Each multicast routing protocol has its own routing table. Multicast routing information in routing entries generated by the multicast routing protocols and statically configured multicast routing entries are summarized in a set of (S, G) and (*, G) entries. All the (S, G) and (*, G) entries form a general multicast routing table. The optimal multicast routing entries in the general multicast routing table are added to the multicast forwarding table to guide multicast data forwarding.

RPF check mechanism

A multicast routing protocol uses reverse path forwarding (RPF) check to ensure the multicast data delivery along the correct path and to avoid data loops.

RPF check process

A multicast device performs the RPF check on a multicast packet as follows:

1. Chooses an optimal route back to the packet source separately from the unicast, MBGP, and static multicast routing tables.

The term "packet source" means different things in different situations:

¡ For a packet that travels along the SPT, the packet source is the multicast source.

¡ For a packet that travels along the RPT, the packet source is the RP.

¡ For a bootstrap message originated from the BSR, the packet source is the BSR.

For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see "Configuring PIM."

2. Selects one of the three optimal routes as the RPF route as follows:

¡ If the device uses the longest prefix match principle, the route with the highest subnet mask becomes the RPF route. If the routes have the same mask, the route with the highest route preference becomes the RPF route. If the routes have the same route preference, the unicast route becomes the RPF route. If equal cost routes exist, the route with the highest next hop IP address becomes the RPF route.

For more information about the route preference, see Layer 3—IP Routing Configuration Guide.

¡ If the device does not use the longest prefix match principle, the route with the highest route preference becomes the RPF route. If the routes have the same preference, the unicast route becomes the RPF route. If equal cost routes exist, the route with the highest next hop IP address becomes the RPF route.

The RPF route contains the RPF interface and RPF neighbor information.

¡ If the RPF route is a unicast route or MBGP route, the outgoing interface is the RPF interface and the next hop is the RPF neighbor.

¡ If the RPF route is a static multicast route, the RPF interface and RPF neighbor are specified in the route.

3. Determines whether the packet arrived at the RPF interface.

¡ If the packet arrived at the RPF interface, the RPF check succeeds and the packet is forwarded.

¡ If the packet arrived at the non-RPF interface, the RPF check fails and the packet is discarded.

RPF check implementation in multicast

Implementing an RPF check on each received multicast packet brings a big burden to the device. The use of a multicast forwarding table is the solution to this issue. When the device creates a multicast forwarding entry for an (S, G) packet, it sets the RPF interface of the packet as the incoming interface of the (S, G) entry. After the device receives another (S, G) packet, it looks up the multicast forwarding table for a matching (S, G) entry.

· If no match is found, the device first determines the RPF route back to the packet source and the RPF interface. Then, it creates a forwarding entry with the RPF interface as the incoming interface and makes the following judgments:

¡ If the receiving interface is the RPF interface, the RPF check succeeds and the device forwards the packet out of all the outgoing interfaces.

¡ If the receiving interface is not the RPF interface, the RPF check fails and the device discards the packet.

· If a match is found and the matching forwarding entry contains the receiving interface, the device forwards the packet out of all the outgoing interfaces.

· If a match is found but the matching forwarding entry does not contain the receiving interface, the device determines the RPF route back to the packet source. Then, the device performs one of the following actions:

¡ If the RPF interface is the incoming interface, it means that the forwarding entry is correct but the packet traveled along a wrong path. The packet fails the RPF check, and the device discards the packet.

¡ If the RPF interface is not the incoming interface, it means that the forwarding entry has expired. The device replaces the incoming interface with the RPF interface and matches the receiving interface against the RPF interface. If the receiving interface is the RPF interface, the device forwards the packet out of all outgoing interfaces. Otherwise, it discards the packet.

Figure 1 RPF check process

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As shown in Figure 1, assume that unicast routes are available on the network, MBGP is not configured, and no static multicast routes have been configured on Device C. Multicast packets travel along the SPT from the multicast source to the receivers. The multicast forwarding table on Device C contains the (S, G) entry, with Port A as the incoming interface.

· If a multicast packet arrives at Device C on Port A, the receiving interface is the incoming interface of the (S, G) entry. Device C forwards the packet out of all outgoing interfaces.

· If a multicast packet arrives at Device C on Port B, the receiving interface is not the incoming interface of the (S, G) entry. Device C searches its unicast routing table and finds that the outgoing interface to the source (the RPF interface) is Port A. In this case, the (S, G) entry is correct, but the packet traveled along a wrong path. The packet fails the RPF check and Device C discards the packet.

Usages of static multicast routes

A static multicast route can change an RPF route or create an RPF route.

Changing an RPF route

Typically, the topology structure of a multicast network is the same as that of a unicast network, and multicast traffic follows the same transmission path as unicast traffic does. You can configure a static multicast route for a multicast source to change the RPF route. As a result, the device creates a transmission path for multicast traffic that is different from the transmission path for unicast traffic.

Figure 2 Changing an RPF route

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As shown in Figure 2, when no static multicast route is configured, Device C's RPF neighbor on the path back to the source is Device A. The multicast data from the source travels through Device A to Device C. You can configure a static multicast route on Device C and specify Device B as Device C's RPF neighbor on the path back to the source. The multicast data from the source travels along the path: Device A to Device B and then to Device C.

Creating an RPF route

When a unicast route is blocked, multicast forwarding might be stopped due to lack of an RPF route. You can configure a static multicast route to create an RPF route. In this way, a multicast routing entry is created to guide multicast forwarding.

Figure 3 Creating an RPF route

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As shown in Figure 3, the RIP domain and the OSPF domain are unicast isolated from each other. For the receiver hosts in the OSPF domain to receive multicast packets from the multicast source in the RIP domain, you must configure Device C and Device D as follows:

· On Device C, configure a static multicast route for the multicast source and specify Device B as the RPF neighbor.

· On Device D, configure a static multicast route for the multicast source and specify Device C as the RPF neighbor.

Multicast forwarding across unicast subnets

Multicast data transmission over a 6to4 or ISATAP tunnel is not supported in the current software version.

Devices forward the multicast data from a multicast source hop by hop along the forwarding tree, but some devices might not support multicast protocols in a network. When the multicast data is forwarded to a device that does not support IP multicast, the forwarding path is blocked. In this case, you can enable multicast forwarding across two unicast subnets by establishing a tunnel between the devices at the edges of the two unicast subnets.

Figure 4 Multicast data transmission through a tunnel

As shown in Figure 4, a tunnel is established between Device A and Device B. Device A encapsulates the multicast data in unicast IP packets, and forwards them to Device B across the tunnel through unicast devices. Then, Device B strips off the unicast IP header and continues to forward the multicast data to the receiver.

To use this tunnel only for multicast traffic, configure the tunnel as the outgoing interface only for multicast routes.

Restrictions and guidelines: Multicast routing and forwarding configuration

The device can route and forward multicast data only through the primary IP addresses of interfaces, rather than their secondary addresses or unnumbered IP addresses. For more information about primary and secondary IP addresses, and IP unnumbered, see Layer 3—IP Services Configuration Guide.

Multicast routing and forwarding tasks at a glance

To configure multicast routing and forwarding, perform the following tasks:

1. Enabling IP multicast routing

2. (Optional.) Configuring static multicast routes

3. (Optional.) Specifying the longest prefix match principle

4. (Optional.) Configuring multicast load splitting

5. (Optional.) Configuring a multicast forwarding boundary

6. (Optional.) Configuring RPF check failure processing

¡ Configuring the device to flood RPF-check-failed multicast data packets in all VLANs

¡ Configuring the device to send RPF-check-failed multicast data packets to the CPU

7. (Optional.) Setting the maximum number of cached unknown multicast packets

8. (Optional.) Configuring multicast FRR

¡ Setting the multicast FRR mode

¡ Setting the primary/backup link monitoring interval

¡ Configuring traffic switchback from the backup link to the primary link

9. (Optional.) Configuring PIM entry limits

¡ Configuring global PIM entry limits

¡ Configuring PIM entry limits for the public network or a VPN instance

10. (Optional.) Enabling SNMP notifications for multicast routing and forwarding

Prerequisites for multicast routing and forwarding

Before you configure multicast routing and forwarding, configure a unicast routing protocol so that all devices in the domain can interoperate at the network layer.

Enabling IP multicast routing

About this task

Enable IP multicast routing before you configure any Layer 3 multicast functionality on the public network or VPN instance.

Procedure

1. Enter system view.

system-view

2. Enable IP multicast routing and enter MRIB view.

multicast routing [ vpn-instance vpn-instance-name ]

By default, IP multicast routing is disabled.

Configuring static multicast routes

About this task

To configure a static multicast route for a multicast source, you can specify an RPF interface or an RPF neighbor for the multicast traffic from that source.

Restrictions and guidelines

Static multicast routes take effect only on the multicast devices on which they are configured, and will not be advertised throughout the network or redistributed to other devices.

If you specify an outgoing interface configured with IP unnumbered, the static multicast route does not take effect.

Procedure

1. Enter system view.

system-view

2. Configure a static multicast route.

ip rpf-route-static [ vpn-instance vpn-instance-name ] source-address { mask-length | mask } { rpf-nbr-address | interface-type interface-number } [ preference preference ] [ description text ]

3. (Optional.) Delete all static multicast routes.

delete ip rpf-route-static [ vpn-instance vpn-instance-name ]

You can use the undo ip rpf-route-static command to delete a specific static multicast route or use the delete ip rpf-route-static command to delete all static multicast routes.

Specifying the longest prefix match principle

About this task

You can enable the device to use the longest prefix match principle for RPF route selection. For more information about RPF route selection, see "RPF check process."

Procedure

1. Enter system view.

system-view

2. Enter MRIB view.

multicast routing [ vpn-instance vpn-instance-name ]

3. Specify the longest prefix match principle.

longest-match

By default, the route preference principle is used.

Configuring multicast load splitting

About this task

You can enable the device to split multiple data flows on a per-source basis or on a per-source-and-group basis. This optimizes the traffic delivery.

Procedure

1. Enter system view.

system-view

2. Enter MRIB view.

multicast routing [ vpn-instance vpn-instance-name ]

3. Configure multicast load splitting.

load-splitting { balance-ecmp | balance-ucmp | ecmp | source | source-group | ucmp }

By default, multicast load splitting is disabled.

Configuring a multicast forwarding boundary

About this task

You can configure an interface as a multicast forwarding boundary for a multicast group range. The interface cannot receive or forward multicast packets for the group range.

Restrictions and guidelines

You do not need to enable IP multicast before this configuration.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the interface as a multicast forwarding boundary for a multicast group range.

multicast boundary group-address { mask-length | mask }

By default, an interface is not a multicast forwarding boundary.

Configuring RPF check failure processing

Configuring the device to flood RPF-check-failed multicast data packets in all VLANs

About this task

In some networks, multicast receivers might exist in VLANs to which RPF-check-failed multicast data packets belong. For the receivers to receive the packets, you can configure the device to flood the packets in all VLANs.

Restrictions and guidelines

You do not need to enable IP multicast before this configuration.

Procedure

1. Enter system view.

system-view

2. Configure the device to flood RPF-check-failed multicast data packets in all VLANs.

multicast rpf-fail-pkt flooding

By default, RPF-check-failed multicast data packets are not flooded in all VLANs.

3. Return to user view.

quit

4. Clear all multicast forwarding entries.

reset multicast [ vpn-instance vpn-instance-name ] forwarding-table all

The multicast rpf-fail-pkt flooding command takes effect only after you perform this step.

Configuring the device to send RPF-check-failed multicast data packets to the CPU

About this task

In the following cases, multicast data packets that fail the RPF check must be sent to the CPU:

· If a multicast data packet arrives on an outgoing interface of the corresponding multicast forwarding entry, the packet fails the RPF check. Such packets must be delivered to the CPU to trigger the assert mechanism to prune the unwanted branch. For more information about the assert mechanism, DR, and RPT-to-SPT switchover, see "Configuring PIM."

· Assume that the SPT and RPT have different incoming interfaces on the receiver-side DR in a PIM-SM domain. Before the switchover to SPT finishes, the RPF interface of the route on the DR to the multicast source remains as the RPT incoming interface. The multicast packets that travel along the SPT will fail the RPF check and be discarded. If the RPT is pruned at this moment, the multicast service is instantaneously interrupted.

To avoid this problem, you can configure the device to send the packets that travel along the SPT and fail the RPF check to the CPU. When the packets arrive at the CPU, the system determines whether the packets are expected. If they are expected, the device initiates an RPT prune.

Restrictions and guidelines

You do not need to enable IP multicast before this configuration.

Procedure

1. Enter system view.

system-view

2. Configure the device to send RPF-check-failed multicast data packets to the CPU.

multicast rpf-fail-pkt trap-to-cpu

By default, RPF-check-failed multicast data packets are not sent to the CPU.

3. Return to user view.

quit

4. Clear all multicast forwarding entries.

reset multicast[ vpn-instance vpn-instance-name ] forwarding-table all

The multicast rpf-fail-pkt trap-to-cpu command takes effect only after you perform this step.

Setting the maximum number of cached unknown multicast packets

About this task

The device caches a multicast packet for a period of time if no matching multicast forwarding entry is found for the packet. If a multicast forwarding entry is created for the packet within the time period, the device forwards the packet. This mechanism prevents the device from mistakenly dropping multicast packets when the multicast forwarding entries for these packets are to be established.

You can set the maximum number of unknown multicast packets that can be cached for an (S, G) entry, in total, or both.

Restrictions and guidelines

As a best practice, set the value in the multicast forwarding-table cache-unknown total command to be far greater than the value in the multicast forwarding-table cache-unknown per-entry command.

Procedure

1. Enter system view.

system-view

2. Set the maximum number of unknown multicast packets that can be cached for an (S, G) entry.

multicast forwarding-table cache-unknown per-entry per-entry-limit

By default, the device can cache only one unknown multicast packet for an (S, G) entry.

3. Set the maximum number of unknown multicast packets that can be cached in total.

multicast forwarding-table cache-unknown total total-limit

By default, the device can cache 1024 unknown multicast packets in total.

Configuring multicast FRR

Setting the multicast FRR mode

About this task

With multicast FRR enabled, the device will add a primary incoming interface and a backup incoming interface for each (S, G) entry during entry creation. It will periodically monitor multicast traffic on the primary and backup incoming interfaces of all entries. If no multicast traffic is detected on the primary incoming interface, the device determines that the primary incoming interface fails and uses the backup incoming interface for multicast forwarding.

Multicast FRR supports the following modes to monitor multicast traffic:

· By-entry—In this mode, multicast FRR periodically monitors multicast traffic on primary and backup incoming interfaces by (S, G) entry.

· By-incoming interface—In this mode, multicast FRR periodically monitors multicast traffic for different (S, G) entries by pair of primary and backup incoming interfaces.

Restrictions and guidelines

In the current software version, only PIM supports multicast FRR. For more information about PIM FRR, see "Configuring PIM."

Proceudre

1. Enter system view.

system-view

2. Set the multicast FRR mode.

multicast frr mode [ by-entry | by-iif ]

By default, the multicast FRR mode is by-entry.

Setting the primary/backup link monitoring interval

About this task

To speed up the convergence of multicast services, you can enable multicast FRR on the receiver-side device. With multicast FRR enabled, the device will add a primary incoming interface and a backup incoming interface for each (S, G) entry during entry creation. It will periodically monitor multicast traffic on the primary and backup incoming interfaces of all entries. If no multicast traffic is detected on the primary incoming interface, the device determines that the primary incoming interface fails and uses the backup incoming interface for multicast forwarding. You can set the internal at which multicast FRR monitors the states of the primary and backup links.

Restrictions and guidelines

Before performing this task, execute the rpf-frr enable or c-multicast frr command. For more information about the commands, see Multicast Command Reference.

As a best practice to prevent the CPU from being overloaded, set the monitoring interval to a larger value if there are many multicast entries. As a best practice to prevent the device from determining link failures mistakenly when the multicast traffic rate is small, also set the monitoring interval to a larger value if there are many multicast entries.

Proceudre

1. Enter system view.

system-view

2. Set the primary/backup link monitoring interval.

multicast frr monitor cycle monitor-time

The default setting is 200 milliseconds.

Configuring traffic switchback from the backup link to the primary link

About this task

With multicast FRR enabled, the device accepts the multicast traffic from the backup link if the primary fails. You can configure whether to switch the traffic back to the primary link after the primary link recovers.

Restrictions and guidelines

Before performing this task, execute the rpf-frr enable or c-multicast frr command. For more information about the commands, see Multicast Command Reference.

To prevent multicast traffic from being switched back before the multicast entries are created for the primary link, do not set too short a wait-to-restore (WTR) time.

Multicast packets might be lost or duplicate multicast packets might exist during a traffic switchback. As a best practice, do not configure traffic switchback for multicast services requiring high reliability.

Proceudre

1. Enter system view.

system-view

2. Configure traffic switchback from the backup link to the primary link.

multicast frr wtr { wtr-time | disable }

The default setting is 600 seconds.

Configuring PIM entry limits

Configuring global PIM entry limits

About this task

When an illegal user launches an attack by using multicast data or protocol (IGMP or PIM) packets, a large number of multicast routing entries might be generated, causing high memory or CPU usage.

Perform this task to protect the device by limiting the number of PIM entries.

Restrictions and guidelines

When the number of global PIM entries reaches the limit, new PIM entries cannot be created and a log message is generated.

Static (*,G) entries, static (S,G) entries, and ASM default group entries are not affected by this function.

Proceudre

1. Enter system view.

system-view

2. Configure global PIM entry limits.

multicast global limit pim sm { source-group-number | star-group-number } limit-count [ alarm-threshold upper-limit upper-limit lower-limit lower-limit ]

By default, no global PIM entry limits are configured.

Configuring PIM entry limits for the public network or a VPN instance

About this task

When an illegal user launches an attack by using multicast data or protocol (IGMP or PIM) packets, a large number of multicast routing entries might be generated, causing high memory or CPU usage.

Perform this task to protect the device by limiting the number of PIM entries for the public network or a VPN instance.

Restrictions and guidelines

When the number of global PIM entries reaches the limit, new PIM entries cannot be created and a log message is generated.

Static (*,G) entries, static (S,G) entries, and ASM default group entries are not affected by this function.

Proceudre

1. Enter system view.

system-view

2. Enter MRIB view.

multicast routing [ vpn-instance vpn-instance-name ]

3. Configure PIM entry limits.

multicast limit pim sm { source-group-number | star-group-number } limit-count [ alarm-threshold upper-limit upper-limit lower-limit lower-limit ]

By default, no PIM entry limits are configured.

Enabling SNMP notifications for multicast routing and forwarding

About this task

To report critical multicast routing and forwarding events to an NMS, enable SNMP notifications for multicast routing and forwarding. For multicast routing and forwarding event notifications to be sent correctly, you must also configure SNMP on the device. For more information about SNMP configuration, see Network Management and Monitoring Configuration Guide.

Procedure

1. Enter system view.

system-view

2. Enable SNMP notifications for multicast routing and forwarding.

snmp-agent trap enable mrib [ entry-exceed | entry-exceed-clear ] *

By default, SNMP notifications for multicast routing and forwarding are enabled.

Display and maintenance commands for multicast routing and forwarding

CAUTION:

The reset commands might cause multicast data transmission failures.

Execute display commands in any view and reset commands in user view.

Task	Command
Display information about the interfaces maintained by the MRIB.	display mrib [ vpn-instance vpn-instance-name ] interface [ interface-type interface-number ]
Display multicast boundary information.	display multicast [ vpn-instance vpn-instance-name ] boundary [ group-address [ mask-length \| mask ] ] [ interface interface-type interface-number ]
Display multicast fast forwarding entries.	In standalone mode: display multicast [ vpn-instance vpn-instance-name ] fast-forwarding cache [ source-address \| group-address ] * [ slot slot-number [ cpu cpu-number ] ] In IRF mode: display multicast [ vpn-instance vpn-instance-name ] fast-forwarding cache [ source-address \| group-address ] * [ chassis chassis-number slot slot-number [ cpu cpu-number ] ]
Display statistics for multicast forwarding events.	In standalone mode: display multicast [ vpn-instance vpn-instance-name ] forwarding event [ slot slot-number [ cpu cpu-number ] ] In IRF mode: display multicast [ vpn-instance vpn-instance-name ] forwarding event [ chassis chassis-number slot slot-number [ cpu cpu-number ] ]
Display multicast forwarding entries.	In standalone mode: display multicast [ vpn-instance vpn-instance-name ] forwarding-table [ source-address [ mask { mask-length \| mask } ] \| group-address [ mask { mask-length \| mask } ] \| incoming-interface interface-type interface-number \| outgoing-interface { exclude \| include \| match } interface-type interface-number \| slot slot-number [ cpu cpu-number ] \| statistics ] * In IRF mode: display multicast [ vpn-instance vpn-instance-name ] forwarding-table [ source-address [ mask { mask-length \| mask } ] \| group-address [ mask { mask-length \| mask } ] \| incoming-interface interface-type interface-number \| outgoing-interface { exclude \| include \| match } interface-type interface-number \| chassis chassis-number slot slot-number [ cpu cpu-number ] \| statistics ] *
Display multicast routing entries.	display multicast [ vpn-instance vpn-instance-name ] routing-table [ source-address [ mask { mask-length \| mask } ] \| group-address [ mask { mask-length \| mask } ] \| incoming-interface interface-type interface-number \| outgoing-interface { exclude \| include \| match } interface-type interface-number ] *
Display static multicast routing entries.	display multicast [ vpn-instance vpn-instance-name ] routing-table static [ source-address { mask-length \| mask } ]
Display RPF information for a multicast source.	display multicast [ vpn-instance vpn-instance-name ] rpf-info source-address [ group-address ]
Display the configuration and statistics for global PIM entry limits.	display multicast global pim sm statistics
Display the configuration and statistics for PIM entry limits for the public network or a VPN instance.	display multicast [ vpn-instance vpn-instance-name ] pim sm statistics
Display multicast traffic statistics.	display multicast flow-statistic source source-address group group-address interface interface-type interface-number [ s-vlan svlan-id [ c-vlan cvlan-id ] ] { inbound \| outbound } This command is available only for the following cards: CEPC: CEPC-XP4LX, CEPC-XP24LX, CEPC-XP48RX, CEPC-CP4RX, CEPC-CP4RX-L, CEPC-CQ8L, CEPC-CQ16L1, CEPC-DQ2L1-G CSPEX: CSPEX-1304X, CSPEX-1304S, CSPEX-1404X, CSPEX-1404S, CSPEX-1502X, CSPEX-1504X, CSPEX-1504S, CSPEX-1602X, CSPEX-1804X, CSPEX-1512X, CSPEX-1612X, CSPEX-1812X, CSPEX-1802XB, CSPEX-1802X, CSPEX-1812X-E, CSPEX-2304X-G, CSPEX-2304X-LG, CSPEX-2612X-E SPE: RX-SPE200, RX-SPE200-E
Clear multicast fast forwarding entries.	In standalone mode: reset multicast [ vpn-instance vpn-instance-name ] fast-forwarding cache { { source-address \| group-address } * \| all } [ slot slot-number [ cpu cpu-number ] ] In IRF mode: reset multicast [ vpn-instance vpn-instance-name ] fast-forwarding cache { { source-address \| group-address } * \| all } [ chassis chassis-number slot slot-number [ cpu cpu-number ] ]
Clear statistics for multicast forwarding events.	reset multicast [ vpn-instance vpn-instance-name ] forwarding event
Clear multicast forwarding entries.	reset multicast [ vpn-instance vpn-instance-name ] forwarding-table { { source-address [ mask { mask-length \| mask } ] \| group-address [ mask { mask-length \| mask } ] \| incoming-interface { interface-type interface-number } } * \| all }
Clear multicast routing entries.	reset multicast [ vpn-instance vpn-instance-name ] routing-table { { source-address [ mask { mask-length \| mask } ] \| group-address [ mask { mask-length \| mask } ] \| incoming-interface interface-type interface-number } * \| all }

NOTE:

· When you clear a multicast routing entry, the associated multicast forwarding entry is also cleared.

· When you clear a multicast forwarding entry, the associated multicast routing entry is also cleared.

Multicast routing and forwarding configuration examples

Example: Changing an RPF route

Network configuration

As shown in Figure 5:

· PIM-DM runs on the network.

· All routers on the network support multicast.

· Router A, Router B, and Router C run OSPF.

· Typically, the receiver host can receive the multicast data from the source through the path: Router A to Router B, which is the same as the unicast route.

Configure the routers so that the multicast data from the source travels to the receiver along the following path: Router A to Router C to Router B. This path is different from the unicast route.

Figure 5 Network diagram

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Procedure

1. Assign an IP address and subnet mask for each interface, as shown in Figure 5. (Details not shown.)

2. Configure OSPF on the routers in the PIM-DM domain. (Details not shown.)

3. Enable IP multicast routing, and enable IGMP and PIM-DM:

# On Router B, enable IP multicast routing.

<RouterB> system-view

[RouterB] multicast routing

[RouterB-mrib] quit

# Enable IGMP on the receiver-side interface Ten-GigabitEthernet 3/1/1.

[RouterB] interface ten-gigabitethernet 3/1/1

[RouterB-Ten-GigabitEthernet3/1/1] igmp enable

[RouterB-Ten-GigabitEthernet3/1/1] quit

# Enable PIM-DM on the other interfaces.

[RouterB] interface ten-gigabitethernet 3/1/2

[RouterB-Ten-GigabitEthernet3/1/2] pim dm

[RouterB-Ten-GigabitEthernet3/1/2] quit

[RouterB] interface ten-gigabitethernet 3/1/3

[RouterB-Ten-GigabitEthernet3/1/3] pim dm

[RouterB-Ten-GigabitEthernet3/1/3] quit

# On Router A, enable IP multicast routing.

<RouterA> system-view

[RouterA] multicast routing

[RouterA-mrib] quit

# Enable PIM-DM on each interface.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] pim dm

[RouterA-Ten-GigabitEthernet3/1/1] quit

[RouterA] interface ten-gigabitethernet 3/1/2

[RouterA-Ten-GigabitEthernet3/1/2] pim dm

[RouterA-Ten-GigabitEthernet3/1/2] quit

[RouterA] interface ten-gigabitethernet 3/1/3

[RouterA-Ten-GigabitEthernet3/1/3] pim dm

[RouterA-Ten-GigabitEthernet3/1/3] quit

# Enable IP multicast routing and PIM-DM on Router C in the same way Router A is configured. (Details not shown.)

4. Display RPF information for the source on Router B.

[RouterB] display multicast rpf-info 50.1.1.100

RPF information about source 50.1.1.100:

RPF interface: Ten-GigabitEthernet3/1/3, RPF neighbor: 30.1.1.2

Referenced route/mask: 50.1.1.0/24

Referenced route type: igp

Route selection rule: preference-preferred

Load splitting rule: disable

Source AS: 0

C-multicast route target: 0x0000000000000000

The output shows that the current RPF route on Router B is contributed by a unicast routing protocol and the RPF neighbor is Router A.

5. On Router B, configure a static multicast route to the source and specify Router C as the RPF neighbor.

[RouterB] ip rpf-route-static 50.1.1.0 24 20.1.1.2

Verifying the configuration

# Display RPF information for the source on Router B.

[RouterB] display multicast rpf-info 50.1.1.100

RPF information about source 50.1.1.100:

RPF interface: Ten-GigabitEthernet3/1/2, RPF neighbor: 20.1.1.2

Referenced route/mask: 50.1.1.0/24

Referenced route type: multicast static

Route selection rule: preference-preferred

Load splitting rule: disable

Source AS: 0

C-multicast route target: 0x0000000000000000

The output shows the following information:

· The RPF route on Router B is the configured static multicast route.

· The RPF neighbor of Router B is Router C.

Example: Creating an RPF route

Network configuration

As shown in Figure 6:

· PIM-DM runs on the network.

· All routers on the network support IP multicast.

· Router B and Router C run OSPF, and have no unicast routes to Router A.

· Typically, the receiver host receives the multicast data from the source 1 in the OSPF domain.

Configure the routers so that the receiver host can receive multicast data from Source 2, which is outside the OSPF domain.

Figure 6 Network diagram

‌

Procedure

1. Assign an IP address and subnet mask for each interface, as shown in Figure 6. (Details not shown.)

2. Configure OSPF on Router B and Router C. (Details not shown.)

3. Enable IP multicast routing, and enable IGMP and PIM-DM:

# On Router C, enable IP multicast routing.

<RouterC> system-view

[RouterC] multicast routing

[RouterC-mrib] quit

# Enable IGMP on the receiver-side interface Ten-GigabitEthernet 3/1/1.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] igmp enable

[RouterC-Ten-GigabitEthernet3/1/1] quit

# Enable PIM-DM on Ten-GigabitEthernet 3/1/2.

[RouterC] interface ten-gigabitethernet 3/1/2

[RouterC-Ten-GigabitEthernet3/1/2] pim dm

[RouterC-Ten-GigabitEthernet3/1/2] quit

# On Router A, enable IP multicast routing.

<RouterA> system-view

[RouterA] multicast routing

[RouterA-mrib] quit

# Enable PIM-DM on each interface.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] pim dm

[RouterA-Ten-GigabitEthernet3/1/1] quit

[RouterA] interface ten-gigabitethernet 3/1/2

[RouterA-Ten-GigabitEthernet3/1/2] pim dm

[RouterA-Ten-GigabitEthernet3/1/2] quit

# Enable IP multicast routing and PIM-DM on Router B in the same way Router A is configured. (Details not shown.)

4. Display RPF information for Source 2 on Router B and Router C.

[RouterB] display multicast rpf-info 50.1.1.100

[RouterC] display multicast rpf-info 50.1.1.100

No output is displayed because no RPF routes to Source 2 exist on Router B and Router C.

5. Configure a static multicast route:

# Configure a static multicast route on Router B and specify Router A as its RPF neighbor to Source 2.

[RouterB] ip rpf-route-static 50.1.1.0 24 30.1.1.2

# Configure a static multicast route on Router C and specify Router B as its RPF neighbor to Source 2.

[RouterC] ip rpf-route-static 50.1.1.0 24 20.1.1.2

Verifying the configuration

# Display RPF information for Source 2 on Router B.

[RouterB] display multicast rpf-info 50.1.1.100

RPF information about source 50.1.1.100:

RPF interface: Ten-GigabitEthernet3/1/3, RPF neighbor: 30.1.1.2

Referenced route/mask: 50.1.1.0/24

Referenced route type: multicast static

Route selection rule: preference-preferred

Load splitting rule: disable

Source AS: 0

C-multicast route target: 0x0000000000000000

# Display RPF information for Source 2 on Router C.

[RouterC] display multicast rpf-info 50.1.1.100

RPF information about source 50.1.1.100:

RPF interface: Ten-GigabitEthernet3/1/2, RPF neighbor: 20.1.1.2

Referenced route/mask: 50.1.1.0/24

Referenced route type: multicast static

Route selection rule: preference-preferred

Load splitting rule: disable

Source AS: 0

C-multicast route target: 0x0000000000000000

The output shows that the RPF routes to Source 2 exist on Router B and Router C. These RPF routes are the configured static multicast routes .

Example: Configuring multicast forwarding over a GRE tunnel

Network configuration

As shown in Figure 7:

· Multicast routing and PIM-DM are enabled on Router A and Router C. Router B does not support multicast.

· Router A, Router B, and Router C run OSPF. The source-side interface Ten-GigabitEthernet 3/1/1 on Router A does not run OSPF.

Configure a GRE tunnel so that the receiver host can receive the multicast data from the source.

Figure 7 Network diagram

‌

Procedure

1. Assign an IP address and mask for each interface, as shown in Figure 7. (Details not shown.)

2. Configure OSPF on all the routers. Do not enable OSPF on Ten-GigabitEthernet 3/1/1 on Router A. (Details not shown.)

3. Configure a GRE tunnel:

# Create a GRE tunnel interface Tunnel 2 on Router A, and specify the tunnel mode as GRE/IPv4.

<RouterA> system-view

[RouterA] interface tunnel 2 mode gre

# Assign an IP address to interface Tunnel 2, and specify its source and destination addresses.

[RouterA-Tunnel2] ip address 50.1.1.1 24

[RouterA-Tunnel2] source 20.1.1.1

[RouterA-Tunnel2] destination 30.1.1.2

[RouterA-Tunnel2] quit

# Create a GRE tunnel interface Tunnel 2 on Router C, and specify the tunnel mode as GRE/IPv4.

<RouterC> system-view

[RouterC] interface tunnel 2 mode gre

# Assign an IP address to interface Tunnel 2, and specify its source and destination addresses.

[RouterC-Tunnel2] ip address 50.1.1.2 24

[RouterC-Tunnel2] source 30.1.1.2

[RouterC-Tunnel2] destination 20.1.1.1

[RouterC-Tunnel2] quit

4. Enable IP multicast routing, PIM-DM, and IGMP:

# On Router A, enable IP multicast routing.

[RouterA] multicast routing

[RouterA-mrib] quit

# Enable PIM-DM on each interface.

[RouterA] interface ten-gigabitethernet 3/1/1

[RouterA-Ten-GigabitEthernet3/1/1] pim dm

[RouterA-Ten-GigabitEthernet3/1/1] quit

[RouterA] interface ten-gigabitethernet 3/1/2

[RouterA-Ten-GigabitEthernet3/1/2] pim dm

[RouterA-Ten-GigabitEthernet3/1/2] quit

[RouterA] interface tunnel 2

[RouterA-Tunnel2] pim dm

[RouterA-Tunnel2] quit

# On Router C, enable IP multicast routing.

[RouterC] multicast routing

[RouterC-mrib] quit

# Enable IGMP on the receiver-side interface Ten-GigabitEthernet 3/1/1.

[RouterC] interface ten-gigabitethernet 3/1/1

[RouterC-Ten-GigabitEthernet3/1/1] igmp enable

[RouterC-Ten-GigabitEthernet3/1/1] quit

# Enable PIM-DM on other interfaces.

[RouterC] interface ten-gigabitethernet 3/1/2

[RouterC-Ten-GigabitEthernet3/1/2] pim dm

[RouterC-Ten-GigabitEthernet3/1/2] quit

[RouterC] interface tunnel 2

[RouterC-Tunnel2] pim dm

[RouterC-Tunnel2] quit

5. On Router C, configure a static multicast route to the source and specify Router A as the RPF neighbor.

[RouterC] ip rpf-route-static 10.1.1.0 24 50.1.1.1

Verifying the configuration

# Send an IGMP report from Receiver to join multicast group 225.1.1.1. (Details not shown.)

# Send multicast data from the source to multicast group 225.1.1.1. (Details not shown.)

# Display PIM routing entries on Router C.

[RouterC] display pim routing-table

Total 1 (*, G) entry; 1 (S, G) entry

(*, 225.1.1.1)

Protocol: pim-dm, Flag: WC

UpTime: 00:04:25

Upstream interface: NULL

Upstream neighbor: NULL

RPF prime neighbor: NULL

Downstream interface(s) information:

Total number of downstreams: 1

1: Ten-GigabitEthernet3/1/1

Protocol: igmp, UpTime: 00:04:25, Expires: -

(10.1.1.100, 225.1.1.1)

Protocol: pim-dm, Flag: ACT

UpTime: 00:06:14

Upstream interface: Tunnel2

Upstream neighbor: 50.1.1.1

RPF prime neighbor: 50.1.1.1

Downstream interface(s) information:

Total number of downstreams: 1

1: Ten-GigabitEthernet3/1/1

Protocol: pim-dm, UpTime: 00:04:25, Expires: -

The output shows that Router A is the RPF neighbor of Router C and the multicast data from Router A is delivered over the GRE tunnel to Router C.

Troubleshooting multicast routing and forwarding

Static multicast route failure

Symptom

No dynamic routing protocol is enabled on the routers, and the physical status and link layer status of interfaces are both up, but the static multicast route fails.

Solution

To resolve the issue:

1. Use the display multicast routing-table static command to display information about static multicast routes. Verify that the static multicast route has been correctly configured and that the route entry exists in the static multicast routing table.

2. Check the type of interface that connects the static multicast route to the RPF neighbor. If the interface is not a point-to-point interface, be sure to specify the address for the RPF neighbor.

3. If the issue persists, contact H3C Support.

08-IP Multicast Configuration Guide

About multicast routing and forwarding

RPF check implementation in multicast

Changing an RPF route

Creating an RPF route

Multicast forwarding across unicast subnets

Enabling IP multicast routing

About this task

Procedure

Configuring static multicast routes

About this task

Restrictions and guidelines

Procedure

Specifying the longest prefix match principle

Procedure

Configuring multicast load splitting

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Procedure

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Restrictions and guidelines

Procedure

Configuring RPF check failure processing

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Restrictions and guidelines

Procedure

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Restrictions and guidelines

Procedure

Setting the maximum number of cached unknown multicast packets

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Restrictions and guidelines

Procedure

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Proceudre

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Restrictions and guidelines

Proceudre

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Restrictions and guidelines

Proceudre

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Restrictions and guidelines

Proceudre

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Restrictions and guidelines

Proceudre

Enabling SNMP notifications for multicast routing and forwarding

About this task

Procedure

Multicast routing and forwarding configuration examples

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

Network configuration

Procedure

Verifying the configuration

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