Configuring IPv6 multicast routing and forwarding· 1

Overview·· 1

RPF check mechanism·· 1

IPv6 multicast forwarding across IPv6 unicast subnets 3

Configuration task list 3

Enabling IPv6 multicast routing· 4

Configuring IPv6 multicast routing and forwarding· 4

Specifying the longest prefix match principle· 4

Configuring IPv6 multicast load splitting· 4

Configuring an IPv6 multicast forwarding boundary· 5

Configuring IPv6 static multicast MAC address entries 5

Configuring IPv6 multicast forwarding among sub-VLANs of a super VLAN·· 6

Displaying and maintaining IPv6 multicast routing and forwarding· 7

Configuration examples 8

IPv6 multicast forwarding over a GRE tunnel 8

 

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.

The term "interface" in this chapter collectively refers to VLAN interfaces and Layer 3 Ethernet interfaces. You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see Layer 2—LAN Switching Configuration Guide).

RPF check mechanism

An IPv6 multicast routing protocol relies on the existing IPv6 unicast routing information in creating IPv6 multicast routing entries. When creating IPv6 multicast routing table entries, an IPv6 multicast routing protocol uses the reverse path forwarding (RPF) check mechanism to ensure IPv6 multicast data delivery along the correct path. The RPF check mechanism also helps avoid data loops caused by various reasons.

RPF check process

Based on the IPv6 unicast routing table, a router performs the RPF check on an IPv6 multicast packet as follows:

1.     The router chooses an optimal unicast route back to the packet source from the IPv6 unicast routing table. This optimal route is the RPF route for the packet. The outgoing interface of the route is the RPF interface, and the next hop is the RPF neighbor.

2.     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.

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

·     For a packet that travels along the SPT from the multicast source to the receivers or the RP, the packet source for RPF check is the multicast source.

·     For a packet that travels along the RPT from the RP to the receivers, the packet source for RPF check is the RP.

·     For a packet that travels along the source-side RPT from the multicast source to the RP, the packet source for RPF check is the RP.

·     For a bootstrap message from the BSR, the packet source for RPF check is the BSR.

For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see "Configuring IPv6 PIM."

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) forwarding entry. After the router receives another (S, G) packet, it looks up its IPv6 multicast forwarding table for the matching (S, G) entry:

·     If a match is not 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 router forwards the packet out of all outgoing interfaces.

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

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

·     If a match is found but the receiving interface is not the incoming interface of the forwarding entry, 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. 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 in the network and IPv6 multicast packets travel along the SPT from the multicast source to the receivers. The IPv6 multicast forwarding table on Switch C contains the (S, G) entry, with VLAN-interface 20 as the RPF interface.

·     If an IPv6 multicast packet arrives at Switch C on VLAN-interface 20, the receiving interface is the incoming interface of the (S, G) entry. Switch C forwards the packet out of all outgoing interfaces.

·     If an IPv6 multicast packet arrives at Switch C on VLAN-interface, the receiving interface is not the incoming interface of the (S, G) entry. Switch C searches its IPv6 unicast routing table and finds that the outgoing interface to the source 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 Switch C discards the packet.

IPv6 multicast forwarding across IPv6 unicast subnets

Routers forward the IPv6 multicast data from an IPv6 multicast source hop by hop along the forwarding tree, but some routers might not support IPv6 multicast protocols in a network. When the IPv6 multicast data is forwarded to a router that does not support IPv6 multicast, the forwarding path is blocked. In this case, you can enable IPv6 multicast data forwarding across the IPv6 unicast subnets by establishing a tunnel between the routers at both ends of the IPv6 unicast subnets.

Figure 2 IPv6 multicast data transmission through a tunnel

 

As shown in Figure 2, a tunnel is established between the multicast routers Switch A and Switch B. Switch A encapsulates the IPv6 multicast data in unicast IPv6 packets, and forwards them to Switch B across the tunnel through unicast routers. Then, Switch B strips off the unicast IPv6 header and continues to forward the IPv6 multicast data down toward the receivers.

Configuration task list

Tasks at a glance
(Required.) Enabling IPv6 multicast routing
(Optional.) Configuring IPv6 multicast routing and forwarding ·     (Optional.) Specifying the longest prefix match principle ·     (Optional.) Configuring IPv6 multicast load splitting ·     (Optional.) Configuring an IPv6 multicast forwarding boundary ·     (Optional.) Configuring IPv6 static multicast MAC address entries ·     (Optional.) Configuring IPv6 multicast forwarding among 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 or VPN instance.

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 [ vpn-instance vpn-instance-name ]	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 IPv6 multicast router 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:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter IPv6 MRIB view.	ipv6 multicast routing [ vpn-instance vpn-instance-name ]	N/A
3.     Specify the longest prefix match principle.	longest-match	By default, the route preference principle is used.

 

Configuring IPv6 multicast load splitting

You can enable the IPv6 multicast router 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 [ vpn-instance vpn-instance-name ]	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 nor forward IPv6 multicast packets for the group.

 

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 the interface as an IPv6 multicast forwarding boundary for an IPv6 multicast group range.	ipv6 multicast boundary { ipv6-group-address prefix-length | scope { scope-id | admin-local | global | organization-local | site-local } }	By default, the interface is not configured as an IPv6 multicast forwarding boundary for any group range.

 

Configuring IPv6 static multicast MAC address entries

In Layer-2 multicast, a Layer-2 IPv6 multicast protocol (such as MLD snooping) can dynamically add IPv6 multicast MAC address entries. Or, you can manually configure IPv6 multicast MAC address entries.

 

TIP: ·     You do not need to enable IPv6 multicast routing before this configuration. ·     The IPv6 multicast MAC address that can be configured in a MAC address entry must be unused. A multicast MAC address is the MAC address in which the least significant bit of the most significant octet is 1.

 

You can configure IPv6 static multicast MAC address entries on the specified interfaces in system view, or on the current interface in interface view.

To configure an IPv6 static multicast MAC address entry in system view:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Configure a static multicast MAC address entry.	mac-address multicast mac-address interface interface-list vlan vlan-id	By default, static multicast MAC address entries do not exist.

 

To configure an IPv6 static multicast MAC address entry in interface view:

 

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter Layer 2 Ethernet interface/Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3.     Configure a static multicast MAC address entry.	mac-address multicast mac-address vlan vlan-id	By default, static multicast MAC address entries do not exist.

 

Configuring IPv6 multicast forwarding among 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 configure multicast forwarding among sub-VLANs of 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.     Configure IPv6 multicast forwarding among sub-VLANs of a super VLAN.	ipv6 multicast forwarding supervlan community	By default, IPv6 multicast data cannot be forwarded among sub-VLANs of a super VLAN.
4.     Clear all IPv6 multicast forwarding entries with super VLAN interface as the incoming interface.	reset ipv6 multicast [ vpn-instance vpn-instance-name ] 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 IPv6 static multicast MAC address entries.	display mac-address [ mac-address [ vlan vlan-id ] | [ multicast ] [ vlan vlan-id ] [ count ] ]
Display information about interfaces maintained by the IPv6 MRIB.	display ipv6 mrib [ vpn-instance vpn-instance-name ] interface [ interface-type interface-number ]
Display IPv6 multicast boundary information.	display ipv6 multicast [ vpn-instance vpn-instance-name ] boundary { group [ ipv6-group-address [ prefix-length ] ] | scope [ scope-id ] } [ interface interface-type interface-number ]
Display information about the DF for IPv6 multicast forwarding.	display ipv6 multicast [ vpn-instance vpn-instance-name ] forwarding df-info [ ipv6-rp-address ] [ verbose ] [ slot slot-number ]
Display statistics for IPv6 multicast forwarding events.	display ipv6 multicast [ vpn-instance vpn-instance-name ] forwarding event [ slot slot-number ]
Display IPv6 multicast forwarding entries.	display ipv6 multicast [ vpn-instance vpn-instance-name ] 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 [ vpn-instance vpn-instance-name ] forwarding-table df-list [ ipv6-group-address ] [ verbose ] [ slot slot-number ]
Display IPv6 multicast routing entries.	display ipv6 multicast [ vpn-instance vpn-instance-name ] 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 the RPF route information for an IPv6 multicast source.	display ipv6 multicast [ vpn-instance vpn-instance-name ] rpf-info ipv6-source-address [ ipv6-group-address ]
Clear statistics for IPv6 multicast forwarding events.	reset ipv6 multicast [ vpn-instance vpn-instance-name ] forwarding event
Clear IPv6 multicast forwarding entries.	reset ipv6 multicast [ vpn-instance vpn-instance-name ] 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 [ vpn-instance vpn-instance-name ] routing-table { { ipv6-source-address [ prefix-length ] | ipv6-group-address [ prefix-length ] | incoming-interface interface-type interface-number } * | all }

 

NOTE: When you delete an IPv6 multicast routing entry, the associated IPv6 multicast forwarding entry is also deleted. When you delete an IPv6 multicast forwarding entry, the associated IPv6 multicast routing entry is also deleted.

 

Configuration examples

IPv6 multicast forwarding over a GRE tunnel

Network requirements

As shown in Figure 3:

·     IPv6 multicast routing and IPv6 PIM-DM are enabled on Switch A and Switch C.

·     Switch B does not support IPv6 multicast.

·     Switch A, Switch B, and Switch C run OSPFv3. The source-side interface VLAN-interface 100 on Switch A does not run OSPFv3.

Configure the switches so that the receiver host can receive the IPv6 multicast data from the source.

Figure 3 Network diagram

Configuration procedure

1.     Assign an IPv6 address and prefix length to each interface as shown in Figure 3. (Details not shown.)

2.     Configure OSPFv3 on all the switches. Do not enable OSPFv3 on the source-side interface VLAN-interface 100 on Switch A. (Details not shown.)

3.     Configure a GRE tunnel:

# Create service loopback group 1 on Switch A and specify its service type as Tunnel.

<SwitchA> system-view

[SwitchA] service-loopback group 1 type tunnel

# Add FortyGigE 1/1/3 of Switch A to service loopback group 1. FortyGigE 1/1/3 does not belong to VLAN 100 or VLAN 101.

[SwitchA] interface fortygige 1/1/3

[SwitchA-FortyGigE1/1/3] port service-loopback group 1

[SwitchA-FortyGigE1/1/3] quit

# Create an IPv6 GRE tunnel interface Tunnel 0 on Switch A.

[SwitchA] interface tunnel 0 mode gre ipv6

# Assign an IPv6 address to interface Tunnel 0 on Switch A, and specify its source and destination addresses.

[SwitchA-Tunnel0] ipv6 address 5001::1 64

[SwitchA-Tunnel0] source 2001::1

[SwitchA-Tunnel0] destination 3001::2

[SwitchA-Tunnel0] quit

# Create service loopback group 1 on Switch C and specify its service type as Tunnel.

<SwitchC> system-view

[SwitchC] service-loopback group 1 type tunnel

# Add FortyGigE 1/1/3 of Switch C to service loopback group 1. FortyGigE 1/1/3 does not belong to VLAN 200 or VLAN 102.

[SwitchC] interface fortygige 1/1/3

[SwitchC-FortyGigE1/1/3] port service-loopback group 1

[SwitchC-FortyGigE1/1/3] quit

# Create an IPv6 GRE tunnel interface Tunnel 0 on Switch C.

[SwitchC] interface tunnel 0 mode gre ipv6

# Assign an IPv6 address to interface Tunnel 0 on Switch C, and specify its source and destination addresses.

[SwitchC-Tunnel0] ipv6 address 5001::2 64

[SwitchC-Tunnel0] source 3001::2

[SwitchC-Tunnel0] destination 2001::1

[SwitchC-Tunnel0] quit

4.     Enable IPv6 multicast routing, IPv6 PIM-DM, and MLD:

# On Switch A, enable IPv6 multicast routing, and enable IPv6 PIM-DM on each interface.

[SwitchA] ipv6 multicast routing

[SwitchA-mrib6] quit

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] ipv6 pim dm

[SwitchA-Vlan-interface100] quit

[SwitchA] interface vlan-interface 101

[SwitchA-Vlan-interface101] ipv6 pim dm

[SwitchA-Vlan-interface101] quit

[SwitchA] interface tunnel 0

[SwitchA-Tunnel0] ipv6 pim dm

[SwitchA-Tunnel0] quit

# On Switch C, enable IPv6 multicast routing globally.

[SwitchC] ipv6 multicast routing

[SwitchC-mrib6] quit

# Enable MLD on VLAN-interface 200 (the interface that connects to the receiver host).

[SwitchC] interface vlan-interface 200

[SwitchC-Vlan-interface200] mld enable

[SwitchC-Vlan-interface200] quit

# Enable IPv6 PIM-DM on the other interfaces.

[SwitchC] interface vlan-interface 102

[SwitchC-Vlan-interface102] ipv6 pim dm

[SwitchC-Vlan-interface102] quit

[SwitchC] interface tunnel 0

[SwitchC-Tunnel0] ipv6 pim dm

[SwitchC-Tunnel0] quit

5.     On Switch C, configure an IPv6 static route and specify the RPF neighbor toward the source as interface Tunnel 0 on Switch A.

[SwitchC] ipv6 route-static 1001::1 64 tunnel 0

Verifying the configuration

# Send an MLD report from the Receiver to join the IPv6 multicast group FF1E::101. (Details not shown.)

# Send IPv6 multicast data from Source to the IPv6 multicast group FF1E::101. (Details not shown.)

# Display IPv6 PIM routing table information on Switch C.

[SwitchC] display ipv6 pim routing-table

 Total 1 (*, G) entry; 1 (S, G) entry

 

 (*, FF1E::101)

     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: Vlan-interface200

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

 

 (1001::100, FF1E::101)

     Protocol: pim-dm, Flag: ACT

     UpTime: 00:06:14

     Upstream interface: Tunnel0

         Upstream neighbor: FE80::A01:101:1

         RPF prime neighbor: FE80::A01:101:1

     Downstream interface(s) information:

     Total number of downstreams: 1

         1: Vlan-interface200

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

The output shows that Switch A is the RPF neighbor of Switch C and the IPv6 multicast data from Switch A is delivered over a GRE tunnel to Switch C.