is possible to have persistent RPF failures. Without the fast-drop entries, the CPU would be exhausted by RPF failed packets that it did not need to process.

Multicast Forwarding Information Base

The Multicast Forwarding Information Base (MFIB) subsystem supports IP multicast routing in the Integrated Switching Engine hardware on the Catalyst 4000 family switch. The MFIB logically resides between the IP multicast routing protocols in the CPU subsystem software (PIM, IGMP, MSDP, MBGP, and DVMRP) and the platform-specific code that manages IP multicast routing in hardware. The MFIB translates the routing table information created by the multicast routing protocols into a simplified format that can be efficiently processed and used for forwarding by the Integrated Switching Engine hardware.

To display the information in the multicast routing table, use the show ip mroute command. To display the MFIB table information, use the show ip mfib command.


Note In Supervisor Engine 6-E systems, the output of the show ip mfib command does not display any hardware counters.


The MFIB table contains a set of IP multicast routes. There are several types of IP multicast routes, including (S,G) and (*,G) routes. Each route in the MFIB table can have one or more optional flags associated with it. The route flags indicate how a packet that matches a route should be forwarded. For example, the Internal Copy (IC) flag on an MFIB route indicates that a process on the switch needs to receive a copy of the packet. The following flags can be associated with MFIB routes:

Internal Copy (IC) flag—set on a route when a process on the router needs to receive a copy of all packets matching the specified route

Signalling (S) flag—set on a route when a process needs to be notified when a packet matching the route is received; the expected behavior is that the protocol code updates the MFIB state in response to receiving a packet on a signalling interface

Connected (C) flag—-when set on an MFIB route, has the same meaning as the Signalling (S) flag, except that the C flag indicates that only packets sent by directly connected hosts to the route should be signalled to a protocol process

A route can also have a set of optional flags associated with one or more interfaces. For example, an (S,G) route with the flags on VLAN 1 indicates how packets arriving on VLAN 1 should be treated, and they also indicate whether packets matching the route should be forwarded onto VLAN 1. The per-interface flags supported in the MFIB include the following:

Accepting (A)—set on the interface that is known in multicast routing as the RPF interface. A packet that arrives on an interface that is marked as Accepting (A) is forwarded to all Forwarding (F) interfaces.

Forwarding (F)—used in conjunction with the Accepting (A) flag as described above. The set of Forwarding interfaces that form what is often referred to as the multicast "olist" or output interface list.

Signalling (S)—set on an interface when some multicast routing protocol process in IOS needs to be notified of packets arriving on that interface.

Not platform fast-switched (NP)—used in conjunction with the Forwarding (F) flag. A Forwarding interface is also marked as not platform fast-switched whenever that output interface cannot be fast switched by the platform. The NP flag is typically used when the Forwarding interface cannot be routed in hardware and requires software forwarding. For example, Catalyst 4000 family switch tunnel interfaces are not hardware switched, so they are marked with the NP flag. If there are any NP interfaces associated with a route, then for every packet arriving on an Accepting interface, one copy of that packet is sent to the software forwarding path for software replication to those interfaces that were not switched in hardware.


Note When PIM-SM routing is in use, the MFIB route might include an interface like in this example: PimTunnel [1.2.3.4]. This is a virtual interface that the MFIB subsystem creates to indicate that packets are being tunnelled to the specified destination address. A PimTunnel interface cannot be displayed with the normal show interface command.


S/M, 224/4

An (S/M, 224/4) entry is created in the MFIB for every multicast-enabled interface. This entry ensures that all packets sent by directly connected neighbors can be Register-encapsulated to the PIM-SM RP. Typically, only a small number of packets would be forwarded using the (S/M,224/4) route, until the (S,G) route is established by PIM-SM.

For example, on an interface with IP address 10.0.0.1 and netmask 255.0.0.0, a route would be created matching all IP multicast packets in which the source address is anything in the class A network 10. This route can be written in conventional subnet/masklength notation as (10/8,224/4). If an interface has multiple assigned IP addresses, then one route is created for each such IP address.

Unsupported Features

The following IP multicast features are not supported in this release:

Controlling the Transmission Rate to a Multicast Group

Load Splitting IP Multicast Traffic Across Equal-Cost Paths

Configuring IP Multicast Routing

The following sections describe IP multicast routing configuration tasks:

Default Configuration in IP Multicast Routing

Enabling IP Multicast Routing

Enabling PIM on an Interface

Enabling PIM-SSM mapping

For more detailed information on IP multicast routing, such as Auto-RP, PIM Version 2, and IP multicast static routes, refer to the Cisco IOS IP and IP Routing Configuration Guide, Cisco IOS Release 12.3.

Default Configuration in IP Multicast Routing

Table 29-1 shows the IP multicast default configuration.

Table 29-1 Default IP Multicast Configuration

Feature
Default Value

Rate limiting of RPF

Enabled globally

IP multicast routing

Disabled globally

Note When IP multicast routing is disabled, IP multicast traffic data packets are not forwarded by the Catalyst 4000 family switch. However, IP multicast control traffic will continue to be processed and forwarded. Therefore, IP multicast routes can remain in the routing table even if IP multicast routing is disabled.

PIM

Disabled on all interfaces

IGMP snooping

Enabled on all VLAN interfaces

Note If you disable IGMP snooping on an interface, all output ports are forwarded by the Integrated Switching Engine. When IGMP snooping is disabled on an input VLAN interface, multicast packets related to that interface are sent to all forwarding switchports in the VLAN.



Note Source-specific multicast and IGMP v3 are supported.


For more information about source-specific multicast with IGMPv3 and IGMP, see the following URL:

http://www.cisco.com/en/US/docs/ios/ipmulti/configuration/guide/imc_cfg_ssm.html

Enabling IP Multicast Routing

Enabling IP multicast routing allows the Catalyst 4000 family switch to forward multicast packets. To enable IP multicast routing on the router, perform this task in global configuration mode:

Command
Purpose

Switch(config)# ip multicast-routing

Enables IP multicast routing.


Enabling PIM on an Interface

Enabling PIM on an interface also enables IGMP operation on that interface. An interface can be configured to be in dense mode, sparse mode, or sparse-dense mode. The mode determines how the Layer 3 switch or router populates its multicast routing table and how the Layer 3 switch or router forwards multicast packets it receives from its directly connected LANs. You must enable PIM in one of these modes for an interface to perform IP multicast routing.

When the switch populates the multicast routing table, dense-mode interfaces are always added to the table. Sparse-mode interfaces are added to the table only when periodic join messages are received from downstream routers, or when there is a directly connected member on the interface. When forwarding from a LAN, sparse-mode operation occurs if there is an RP 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 receiver's first-hop router can send join messages toward the source to build a source-based distribution tree.

There is no default mode setting. By default, multicast routing is disabled on an interface.

Enabling Dense Mode

To configure PIM on an interface to be in dense mode, perform this task:

Command
Purpose

Switch(config-if)# ip pim dense-mode

Enables dense-mode PIM on the interface.


See the "PIM Dense Mode Example" section at the end of this chapter for an example of how to configure a PIM interface in dense mode.

Enabling Sparse Mode

To configure PIM on an interface to be in sparse mode, perform this task:

Command
Purpose

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

Enables sparse-mode PIM on the interface.


See the "PIM Sparse Mode Example" section at the end of this chapter for an example of how to configure a PIM interface in sparse mode.

Enabling Sparse-Dense Mode

When you enter either the ip pim sparse-mode or ip pim dense-mode command, 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. If you want to treat the group as a sparse group, and the interface is in sparse-dense mode, you must have an RP.

If you configure sparse-dense mode, the idea of sparseness or denseness is applied to the group on the switch, and the network manager should apply the same concept throughout the network.

Another benefit of sparse-dense mode is that Auto-RP information can be distributed in a dense-mode manner; yet, multicast groups for user groups can be used in a sparse-mode manner. Thus, 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 a multicast routing table's outgoing interface list when either of the following is true:

When there are members or DVMRP neighbors on the interface

When there are PIM neighbors and the group has not been pruned

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

When there are members or DVMRP neighbors on the interface

When an explicit join has been received by a PIM neighbor on the interface

To enable PIM to operate in the same mode as the group, perform this task:

Command
Purpose

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

Enables PIM to operate in sparse or dense mode, depending on the group.


Enabling PIM-SSM mapping

Catalyst 4500 series switch supports SSM mapping. This enables an SSM transition in cases where neither URD nor IGMP v3lite is available, or when supporting SSM on the end system is impossible or unwanted due to administrative or technical reasons. With SSM mapping, you can leverage SSM for video delivery to legacy set-top boxes (STBs) that do not support IGMPv3 or for applications that do not take advantage of the IGMPv3 host stack.

For more details, refer to this URL:

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtssmma.html

Monitoring and Maintaining IP Multicast Routing

You can remove all contents of a particular cache, table, or database. You also can display specific statistics. The following sections describe how to monitor and maintain IP multicast:

Displaying System and Network Statistics

Displaying the Multicast Routing Table

Displaying IP MFIB

Displaying IP MFIB Fast Drop

Displaying PIM Statistics

Clearing Tables and Databases

Displaying System and Network Statistics

You can display specific statistics, such as the contents of IP routing tables and databases. Information provided can be used to determine resource utilization and solve network problems. You can also display information about node reachability and discover the routing path your device's packets are taking through the network.

To display various routing statistics, you can perform any of these tasks:

Command
Purpose

Switch# ping [group-name | group-address]

Sends an ICMP Echo Request to a multicast group address.

Switch# show ip mroute [hostname | 
group_number]

Displays the contents of the IP multicast routing table.

Switch# show ip pim interface [type number] 
[count] 

Displays information about interfaces configured for PIM.

Switch# show ip interface 

Displays PIM information for all interfaces.


Displaying the Multicast Routing Table

The following is sample output from the show ip mroute command for a router operating in dense mode. This command displays the contents of the IP multicast FIB table for the multicast group named cbone-audio.

Switch# show ip mroute cbone-audio
 
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned
R - RP-bit set, F - Register flag, T - SPT-bit set
Timers: Uptime/Expires
Interface state: Interface, Next-Hop, State/Mode
 
(*, 224.0.255.1), uptime 0:57:31, expires 0:02:59, RP is 0.0.0.0, flags: DC
Incoming interface: Null, RPF neighbor 0.0.0.0, Dvmrp
Outgoing interface list:
    Ethernet0, Forward/Dense, 0:57:31/0:02:52
    Tunnel0, Forward/Dense, 0:56:55/0:01:28
 
(198.92.37.100/32, 224.0.255.1), uptime 20:20:00, expires 0:02:55, flags: C
Incoming interface: Tunnel0, RPF neighbor 10.20.37.33, Dvmrp
Outgoing interface list:
    Ethernet0, Forward/Dense, 20:20:00/0:02:52
 
   

The following is sample output from the show ip mroute command for a router operating in sparse mode:

Switch# show ip mroute
 
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned
R - RP-bit set, F - Register flag, T - SPT-bit set
Timers: Uptime/Expires
Interface state: Interface, Next-Hop, State/Mode
 
(*, 224.0.255.3), uptime 5:29:15, RP is 198.92.37.2, flags: SC
  Incoming interface: Tunnel0, RPF neighbor 10.3.35.1, Dvmrp
  Outgoing interface list:
    Ethernet0, Forward/Sparse, 5:29:15/0:02:57
 
(198.92.46.0/24, 224.0.255.3), uptime 5:29:15, expires 0:02:59, flags: C
  Incoming interface: Tunnel0, RPF neighbor 10.3.35.1
  Outgoing interface list:
    Ethernet0, Forward/Sparse, 5:29:15/0:02:57

Note Interface timers are not updated for hardware-forwarded packets. Entry timers are updated approximately every five seconds.


The following is sample output from the show ip mroute command with the summary keyword:

Switch# show ip mroute summary
 
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned
       R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT
Timers: Uptime/Expires
Interface state: Interface, Next-Hop, State/Mode
 
(*, 224.255.255.255), 2d16h/00:02:30, RP 171.69.10.13, flags: SJPC
 
(*, 224.2.127.253), 00:58:18/00:02:00, RP 171.69.10.13, flags: SJC
 
(*, 224.1.127.255), 00:58:21/00:02:03, RP 171.69.10.13, flags: SJC
 
(*, 224.2.127.254), 2d16h/00:00:00, RP 171.69.10.13, flags: SJCL
  (128.9.160.67/32, 224.2.127.254), 00:02:46/00:00:12, flags: CLJT
  (129.48.244.217/32, 224.2.127.254), 00:02:15/00:00:40, flags: CLJT
  (130.207.8.33/32, 224.2.127.254), 00:00:25/00:02:32, flags: CLJT
  (131.243.2.62/32, 224.2.127.254), 00:00:51/00:02:03, flags: CLJT
  (140.173.8.3/32, 224.2.127.254), 00:00:26/00:02:33, flags: CLJT
  (171.69.60.189/32, 224.2.127.254), 00:03:47/00:00:46, flags: CLJT
 

The following is sample output from the show ip mroute command with the active keyword:

Switch# show ip mroute active
 
Active IP Multicast Sources - sending >= 4 kbps
 
Group: 224.2.127.254, (sdr.cisco.com)
   Source: 146.137.28.69 (mbone.ipd.anl.gov)
     Rate: 1 pps/4 kbps(1sec), 4 kbps(last 1 secs), 4 kbps(life avg)
 
Group: 224.2.201.241, ACM 97
   Source: 130.129.52.160 (webcast3-e1.acm97.interop.net)
     Rate: 9 pps/93 kbps(1sec), 145 kbps(last 20 secs), 85 kbps(life avg)
 
Group: 224.2.207.215, ACM 97
   Source: 130.129.52.160 (webcast3-e1.acm97.interop.net)
     Rate: 3 pps/31 kbps(1sec), 63 kbps(last 19 secs), 65 kbps(life avg)
 
   

The following is sample output from the show ip mroute command with the count keyword:

Switch# show ip mroute count
 
IP Multicast Statistics - Group count: 8, Average sources per group: 9.87
Counts: Pkt Count/Pkts per second/Avg Pkt Size/Kilobits per second
 
Group: 224.255.255.255, Source count: 0, Group pkt count: 0
  RP-tree: 0/0/0/0
 
Group: 224.2.127.253, Source count: 0, Group pkt count: 0
  RP-tree: 0/0/0/0
 
Group: 224.1.127.255, Source count: 0, Group pkt count: 0
  RP-tree: 0/0/0/0
 
Group: 224.2.127.254, Source count: 9, Group pkt count: 14
  RP-tree: 0/0/0/0
  Source: 128.2.6.9/32, 2/0/796/0
  Source: 128.32.131.87/32, 1/0/616/0
  Source: 128.125.51.58/32, 1/0/412/0
  Source: 130.207.8.33/32, 1/0/936/0
  Source: 131.243.2.62/32, 1/0/750/0
  Source: 140.173.8.3/32, 1/0/660/0
  Source: 146.137.28.69/32, 1/0/584/0
  Source: 171.69.60.189/32, 4/0/447/0
  Source: 204.162.119.8/32, 2/0/834/0
 
Group: 224.0.1.40, Source count: 1, Group pkt count: 3606
  RP-tree: 0/0/0/0
  Source: 171.69.214.50/32, 3606/0/48/0, RPF Failed: 1203
 
Group: 224.2.201.241, Source count: 36, Group pkt count: 54152
  RP-tree: 7/0/108/0
  Source: 13.242.36.83/32, 99/0/123/0
  Source: 36.29.1.3/32, 71/0/110/0
  Source: 128.9.160.96/32, 505/1/106/0
  Source: 128.32.163.170/32, 661/1/88/0
  Source: 128.115.31.26/32, 192/0/118/0
  Source: 128.146.111.45/32, 500/0/87/0
  Source: 128.183.33.134/32, 248/0/119/0
  Source: 128.195.7.62/32, 527/0/118/0
  Source: 128.223.32.25/32, 554/0/105/0
  Source: 128.223.32.151/32, 551/1/125/0
  Source: 128.223.156.117/32, 535/1/114/0
  Source: 128.223.225.21/32, 582/0/114/0
  Source: 129.89.142.50/32, 78/0/127/0
  Source: 129.99.50.14/32, 526/0/118/0
  Source: 130.129.0.13/32, 522/0/95/0
  Source: 130.129.52.160/32, 40839/16/920/161
  Source: 130.129.52.161/32, 476/0/97/0
  Source: 130.221.224.10/32, 456/0/113/0
  Source: 132.146.32.108/32, 9/1/112/0

Note Multicast route byte and packet statistics are supported only for the first 1024 multicast routes. Output interface statistics are not maintained.


Displaying IP MFIB

You can display all routes in the MFIB, including routes that might not exist directly in the upper-layer routing protocol database but that are used to accelerate fast switching. These routes appear in the MFIB, even if dense-mode forwarding is in use.

To display various MFIB routing routes, perform one of these tasks:

Command
Purpose

Switch# show ip mfib

Displays the (S,G) and (*,G) routes that are used for packet forwarding. Displays counts for fast, slow, and partially-switched packets for every multicast route.

Switch# show ip mfib all

Displays all routes in the MFIB, including routes that may not exist directly in the upper-layer routing protocol database, but that are used to accelerate fast switching.These routes include the (S/M,224/4) routes.

Switch# show ip mfib log [n]

Displays a log of the most recent n MFIB related events, most recent first.

Switch# show ip mfib counters

Displays counts of MFIB related events. Only non-zero counters are shown.


The following is sample output from the show ip mfib command.

IP Multicast Forwarding Information Base
Entry Flags: C - Directly Connected, S - Signal,
             IC - Internal Copy
Interface Flags: A - Accept, F - Forward, S - Signal,
             NP - Not platform switched
Packets: Fast/Partial/Slow Bytes: Fast/Partial/Slow:
(171.69.10.13, 224.0.1.40), flags (IC)
   Packets: 2292/2292/0, Bytes: 518803/0/518803
   Vlan7 (A)
   Vlan100 (F NS)
   Vlan105 (F NS)
(*, 224.0.1.60), flags ()
   Packets: 2292/0/0, Bytes: 518803/0/0
   Vlan7 (A NS)
(*, 224.0.1.75), flags ()
   Vlan7 (A NS)
(10.34.2.92, 239.192.128.80), flags ()
   Packets: 24579/100/0, 2113788/15000/0 bytes
   Vlan7 (F NS)
   Vlan100 (A)
(*, 239.193.100.70), flags ()
   Packets: 1/0/0, 1500/0/0 bytes
   Vlan7 (A)
..
 
   

The fast-switched packet count represents the number of packets that were switched in hardware on the corresponding route.

The partially switched packet counter represents the number of times that a fast-switched packet was also copied to the CPU for software processing or for forwarding to one or more non-platform switched interfaces (such as a PimTunnel interface).

The slow-switched packet count represents the number of packets that were switched completely in software on the corresponding route.

Displaying IP MFIB Fast Drop


Note Supervisor Engine 6-E does not support the show ip mfib fastdrop command.


To display fast-drop entries, perform this task:

Command
Purpose

Switch# show ip mfib fastdrop

Displays all currently active fast-drop entries and indicates whether fastdrop is enabled.


The following is sample output from the show ip mfib fastdrop command.

Switch> show ip mfib fastdrop
MFIB fastdrop is enabled.
MFIB fast-dropped flows:
(10.0.0.1, 224.1.2.3, Vlan9 ) 00:01:32
(10.1.0.2, 224.1.2.3, Vlan9 ) 00:02:30
(1.2.3.4, 225.6.7.8, Vlan3) 00:01:50
 
   

The full (S,G) flow and the ingress interface on which incoming packets are dropped is shown. The timestamp indicates the age of the entry.

Displaying PIM Statistics

The following is sample output from the show ip pim interface command:

Switch# show ip pim interface
 
Address          Interface          Mode    Neighbor  Query     DR
                                            Count     Interval
198.92.37.6      Ethernet0          Dense   2         30        198.92.37.33
198.92.36.129    Ethernet1          Dense   2         30        198.92.36.131
10.1.37.2        Tunnel0            Dense   1         30        0.0.0.0
 
   

The following is sample output from the show ip pim interface command with a count:

Switch# show ip pim interface count
 
Address          Interface          FS  Mpackets In/Out
171.69.121.35    Ethernet0          *   548305239/13744856
171.69.121.35    Serial0.33         *   8256/67052912
198.92.12.73     Serial0.1719       *   219444/862191
 
   

The following is sample output from the show ip pim interface command with a count when IP multicast is enabled. The example lists the PIM interfaces that are fast-switched and process-switched, and the packet counts for these. The H is added to interfaces where IP multicast is enabled.

Switch# show ip pim interface count
 
States: FS - Fast Switched, H - Hardware Switched
Address          Interface          FS  Mpackets In/Out
192.1.10.2       Vlan10             * H 40886/0
192.1.11.2       Vlan11             * H 0/40554
192.1.12.2       Vlan12             * H 0/40554
192.1.23.2       Vlan23             *   0/0
192.1.24.2       Vlan24             *   0/0

Clearing Tables and Databases

You can remove all contents of a particular cache, table, or database. Clearing a cache, table, or database might be necessary when the contents of the particular structure have become, or are suspected to be, invalid.

To clear IP multicast caches, tables, and databases, perform one of these tasks:

Command
Purpose
Switch# clear ip mroute 

Deletes entries from the IP routing table.

Switch# clear ip mfib counters 

Deletes all per-route and global MFIB counters.

Switch# clear ip mfib fastdrop

Deletes all fast-drop entries.



Note IP multicast routes can be regenerated in response to protocol events and as data packets arrive.


Configuration Examples

The following sections provide IP multicast routing configuration examples:

PIM Dense Mode Example

PIM Sparse Mode Example

BSR Configuration Example

PIM Dense Mode Example

This example is a configuration of dense-mode PIM on an Ethernet interface:

ip multicast-routing
interface ethernet 0
 ip pim dense-mode

PIM Sparse Mode Example

This example is a configuration of sparse-mode PIM. The RP router is the router with the address 10.8.0.20.

ip multicast-routing
 ip pim rp-address 10.8.0.20 1
interface ethernet 1
 ip pim sparse-mode

BSR Configuration Example

This example is a configuration of a candidate BSR, which also happens to be a candidate RP:

version 11.3
!
ip multicast-routing
!
interface Ethernet0
 ip address 171.69.62.35 255.255.255.240
!
interface Ethernet1
 ip address 172.21.24.18 255.255.255.248
 ip pim sparse-dense-mode
!
interface Ethernet2
 ip address 172.21.24.12 255.255.255.248
 ip pim sparse-dense-mode
!
router ospf 1
 network 172.21.24.8 0.0.0.7 area 1
 network 172.21.24.16 0.0.0.7 area 1
!
ip pim bsr-candidate Ethernet2 30 10
ip pim rp-candidate Ethernet2 group-list 5
access-list 5 permit 239.255.2.0 0.0.0.255