Contents

Configuring IPv6 multicast routing and forwarding· 1

About IPv6 multicast routing and forwarding· 1

RPF check mechanism·· 1

IPv6 mtrace· 3

IPv6 multicast routing and forwarding tasks at a glance· 3

Prerequisites for IPv6 multicast routing and forwarding· 4

Enabling IPv6 multicast routing· 4

Specifying the longest prefix match principle· 4

Configuring IPv6 multicast load splitting· 4

Configuring an IPv6 multicast forwarding boundary· 5

Configuring RPF check failure processing· 5

Configuring the device to flood RPF-check-failed IPv6 multicast data packets in all VLANs· 5

Configuring the device to multicast RPF-check-failed IPv6 multicast data packets in a VLAN·· 6

Configuring the device to send RPF-check-failed IPv6 multicast data packets to the CPU·· 7

Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN·· 7

Using mtrace2 to trace an IPv6 multicast path·· 8

Display and maintenance commands for IPv6 multicast routing and forwarding· 8

 

Configuring IPv6 multicast routing and forwarding

About IPv6 multicast routing and forwarding

Each IPv6 multicast routing protocol has its own routing table. Multicast routing information in routing entries generated by the IPv6 multicast routing protocols are summarized in a set of (S, G) and (*, G) entries. All the (S, G) and (*, G) entries form a general IPv6 multicast routing table. The optimal IPv6 multicast routing entries in the general IPv6 multicast routing table are added to the IPv6 multicast forwarding table to guide IPv6 multicast data forwarding.

RPF check mechanism

An IPv6 multicast routing protocol uses the reverse path forwarding (RPF) check mechanism to ensure IPv6 multicast data delivery along the correct path and to avoid data loops.

RPF check process

An IPv6 multicast device performs the RPF check on an IPv6 multicast packet as follows:

1.        Chooses an optimal route back to the packet source separately from the IPv6 unicast and IPv6 MBGP routing tables.

In RPF check, the "packet source" means difference things in difference situations:

¡  For a packet that travels along the SPT, the packet source is the IPv6 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 IPv6 PIM."

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

¡  If the device uses the longest prefix match principle, the route with a higher prefix length becomes the RPF route. If the routes have the same prefix length, the route with a higher route preference becomes the RPF route. If the routes have the same route preference, the IPv6 MBGP route becomes the RPF route. If equal cost routes exist, the equal cost route with the highest next hop IPv6 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 a higher route preference becomes the RPF route. If the routes have the same route preference, the IPv6 MBGP route becomes the RPF route. If equal cost routes exist, the equal cost route with the highest next hop IPv6 address becomes the RPF route.

In the RPF route, the outgoing interface is the RPF interface and the next hop is the RPF neighbor.

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 IPv6 multicast

Implementing an RPF check on each received IPv6 multicast packet would heavily burden the device. The use of an IPv6 multicast forwarding table is the solution to this issue. When the device creates an IPv6 multicast forwarding entry for an IPv6 (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 its IPv6 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. Then, it creates a forwarding entry with the RPF interface as the incoming interface and performs one of the following tasks:

¡  If the receiving interface is the RPF interface, the RPF check succeeds and the device forwards the packet out of all 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 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 tasks:

¡  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 IPv6 unicast routes are available on the network. IPv6 MBGP is not configured. IPv6 multicast packets travel along the SPT from the multicast source to the receivers. The IPv6 multicast forwarding table on Device C contains the (S, G) entry, with Port A as the RPF interface.

·          If an IPv6 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 an IPv6 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 IPv6 unicast routing table and finds that the outgoing interface to the source (the RPF interface) is Port A. This means that 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.

IPv6 mtrace

IPv6 mtrace uses mtrace2 to trace the path along which IPv6 multicast group data travels from a source to a destination.

Device roles

IPv6 mtrace includes the following roles:

·          Last-hop router (LHR)—An LHR is a router that has an IPv6 multicast-enabled interface on the same subnet as the destination and can forward specific IPv6 multicast data to the subnet.

·          First-hop router (FHR)—An FHR is a router that is directly connected to the IPv6 multicast source.

·          Client—A client is a router that initiates an mtrace2.

Process

The IPv6 mtrace process is as follows:

1.        The client sends an mtrace2 Query message (with a hops field indicating the maximum number of hops to be traced) to the destination.

2.        The LHR turns the received Query message to an mtrace2 Request message by adding local forwarding information and sends the Request message to the upstream neighbor.

3.        Each router along the traced path adds its local forwarding information to the received Request message and sends the Request message to its upstream neighbor.

4.        The FHR adds its local forwarding information to the received Request message. Then, it turns the Request message to an mtrace2 Reply message and sends the Reply message to the client.

5.        The client interprets forwarding information in the Reply message and displays the information.

IPv6 multicast routing and forwarding tasks at a glance

To configure IPv6 multicast routing and forwarding, perform the following tasks:

1.        Enabling IPv6 multicast routing

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

3.        (Optional.) Configuring IPv6 multicast load splitting

4.        (Optional.) Configuring an IPv6 multicast forwarding boundary

5.        (Optional.) Configuring RPF check failure processing

¡  Configuring the device to flood RPF-check-failed IPv6 multicast data packets in all VLANs

¡  Configuring the device to multicast RPF-check-failed IPv6 multicast data packets in a VLAN

¡  Configuring the device to send RPF-check-failed IPv6 multicast data packets to the CPU

6.        (Optional.) Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN

7.        (Optional.) Using mtrace2 to trace an IPv6 multicast path

Prerequisites for IPv6 multicast routing and forwarding

Before you configure multicast routing and forwarding, configure an IPv6 unicast routing protocol so that all devices in the domain can interoperate at the network layer.

Enabling IPv6 multicast routing

About IPv6 multicast routing

Enable IPv6 multicast routing before you configure any Layer 3 IPv6 multicast functionality.

Procedure

1.        Enter system view.

system-view

2.        Enable IPv6 multicast routing and enter IPv6 MRIB view.

ipv6 multicast routing

By default, IPv6 multicast routing is disabled.

Specifying the longest prefix match principle

About the longest prefix match principle

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 IPv6 MRIB view.

ipv6 multicast routing

3.        Specify the longest prefix match principle for RPF route selection.

longest-match

By default, the route preference principle is used.

Configuring IPv6 multicast load splitting

About IPv6 multicast load splitting

You can enable the device to split multiple IPv6 multicast data flows on a per-source basis or on a per-source-and-group basis.

Procedure

1.        Enter system view.

system-view

2.        Enter IPv6 MRIB view.

ipv6 multicast routing

3.        Configure IPv6 multicast load splitting.

load-splitting { source | source-group }

By default, IPv6 multicast load splitting is disabled.

Configuring an IPv6 multicast forwarding boundary

About IPv6 multicast forwarding boundaries

You can configure an interface as an IPv6 multicast forwarding boundary for an IPv6 multicast group range. The interface cannot receive or forward IPv6 multicast packets for the groups in the range.

Restrictions and guidelines

You do not need to enable IPv6 multicast routing before this configuration.

Procedure

1.        Enter system view.

system-view

2.        Enter interface view.

interface interface-type interface-number

3.        Configure an IPv6 multicast forwarding boundary.

ipv6 multicast boundary { ipv6-group-address prefix-length | scope { scope-id | admin-local | global | organization-local | site-local } }

By default, an interface is not an IPv6 multicast forwarding boundary for any IPv6 multicast groups.

Configuring RPF check failure processing

Configuring the device to flood RPF-check-failed IPv6 multicast data packets in all VLANs

About flooding RPF-check-failed IPv6 multicast data packets in all VLANs

In some networks, multicast receivers might exist in VLANs to which RPF-check-failed IPv6 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 IPv6 multicast routing before this configuration.

Procedure

1.        Enter system view.

system-view

2.        Configure the device to flood RPF-check-failed IPv6 multicast data packets in all VLANs.

ipv6 multicast rpf-fail-pkt flooding

By default, RPF-check-failed IPv6 multicast data packets are not flooded in all VLANs.

3.        Return to user view.

quit

4.        Clear all IPv6 multicast forwarding entries.

reset ipv6 multicast forwarding-table all

The ipv6 multicast rpf-fail-pkt flooding command takes effect only after you perform this step.

Configuring the device to multicast RPF-check-failed IPv6 multicast data packets in a VLAN

About multicasting RPF-check-failed IPv6 multicast data packets in a VLAN

In some networks, multicast receivers might exist in the VLAN to which RPF-check-failed IPv6 multicast data packets belong. For the receivers to receive the packets, you can configure the device to flood the packets in the VLAN.

Restrictions and guidelines

When you configure the device to multicast RPF-check-failed IPv6 multicast data packets in a VLAN, follow these restrictions and guidelines:

·          Make sure MLD snooping is enabled in the VLAN.

·          Make sure a Layer 3 IPv6 multicast routing protocol (such as MLD or IPv6 PIM) runs on the VLAN interface.

·          RPF-check-failed IPv6 multicast data packets can be multicast in a VLAN only when associated MLD snooping forwarding entries exist in the VLAN.

You do not need to enable IPv6 multicast routing before this configuration.

Procedure

1.        Enter system view.

system-view

2.        Configure the device to flood RPF-check-failed IPv6 multicast data packets in all VLANs.

ipv6 multicast rpf-fail-pkt flooding

By default, RPF-check-failed IPv6 multicast data packets are not flooded in all VLANs.

3.        Enter VLAN interface view.

interface vlan-interface vlan-interface-id

4.        Configure the device to multicast RPF-check-failed multicast data packets in the VLAN.

ipv6 multicast rpf-fail-pkt bridging

By default, multicast RPF-check-failed multicast data packets are not multicast in a VLAN.

5.        Return to system view.

quit

6.        Return to user view.

quit

7.        Clear dynamic MLD snooping group entries.

reset mld-snooping group all [ vlan vlan-id ]

The ipv6 multicast rpf-fail-pkt bridging command takes effect only after you perform this step.

For more information about this command, see IP Multicast Command Reference.

Configuring the device to send RPF-check-failed IPv6 multicast data packets to the CPU

About sending RPF-check-failed IPv6 multicast data packets to the CPU

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

·          If an IPv6 multicast data packet arrives on an outgoing interface of the corresponding IPv6 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 IPv6 PIM."

·          Assume that the SPT and RPT have different incoming interfaces on the receiver-side DR in an IPv6 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 IPv6 multicast packets that travel along the SPT will fail the RPF check and be discarded. If the RPT is pruned at this moment, the IPv6 multicast service is instantaneously interrupted.

To avoid this problem, you can configure the device to deliver 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 IPv6 multicast routing before this configuration.

Procedure

1.        Enter system view.

system-view

2.        Configure the device to send RPF-check-failed IPv6 multicast data packets to the CPU.

ipv6 multicast rpf-fail-pkt trap-to-cpu

By default, RPF-check-failed IPv6 multicast data packets are not sent to the CPU.

3.        Return to user view.

quit

4.        Clear all IPv6 multicast forwarding entries.

reset ipv6 multicast forwarding-table all

The ipv6 multicast rpf-fail-pkt trap-to-cpu command takes effect only after you perform this step.

Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN

About IPv6 multicast forwarding between sub-VLANs of a super VLAN

A super VLAN is associated with multiple sub-VLANs. Sub-VLANs are isolated with each other at Layer 2. For information about super VLANs and sub-VLANs, see Layer 2—LAN Switching Configuration Guide.

Procedure

1.        Enter system view.

system-view

2.        Enter VLAN interface view.

interface vlan-interface interface-number

3.        Enable IPv6 multicast forwarding between sub-VLANs that are associated with a super VLAN.

ipv6 multicast forwarding supervlan community

By default, IPv6 multicast data cannot be forwarded among sub-VLANs that are associated with a super VLAN.

4.        Return to system view.

quit

5.        Return to user view.

quit

6.        Clear all IPv6 multicast forwarding entries with super VLAN interface as the incoming interface.

reset ipv6 multicast forwarding-table incoming-interface { interface-type interface-number }

The ipv6 multicast forwarding supervlan community command takes effect only after you perform this step.

Using mtrace2 to trace an IPv6 multicast path

Restrictions and guidelines

For successful IPv6 mtrace, do not use a UDP port number used by other modules.

You must specify the same UDP port number on all devices on the traced path.

Procedure

1.        Enter system view.

system-view

2.        (Optional.) Specify the UDP port number used by IPv6 mtrace.

ipv6 mtrace-service port number

By default, IPv6 mtrace uses UDP port number 10240.

3.        Use mtrace2 to trace an IPv6 multicast path.

mtrace v2 ipv6 { source-address | group-address } * [ destination address | port number | wait-time time | max-hop count ] * [ verbose ]

The UDP port number specified in this command must be the same as that specified in the mtrace-service port command.

Display and maintenance commands for IPv6 multicast routing and forwarding

	CAUTION: The reset commands might cause IPv6 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 IPv6 MRIB.	display ipv6 mrib interface [ interface-type interface-number ]
Display IPv6 multicast boundary information.	display ipv6 multicast boundary { group [ ipv6-group-address [ prefix-length ] ] | scope [ scope-id ] } [ interface interface-type interface-number ]
Display IPv6 multicast fast forwarding entries.	display ipv6 multicast fast-forwarding cache [ ipv6-source-address | ipv6-group-address ] * [ slot slot-number ]
Display statistics for IPv6 multicast forwarding events.	display ipv6 multicast forwarding event [ slot slot-number ]
Display IPv6 multicast forwarding entries.	display ipv6 multicast forwarding-table [ ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface interface-type interface-number | outgoing-interface { exclude | include | match } interface-type interface-number | slot slot-number | statistics ] *
Display IPv6 multicast routing entries.	display ipv6 multicast routing-table [ ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface interface-type interface-number | outgoing-interface { exclude | include | match } interface-type interface-number ] *
Display RPF information for an IPv6 multicast source.	display ipv6 multicast rpf-info ipv6-source-address [ ipv6-group-address ]
Clear IPv6 multicast fast forwarding entries.	reset ipv6 multicast fast-forwarding cache { { ipv6-source-address | ipv6-group-address } * | all } [ slot slot-number ]
Clear statistics for IPv6 multicast forwarding events.	reset ipv6 multicast forwarding event
Clear IPv6 multicast forwarding entries.	reset ipv6 multicast forwarding-table { { ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface { interface-type interface-number } } * | all }
Clear IPv6 multicast routing entries.	reset ipv6 multicast routing-table { { ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface interface-type interface-number } * | all }

 

	NOTE: ·      When you clear an IPv6 multicast routing entry, the associated IPv6 multicast forwarding entry is also cleared. ·      When you clear an IPv6 multicast forwarding entry, the associated IPv6 multicast routing entry is also cleared.