Contents

Configuring IPv6 multicast routing and forwarding· 1

Overview·· 1

RPF check mechanism·· 1

IPv6 multicast routing and forwarding configuration task list 3

Enabling IPv6 multicast routing· 3

Configuring IPv6 multicast routing and forwarding· 3

Specifying the longest prefix match principle· 3

Configuring IPv6 multicast load splitting· 4

Configuring an IPv6 multicast forwarding boundary· 4

Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN·· 4

Displaying and maintaining IPv6 multicast routing and forwarding· 5

 

Configuring IPv6 multicast routing and forwarding

Overview

IPv6 multicast routing and forwarding uses the following tables:

·          IPv6 multicast protocols' routing tables, such as the IPv6 PIM routing table.

·          General IPv6 multicast routing table that summarizes the multicast routing information generated by different IPv6 multicast routing protocols. The IPv6 multicast routing information from IPv6 multicast sources to IPv6 multicast groups are stored in a set of (S, G) routing entries.

·          IPv6 multicast forwarding table that guides IPv6 multicast forwarding. The optimal routing entries in the IPv6 multicast routing table are added to the IPv6 multicast forwarding table.

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

1.        The router 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.        The router selects one of the optimal routes as the RPF route as follows:

¡  If the router 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.

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

¡  If the router 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.

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

3.        The router checks whether the packet arrived at the RPF interface. If yes, the RPF check succeeds and the packet is forwarded. If not, 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 router. The use of an IPv6 multicast forwarding table is the solution to this issue. When the router 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 router 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 router 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 router forwards the packet out of all outgoing interfaces.

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

·          If a match is found and the matching forwarding entry contains the receiving interface, the router 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 router determines the RPF route back to the packet source. Then, the router 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 router discards the packet.

¡  If the RPF interface is not the incoming interface, it means that the forwarding entry has expired. The router 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 router forwards the packet out of all outgoing interfaces. Otherwise, it discards the packet.

Figure 1 RPF check process

‌

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 VLAN-interface 20 as the RPF interface.

·          If an IPv6 multicast packet arrives at Device C on VLAN-interface 20, 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 VLAN-interface 10, 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 VLAN-interface 20. 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 multicast routing and forwarding configuration task list

Tasks at a glance
(Required.) Enabling IPv6 multicast routing
(Optional.) Configuring IPv6 multicast routing and forwarding: ·         Specifying the longest prefix match principle ·         Configuring IPv6 multicast load splitting ·         Configuring an IPv6 multicast forwarding boundary ·         Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN

 

Enabling IPv6 multicast routing

Enable IPv6 multicast routing before you configure any Layer 3 IPv6 multicast functionality in the public network.

To enable IPv6 multicast routing:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Enable IPv6 multicast routing and enter IPv6 MRIB view.	ipv6 multicast routing	By default, IPv6 multicast routing is disabled.

 

Configuring IPv6 multicast routing and forwarding

Before you configure IPv6 multicast routing and forwarding, complete the following tasks:

·          Configure an IPv6 unicast routing protocol so that all devices in the domain can interoperate at the network layer.

·          Configure IPv6 PIM-DM or IPv6 PIM-SM.

Specifying 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."

To specify the longest prefix match principle for RPF route selection:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Enter IPv6 MRIB view.	ipv6 multicast routing	N/A
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

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.

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

To configure IPv6 multicast load splitting:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Enter IPv6 MRIB view.	ipv6 multicast routing	N/A
3.       Configure IPv6 multicast load splitting.	load-splitting {source | source-group }	By default, IPv6 multicast load splitting is disabled. This command does not take effect on IPv6 BIDIR-PIM.

 

Configuring an IPv6 multicast forwarding boundary

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.

 

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

 

To configure an IPv6 multicast forwarding boundary:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Enter interface view.	interface interface-type interface-number	N/A
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.

 

Enabling 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 the super VLAN and sub-VLANs, see Layer 2—LAN Switching Configuration Guide.

To enable IPv6 multicast forwarding between sub-VLANs that are associated with a super VLAN:

 

Step	Command	Remarks
1.       Enter system view.	system-view	N/A
2.       Enter VLAN interface view.	interface vlan-interface interface-number	N/A
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.       Delete all IPv6 multicast forwarding entries with super VLAN interface as the incoming interface.	reset ipv6 multicast forwarding-table { { ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface { interface-type interface-number } } * | all }	N/A

 

Displaying and maintaining 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 DF information.	display ipv6 multicast forwarding df-info [ ipv6-rp-address ] [ verbose ] [ 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 information about the DF list in the IPv6 multicast forwarding table.	display ipv6 multicast forwarding-table df-list [ ipv6-group-address ] [ verbose ] [ slot slot-number ]
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 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.