Table of Contents

1 Multicast Routing and Forwarding Configuration· 1-1

Multicast Routing and Forwarding Overview· 1-1

Introduction to Multicast Routing and Forwarding· 1-1

RPF Check Mechanism·· 1-1

Multicast Static Routes· 1-4

Multicast Traceroute· 1-5

Configuration Task List 1-6

Configuring Multicast Routing and Forwarding· 1-6

Configuration Prerequisites· 1-6

Enabling IP Multicast Routing· 1-7

Configuring Multicast Static Routes· 1-7

Configuring a Multicast Routing Policy· 1-8

Configuring a Multicast Forwarding Range· 1-9

Configuring the Multicast Forwarding Table Size· 1-9

Tracing a Multicast Path· 1-11

Displaying and Maintaining Multicast Routing and Forwarding· 1-11

Configuration Examples· 1-12

Changing an RPF Route· 1-12

Creating an RPF Route· 1-14

Troubleshooting Multicast Routing and Forwarding· 1-16

Multicast Static Route Failure· 1-16

Multicast Data Fails to Reach Receivers· 1-17

 

When configuring multicast routing and forwarding, go to these sections for information you are interested in:

l          Multicast Routing and Forwarding Overview

l          Configuring Multicast Routing and Forwarding

l          Displaying and Maintaining Multicast Routing and Forwarding

l          Configuration Examples

l          Troubleshooting Multicast Routing and Forwarding

 

 

Multicast Routing and Forwarding Overview

Introduction to Multicast Routing and Forwarding

In multicast implementations, multicast routing and forwarding are implemented by three types of tables:

l          Each multicast routing protocol has its own multicast routing table, such as PIM routing table.

l          The information of different multicast routing protocols forms a general multicast routing table.

l          The multicast forwarding table is directly used to control the forwarding of multicast packets.

A multicast forwarding table consists of a set of (S, G) entries, each indicating the routing information for delivering multicast data from a multicast source to a multicast group. If a router supports multiple multicast protocols, its multicast routing table will include routes generated by multiple protocols. The router chooses the optimal route from the multicast routing table based on the configured multicast routing and forwarding policy and adds the route entry into its multicast forwarding table.

RPF Check Mechanism

A multicast routing protocol relies on the existing unicast routing information, MBGP routes, or multicast static routes in creating multicast routing entries. When creating multicast routing table entries, a multicast routing protocol uses the reverse path forwarding (RPF) check mechanism to ensure multicast data delivery along the correct path. In addition, the RPF check mechanism also helps avoid data loops caused by various reasons.

RPF check process

The basis for an RPF check is a unicast route, an MBGP route, or a multicast static route.

l          A unicast routing table contains the shortest path to each destination subnet,

l          An MBGP routing table contains multicast routing information, and

l          A multicast static routing table contains the RPF routing information defined by the user through static configuration.

When performing an RPF check, a router searches its unicast routing table and multicast static routing table at the same time. The specific process is as follows:

1)        The router first chooses an optimal route from the unicast routing table, MBGP routing table, and multicast static routing table:

l          The router automatically chooses an optimal unicast route by searching its unicast routing table, using the IP address of the “packet source” as the destination address. The outgoing interface in the corresponding routing entry is the RPF interface and the next hop is the RPF neighbor. The router considers the path along which the packet from the RPF neighbor arrived on the RPF interface to be the shortest path that leads back to the source.

l          The router automatically chooses an optimal MBGP route by searching its MBGP routing table, using the IP address of the “packet source” as the destination address. The outgoing interface in the corresponding routing entry is the RPF interface and the next hop is the RPF neighbor.

l          The router automatically chooses an optimal multicast static route by searching its multicast static routing table, using the IP address of the “packet source” as the destination address. The corresponding routing entry explicitly defines the RPF interface and the RPF neighbor.

2)        Then, the router selects one from these three optimal routes as the RPF route. The selection process is as follows:

l          If configured to use the longest match principle, the router selects the longest match route from the three; if these three routes have the same mask, the router selects the route with the highest priority; if the three routes have the same priority, the router selects the RPF route according to the sequence of multicast static route, MBGP route, and unicast route.

l          If not configured to use the longest match principle, the router selects the route with the highest priority; if the three routes have the same priority, the router selects the RPF route according to the sequence of multicast static route, MBGP route, and unicast route.

 

 

Implementation of RPF check in multicast

Implementing an RPF check on each received multicast data packet would bring a big burden to the router. The use of a multicast forwarding table is the solution to this issue. When creating a multicast routing entry and a multicast forwarding entry for a multicast packet, the router sets the RPF interface of the packet as the incoming interface of the (S, G) entry. Upon receiving an (S, G) multicast packet, the router first searches its multicast forwarding table:

1)        If the corresponding (S, G) entry does not exist in the multicast forwarding table, the packet is subject to an RPF check. The router creates a multicast routing entry based on the relevant routing information and adds the entry into the multicast forwarding table, with the RPF interface as the incoming interface.

l          If the interface on which the packet actually arrived is the RPF interface, the RPF check succeeds and the router forwards the packet to all the outgoing interfaces.

l          If the interface on which the packet actually arrived is not the RPF interface, the RPF check fails and the router discards the packet.

2)        If the corresponding (S, G) entry exists, and the interface on which the packet actually arrived is the incoming interface, the router forwards the packet to all the outgoing interfaces.

3)        If the corresponding (S, G) entry exists, but the interface on which the packet actually arrived is not the incoming interface in the multicast forwarding table, the multicast packet is subject to an RPF check.

l          If the RPF interface is the incoming interface of the (S, G) entry, this means the (S, G) entry is correct but the packet arrived from a wrong path. The packet is to be discarded.

l          If the RPF interface is not the incoming interface, this means the (S, G) entry has expired, and router replaces the incoming interface with the RPF interface. If the interface on which the packet arrived in the RPF interface, the router forwards the packet to all the outgoing interfaces; otherwise it discards the packet.

Assume that unicast routes are available in the network, MBGP is not configured, and no multicast static routes have been configured on Router C, as shown in Figure 1-1. Multicast packets travel along the SPT from the multicast source to the receivers. The multicast forwarding table on Router C contains the (S, G) entry, with VLAN-interface 20 as the RPF interface.

Figure 1-1 RPF check process

 

l          When a multicast packet arrives on VLAN-interface 20 of Router C, as the interface is the incoming interface of the (S, G) entry, the router forwards the packet to all outgoing interfaces.

l          When a multicast packet arrives on VLAN-interface 10 of Router C, as the interface is not the incoming interface of the (S, G) entry, the router performs an RPF check on the packet: The router searches its unicast routing table and finds that the outgoing interface to Source (the RPF interface) is VLAN-interface 20. This means the (S, G) entry is correct and packet arrived along a wrong path. The RPF check fails and the packet is discarded.

Multicast Static Routes

A multicast static route is an important basis for RPF check. Depending on the application environment, a multicast static route has the following two functions:

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. By configuring a multicast static route for a given multicast source, you can change the RPF route so as to create a transmission path for multicast traffic different from that for unicast traffic.

Figure 1-2 Changing an RPF route

 

As shown in Figure 1-2, when no multicast static route is configured, Router C’s RPF neighbor on the path back to Source is Router A and the multicast information from Source travels along the path from Router A to Router C, which is the unicast route between the two routers; with a static route configured on Router C and with Router B as Router C’s RPF neighbor on the path back to Source, the multicast information from Source travels from Router A to Router B and then to Router C.

Creating an RPF route

When a unicast route is blocked, multicast traffic forwarding is stopped due to lack of an RPF route. By configuring a multicast static route for a given multicast source, you can create an RPF route so that a multicast routing entry is created to guide multicast traffic forwarding.

Figure 1-3 Creating an RPF route

 

As shown in Figure 1-3, the RIP domain and the OSPF domain are unicast isolated from each other. When no multicast static route is configured, the hosts (Receivers) in the OSPF domain cannot receive the multicast packets sent by the multicast source (Source) in the RIP domain. After you configure a multicast static route on Router C and Router D, specifying Router B as the RPF neighbor of Router C and specifying Router C as the RPF neighbor of Router D, the receivers can receive multicast data sent by the multicast source.

 

 

Multicast Traceroute

The multicast traceroute utility is used to trace the path that a multicast stream flows down from the first-hop router to the last-hop router.

Concepts in multicast traceroute

1)        Last-hop router: If a router has one of its interfaces connecting to the subnet the given destination address is on, and if the router is able to forward multicast streams from the given multicast source onto that subnet, that router is called last-hop router.

2)        First-hop router: the router that directly connects to the multicast source.

3)        Querier: the router requesting the multicast traceroute.

Introduction to multicast traceroute packets

A multicast traceroute packet is a special IGMP packet, which differs from common IGMP packets in that its IGMP Type field is set to 0x1F or 0x1E and that its destination IP address is a unicast address. There are three types of multicast traceroute packets:

l          Query, with the IGMP Type field set to 0x1F,

l          Request, with the IGMP Type field set to 0x1F, and

l          Response, with the IGMP Type field set to 0x1E.

Process of multicast traceroute

1)        The querier sends a query to the last-hop router.

2)        Upon receiving the query, the last-hop router turns the query packet into a request packet by adding a response data block containing its interface addresses and packet statistics to the end of the packet, and forwards the request packet via unicast to the previous hop for the given multicast source and group.

3)        From the last-hop router to the multicast source, each hop adds a response data block to the end of the request packet and unicasts it to the previous hop.

4)        When the first-hop router receives the request packet, it changes the packet type to indicate a response packet, and then sends the completed packet via unicast to the multicast traceroute querier.

Configuration Task List

Complete these tasks to configure multicast routing and forwarding:

Task	Remarks
Enabling IP Multicast Routing	Required
Configuring Multicast Static Routes	Optional
Configuring a Multicast Routing Policy	Optional
Configuring a Multicast Forwarding Range	Optional
Configuring the Multicast Forwarding Table Size	Optional
Tracing a Multicast Path	Optional

 

Configuring Multicast Routing and Forwarding

Configuration Prerequisites

Before configuring multicast routing and forwarding, complete the following tasks:

l          Configure a unicast routing protocol so that all devices in the domain are interoperable at the network layer.

l          Enable PIM (PIM-DM or PIM-SM).

Before configuring multicast routing and forwarding, prepare the following data:

l          The maximum number of downstream nodes for a single multicast forwarding table entry

l          The maximum number of entries in the multicast forwarding table

Enabling IP Multicast Routing

Before configuring any Layer 3 multicast functionality, you must enable IP multicast routing.

Enabling IP multicast routing in the public instance

Follow these steps to enable IP multicast routing in the public instance:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable IP multicast routing	multicast routing-enable	Required Disabled by default

 

Enabling IP multicast routing in a VPN instance

Follow these steps to enable IP multicast routing in a VPN instance:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Create a VPN instance and enter VPN instance view	ip vpn-instance vpn-instance-name	—
Configure a route distinguisher (RD) for the VPN instance	route-distinguisher route-distinguisher	Required No RD is configured by default.
Enable IP multicast routing	multicast routing-enable	Required Disabled by default

 

IP multicast does not support the use of secondary IP address segments. Namely, multicast can be routed and forwarded only through primary IP addresses, rather than secondary addresses, even if configured on interfaces.

 

 

Configuring Multicast Static Routes

By configuring a multicast static route for a given multicast source, you can specify an RPF interface or an RPF neighbor for multicast traffic from that source.

Follow these steps to configure a multicast static route:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Configure a multicast static route	ip rpf-route-static [ vpn-instance vpn-instance-name ] source-address { mask | mask-length } [ protocol [ process-id ] ] [ route-policy policy-name ] { rpf-nbr-address | interface-type interface-number } [ preference preference ] [ order order-number ]	Required No multicast static route configured by default.

 

 

Configuring a Multicast Routing Policy

You can configure the router to determine the RPF route based on the longest match principle. For details about RPF route selection, refer to RPF check process.

By configuring per-source or per-source-and-group load splitting, you can optimize the traffic delivery when multiple data flows are handled.

Configuring a multicast routing policy in the public instance

Follow these steps to configure a multicast routing policy in the public instance:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Configure the device to select the RPF route based on the longest match	multicast longest-match	Required The route with the highest priority is selected as the RPF route by default
Configure multicast load splitting	multicast load-splitting { source | source-group }	Optional Disabled by default

 

Configuring a multicast routing policy in a VPN instance

Follow these steps to configure a multicast routing policy in a VPN instance:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VPN instance view	ip vpn-instance vpn-instance-name	—
Configure the device to select the RPF route based on the longest match	multicast longest-match	Required The route with the highest priority is selected as the RPF route by default
Configure multicast load splitting	multicast load-splitting { source | source-group }	Optional Disabled by default

 

Configuring a Multicast Forwarding Range

Multicast packets do not travel without a boundary in a network. The multicast data corresponding to each multicast group must be transmitted within a definite scope. Presently, you can define a multicast forwarding range by:

l          Specifying boundary interfaces, which form a closed multicast forwarding area, or

l          Setting the minimum time to live (TTL) value required for a multicast packet to be forwarded.

You can configure a forwarding boundary specific to a particular multicast group on all interfaces that support multicast forwarding. A multicast forwarding boundary sets the boundary condition for the multicast groups in the specified range. If the destination address of a multicast packet matches the set boundary condition, the packet will not be forwarded. Once a multicast boundary is configured on an interface, this interface can no longer forward multicast packets (including packets sent from the local device) or receive multicast packets.

You can configure the minimum TTL required for a multicast packet to be forwarded on all interfaces that support multicast forwarding. Before being forwarded from an interface, every multicast packet (including multicast packet from the local device) is subject to a TTL check:

l          If the TTL value of the packet (already decremented by 1 on this router) is larger than the minimum TTL value configured on the interface, the packet will be forwarded.

l          If the TTL value of the packet is smaller than or equal to the minimum TTL value configured on the interface, the packet will be discarded.

The configuration of the minimum TTL value required for a multicast packet is not supported on the S7500E Series Ethernet Switches.

Follow these steps to configure a multicast forwarding range:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configure a multicast forwarding boundary	multicast boundary group-address { mask | mask-length }	Required No forwarding boundary by default

 

Configuring the Multicast Forwarding Table Size

The router maintains the corresponding forwarding entry for each multicast packet it receives. Excessive multicast routing entries, however, can exhaust the router’s memory and thus result in lower router performance. You can set a limit on the number of entries in the multicast forwarding table based on the actual networking situation and the performance requirements. If the configured maximum number of multicast forwarding table entries is smaller than the current value, the forwarding entries in excess will not be immediately deleted; instead they will be deleted by the multicast routing protocol running on the router. The router will no longer add new multicast forwarding entries until the number of existing multicast forwarding entries comes down below the configured value.

When forwarding multicast traffic, the router replicates a copy of the multicast traffic for each downstream node and forwards the traffic, and thus each of these downstream nodes forms a branch of the multicast distribution tree. You can configure the maximum number of downstream nodes (namely, the maximum number of outgoing interfaces) for a single entry in the multicast forwarding table to lessen burden on the router for replicating multicast traffic. If the configured maximum number of downstream nodes for a single multicast forwarding entry is smaller than the current number, the downstream nodes in excess will not be deleted immediately; instead they must be deleted by the multicast routing protocol. The router will no longer add new multicast forwarding entries for newly added downstream nodes until the number of existing downstream nodes comes down below the configured value.

Configuring the multicast forwarding table size in the public instance

Follow these steps to configure the multicast forwarding table size in the public instance:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Configure the maximum number of entries in the multicast forwarding table	multicast forwarding-table route-limit limit	Optional The default is the maximum number allowed by the system, namely 1000.
Configure the maximum number of downstream nodes for a single multicast forwarding entry	multicast forwarding-table downstream-limit limit	Optional The default is the maximum number allowed by the system, namely 128.

 

Configuring the multicast forwarding table size in a VPN instance

Follow these steps to configure the multicast forwarding table size in a VPN instance:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VPN instance view	ip vpn-instance vpn-instance-name	—
Configure the maximum number of entries in the multicast forwarding table	multicast forwarding-table route-limit limit	Optional The default is the maximum number allowed by the system, namely 1000.
Configure the maximum number of downstream nodes for a single route in the multicast forwarding table	multicast forwarding-table downstream-limit limit	Optional The default is the maximum number allowed by the system, namely 128.

 

Tracing a Multicast Path

You can run the mtracert command to trace the path down which the multicast traffic flows from a given first-hop router to the last-hop router.

To do…	Use the command…	Remarks
Trace a multicast path	mtracert source-address [ [ last-hop-router-address ] group-address ]	Required Available in any view

 

Displaying and Maintaining Multicast Routing and Forwarding

To do...	Use the command...	Remarks
View the multicast boundary information	display multicast [ all-instance | vpn-instance vpn-instance-name ] boundary [ group-address [ mask | mask-length ] ] [ interface interface-type interface-number ]	Available in any view
View the multicast forwarding table information	display multicast [ all-instance | vpn-instance vpn-instance-name ] forwarding-table [ source-address [ mask { mask | mask-length } ] | group-address [ mask { mask | mask-length } ] | incoming-interface { interface-type interface-number | register } | outgoing-interface { { exclude | include | match } { interface-type interface-number | register } } | statistics | slot slot-number ] * [ port-info ]	Available in any view
View the multicast routing table information	display multicast [ all-instance | vpn-instance vpn-instance-name ] routing-table [ source-address [ mask { mask | mask-length } ] | group-address [ mask { mask | mask-length } ] | incoming-interface { interface-type interface-number | register } | outgoing-interface { { exclude | include | match } { interface-type interface-number | register } } ] *	Available in any view
View the information of the multicast static routing table	display multicast routing-table [ all-instance | vpn-instance vpn-instance-name ] static [ config ] [ source-address { mask-length | mask } ]	Available in any view
View the RPF route information of the specified multicast source	display multicast [ all-instance | vpn-instance vpn-instance-name ] rpf-info source-address [ group-address ]	Available in any view
Clear forwarding entries from the multicast forwarding table	reset multicast [ all-instance | vpn-instance vpn-instance-name ] forwarding-table { { source-address [ mask { mask | mask-length } ] | group-address [ mask { mask | mask-length } ] | incoming-interface { interface-type interface-number | register } } * | all }	Available in user view
Clear routing entries from the multicast routing table	reset multicast [ all-instance | vpn-instance vpn-instance-name ] routing-table { { source-address [ mask { mask | mask-length } ] | group-address [ mask { mask | mask-length } ] | incoming-interface { interface-type interface-number | register } } * | all }	Available in user view

 

 

Configuration Examples

Changing an RPF Route

Network requirements

l          PIM-DM runs in the network. All switches in the network support multicast.

l          Switch A, Switch B and Switch C run OSPF.

l          Typically, Receiver can receive the multicast data from Source through the path Switch A – Switch B, which is the same as the unicast route.

l          Perform the following configuration so that Receiver can receive the multicast data from Source through the path Switch A – Switch C – Switch B, which is different from the unicast route.

Network diagram

Figure 1-4 Network diagram for RPF route alternation configuration

 

Configuration procedure

1)        Configure IP addresses and unicast routing

Configure the IP address and subnet mask for each interface as per Figure 1-4. The detailed configuration steps are omitted here.

Enable OSPF on the switches in the PIM-DM domain. Ensure the network-layer interoperation among the switches in the PIM-DM domain. Ensure that the switches can dynamically update their routing information by leveraging the unicast routing protocol. The specific configuration steps are omitted here.

2)        Enable IP multicast routing, and enable PIM-DM and IGMP

# Enable IP multicast routing on Switch B, enable PIM-DM on each interface, and enable IGMP on the host-side interface VLAN-interface 100.

<SwitchB> system-view

[SwitchB] multicast routing-enable

[SwitchB] interface vlan-interface 100

[SwitchB-Vlan-interface100] igmp enable

[SwitchB-Vlan-interface100] pim dm

[SwitchB-Vlan-interface100] quit

[SwitchB] interface vlan-interface 101

[SwitchB-Vlan-interface101] pim dm

[SwitchB-Vlan-interface101] quit

[SwitchB] interface vlan-interface 102

[SwitchB-Vlan-interface102] pim dm

[SwitchB-Vlan-interface102] quit

# Enable IP multicast routing on Switch A, and enable PIM-DM on each interface.

<SwitchA> system-view

[SwitchA] multicast routing-enable

[SwitchA] interface vlan-interface 200

[SwitchA-Vlan-interface200] pim dm

[SwitchA-Vlan-interface200] quit

[SwitchA] interface vlan-interface 102

[SwitchA-Vlan-interface102] pim dm

[SwitchA-Vlan-interface102] quit

[SwitchA] interface vlan-interface 103

[SwitchA-Vlan-interface103] pim dm

[SwitchA-Vlan-interface103] quit

The configuration on Switch C is similar to the configuration on Switch A. The specific configuration steps are omitted here.

# Use the display multicast rpf-info command to view the RPF route to Source on Switch B.

[SwitchB] display multicast rpf-info 50.1.1.100

 RPF information about source 50.1.1.100:

     RPF interface: Vlan-interface102, 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

As shown above, the current RPF route on Switch B is contributed by a unicast routing protocol and the RPF neighbor is Switch A.

3)        Configure a multicast static route

# Configure a multicast static route on Switch B, specifying Switch C as its RPF neighbor on the route to Source.

[SwitchB] ip rpf-route-static 50.1.1.100 24 20.1.1.2

4)        Verify the configuration

# Use the display multicast rpf-info command to view the information about the RPF route to Source on Switch B.

[SwitchB] display multicast rpf-info 50.1.1.100

 RPF information about source 50.1.1.100:

     RPF interface: Vlan-interface101, 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

As shown above, the RPF route on Switch B has changed. It is now the configured multicast static route, and the RPF neighbor is now Switch C.

Creating an RPF Route

Network requirements

l          PIM-DM runs in the network and all switches in the network support IP multicast.

l          Switch B and Switch C run OSPF, and have no unicast routes to Switch A.

l          Typically, Receiver can receive the multicast data from Source 1 in the OSPF domain.

l          Perform the following configuration so that Receiver can receive multicast data from Source 2, which is outside the OSPF domain.

Network diagram

Figure 1-5 Network diagram for creating an RPF route

 

Configuration procedure

1)        Configure IP addresses and unicast routing

Configure the IP address and subnet mask for each interface as per Figure 1-5. The detailed configuration steps are omitted here.

Enable OSPF on Switch B and Switch C. Ensure the network-layer interoperation among Switch B and Switch C. Ensure that the switches can dynamically update their routing information by leveraging the unicast routing protocol. The specific configuration steps are omitted here.

2)        Enable IP multicast routing, and enable PIM-DM and IGMP

# Enable IP multicast routing on Switch C, enable PIM-DM on each interface, and enable IGMP on the host-side interface VLAN-interface 100.

<SwitchC> system-view

[SwitchC] multicast routing-enable

[SwitchC] interface vlan-interface 100

[SwitchC-Vlan-interface100] igmp enable

[SwitchC-Vlan-interface100] pim dm

[SwitchC-Vlan-interface100] quit

[SwitchC] interface vlan-interface 101

[SwitchC-Vlan-interface101] pim dm

[SwitchC-Vlan-interface101] quit

# Enable IP multicast routing on Switch A and enable PIM-DM on each interface.

<SwitchA> system-view

[SwitchA] multicast routing-enable

[SwitchC] interface vlan-interface 300

[SwitchC-Vlan-interface300] pim dm

[SwitchC-Vlan-interface300] quit

[SwitchC] interface vlan-interface 102

[SwitchC-Vlan-interface102] pim dm

[SwitchC-Vlan-interface102] quit

The configuration on Switch B is similar to that on Switch A. The specific configuration steps are omitted here.

# Use the display multicast rpf-info command to view the RPF routes to Source 2 on Switch B and Switch C.

[SwitchB] display multicast rpf-info 50.1.1.100

[SwitchC] display multicast rpf-info 50.1.1.100

No information is displayed. This means that no RPF route to Source 2 exists on Switch B and Switch C.

3)        Configure a multicast static route

# Configure a multicast static route on Switch B, specifying Switch A as its RPF neighbor on the route to Source 2.

[SwitchB] ip rpf-route-static 50.1.1.100 24 30.1.1.2

# Configure a multicast static route on Switch C, specifying Switch B as its RPF neighbor on the route to Source 2.

[SwitchC] ip rpf-route-static 50.1.1.100 24 20.1.1.2

4)        Verify the configuration

# Use the display multicast rpf-info command to view the RPF routes to Source 2 on Switch B and Switch C.

[SwitchB] display multicast rpf-info 50.1.1.100

 RPF information about source 50.1.1.100:

     RPF interface: Vlan-interface102, 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

[SwitchC] display multicast rpf-info 50.1.1.100

 RPF information about source 50.1.1.100:

     RPF interface: Vlan-interface101, 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

As shown above, the RPF routes to Source 2 exist on Switch B and Switch C. The source is the configured static route.

Troubleshooting Multicast Routing and Forwarding

Multicast Static Route Failure

Symptom

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

Analysis

l          If the multicast static route is not configured or updated correctly to match the current network conditions, the route entry and the configuration information of multicast static routes do not exist in the multicast routing table.

l          If the optimal route is found, the multicast static route may also fail.

Solution

1)        In the configuration, you can use the display multicast routing-table static config command to view the detailed configuration information of multicast static routes to verify that the multicast static route has been correctly configured and the route entry exists.

2)        In the configuration, you can use the display multicast routing-table static command to view the information of multicast static routes to verify that the multicast static route has been correctly configured and the route entry exists in the multicast routing table.

3)        Check the next hop interface type of the multicast static route. If the interface is not a point-to-point interface, be sure to specify the next hop address to configure the outgoing interface when you configure the multicast static route.

4)        Check that the multicast static route matches the specified routing protocol. If a protocol was specified in multicast static route configuration, enter the display ip routing-table command to check if an identical route was added by the protocol.

5)        Check that the multicast static route matches the specified routing policy. If a routing policy was specified when the multicast static route was configured, enter the display route-policy command to check the configured routing policy.

Multicast Data Fails to Reach Receivers

Symptom

The multicast data can reach some routers but fails to reach the last hop router.

Analysis

If a multicast forwarding boundary has been configured through the multicast boundary command, any multicast packet will be kept from crossing the boundary.

Solution

1)        Use the display pim routing-table command to check whether the corresponding (S, G) entries exist on the router. If so, the router has received the multicast data; otherwise, the router has not received the data.

2)        Use the display multicast boundary command to view the multicast boundary information on the interfaces. Use the multicast boundary command to change the multicast forwarding boundary setting.

3)        In the case of PIM-SM, use the display current-configuration command to check the BSR and RP information.