Contents

Configuring IPv6 multicast routing and forwarding· 1

About IPv6 multicast routing and forwarding· 1

RPF check mechanism·· 1

IPv6 mtrace· 3

Restrictions and guidelines: IPv6 multicast routing and forwarding configuration· 3

IPv6 multicast routing and forwarding tasks at a glance· 3

Prerequisites for IPv6 multicast routing and forwarding· 4

Enabling IPv6 multicast routing· 4

Configuring static IPv6 multicast routes· 4

Specifying the longest prefix match principle· 5

Configuring IPv6 multicast load splitting· 5

Configuring an IPv6 multicast forwarding boundary· 5

Using mtrace2 to trace an IPv6 multicast path· 6

Display and maintenance commands for IPv6 multicast routing and forwarding· 6

IPv6 multicast routing and forwarding configuration examples· 8

Example: Changing an RPF route· 8

Example: Creating an RPF route· 10

 

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 "IPv6 PIM overview."

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

 

‌

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.

Restrictions and guidelines: IPv6 multicast routing and forwarding configuration

During ISSU on a multichassis IRF, if the incoming interface of Layer 3 multicast traffic contains non-local member ports, Layer 3 multicast traffic interruption might occur when the device is rebooting.

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.) Configuring static IPv6 multicast routes

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

4.     (Optional.) Configuring IPv6 multicast load splitting

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

6.     (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 this task

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.

Configuring static IPv6 multicast routes

About this task

When configuring a static IPv6 multicast route for an IPv6 multicast source, you can specify an RPF interface or an RPF neighbor for the IPv6 multicast traffic from that source.

Restrictions: Software version and feature compatibility

This feature is supported only in Release 6522 and later.

Restrictions and guidelines

Static IPv6 multicast routes take effect only on the IPv6 multicast devices on which they are configured, and will not be broadcast or redistributed to other devices.

Procedure

1.     Enter system view.

system-view

2.     Configure a static multicast route.

ipv6 rpf-route-static ipv6-source-address prefix-length { rpf-nbr-address | interface-type interface-number } [ preference preference ]

3.     (Optional.) Delete all static IPv6 multicast routes.

delete ipv6 rpf-route-static

To delete a single static IPv6 multicast route, use the undo ip rpf-route-static command.

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 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 this task

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 this task

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.

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 static IPv6 multicast routing entries.	display ipv6 multicast routing-table static [ ipv6-source-address [ prefix-length ] ]
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.

 

IPv6 multicast routing and forwarding configuration examples

Example: Changing an RPF route

Network configuration

As shown in Figure 2:

·     IPv6 PIM-DM runs on the network.

·     All switches on the network support IPv6 multicast.

·     Switch A, Switch B, and Switch C run OSPFv3.

·     Typically, the receiver host can receive the IPv6 multicast data from the source through the path: Switch A to Switch B, which is the same as the unicast route.

Configure the switches so that the IPv6 multicast data from the source travels to the receiver along the following path: Switch A to Switch C to Switch B. This path is different from the unicast route.

Figure 2 Network diagram

 

Prerequisites

1.     Assign an IP address and prefix length for each interface, as shown in Figure 2.

2.     Configure OSPFv3 on the switches in the IPv6 PIM-DM domain.

Procedure

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

# On Switch B, enable IPv6 multicast routing.

<SwitchB> system-view

[SwitchB] ipv6 multicast routing

[SwitchB-mrib6] quit

# Enable MLD on the receiver-side interface VLAN-interface 100.

[SwitchB] interface vlan-interface 100

[SwitchB-Vlan-interface100] mld enable

[SwitchB-Vlan-interface100] quit

# Enable IPv6 PIM-DM on the other interfaces.

[SwitchB] interface vlan-interface 101

[SwitchB-Vlan-interface101] ipv6 pim dm

[SwitchB-Vlan-interface101] quit

[SwitchB] interface vlan-interface 102

[SwitchB-Vlan-interface102] ipv6 pim dm

[SwitchB-Vlan-interface102] quit

 

# On Switch A, enable IPv6 multicast routing.

<SwitchA> system-view

[SwitchA] ipv6 multicast routing

[SwitchA-mrib6] quit

# Enable IPv6 PIM-DM on each interface.

[SwitchA] interface vlan-interface 200

[SwitchA-Vlan-interface200] ipv6 pim dm

[SwitchA-Vlan-interface200] quit

[SwitchA] interface vlan-interface 102

[SwitchA-Vlan-interface102] ipv6 pim dm

[SwitchA-Vlan-interface102] quit

[SwitchA] interface vlan-interface 103

[SwitchA-Vlan-interface103] ipv6 pim dm

[SwitchA-Vlan-interface103] quit

 

# Enable IPv6 multicast routing and IPv6 PIM-DM on Switch C in the same way Switch A is configured. (Details not shown.)

2.     Display RPF information for the source on Switch B.

[SwitchB] display ipv6 multicast rpf-info 500::100

 RPF information about source 500::100:

     RPF interface: Vlan-interface102, RPF neighbor: 300::2

     Referenced prefix/prefix length: 500::/64

     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 Switch B is contributed by a unicast routing protocol and the RPF neighbor is Switch A.

3.     On Switch B, configure a static IPv6 multicast route to the source and specify Switch C as the RPF neighbor.

[SwitchB] ipv6 rpf-route-static 500::100 64 200::2

 

Verifying the configuration

# Display RPF information for the source on Switch B.

[SwitchB] display ipv6 multicast rpf-info 500::100

 RPF information about source 500::100:

     RPF interface: Vlan-interface101, RPF neighbor: 200::2

     Referenced prefix/prefix length: 500::/64

     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 Switch B is the configured static IPv6 multicast route.

·     The RPF neighbor of Switch B is Switch C.

Example: Creating an RPF route

Network configuration

As shown in Figure 3:

·     IPv6 PIM-DM runs on the network.

·     All switches on the network support IP multicast.

·     Switch B and Switch C run OSPFv3, and have no unicast routes to Switch A.

·     Typically, the receiver host receives the IPv6 multicast data from the source 1 in the OSPFv3 domain.

Configure the switches so that the receiver host can receive IPv6 multicast data from Source 2, which is outside the OSPFv3 domain.

Figure 3 Network diagram

 

Prerequistes

1.     Assign an IP address and subnet mask for each interface, as shown in Figure 3.

2.     Configure OSPFv3 on Switch B and Switch C.

Procedure

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

# On Switch C, enable IPv6 multicast routing.

<SwitchC> system-view

[SwitchC] ipv6 multicast routing

[SwitchC-mrib6] quit

# Enable MLD on the receiver-side interface VLAN-interface 100.

[SwitchC] interface vlan-interface 100

[SwitchC-Vlan-interface100] mld enable

[SwitchC-Vlan-interface100] quit

# Enable IPv6 PIM-DM on VLAN-interface 101.

[SwitchC] interface vlan-interface 101

[SwitchC-Vlan-interface101] ipv6 pim dm

[SwitchC-Vlan-interface101] quit

 

# On Switch A, enable IPv6 multicast routing.

<SwitchA> system-view

[SwitchA] ipv6 multicast routing

[SwitchA-mrib6] quit

# Enable IPv6 PIM-DM on each interface.

[SwitchA] interface vlan-interface 300

[SwitchA-Vlan-interface300] ipv6 pim dm

[SwitchA-Vlan-interface300] quit

[SwitchA] interface vlan-interface 102

[SwitchA-Vlan-interface102] ipv6 pim dm

[SwitchA-Vlan-interface102] quit

 

# Enable IPv6 multicast routing and IPv6 PIM-DM on Switch B in the same way Switch A is configured. (Details not shown.)

2.     Display RPF information for Source 2 on Switch B and Switch C.

[SwitchB] display ipv6 multicast rpf-info 500::100

[SwitchC] display ipv6 multicast rpf-info 500::100

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

3.     Configure a static IPv6 multicast route:

# Configure a static IPv6 multicast route on Switch B and specify Switch A as its RPF neighbor to Source 2.

[SwitchB] ipv6 rpf-route-static 500::100 64 300::2

 

# Configure a static IPv6 multicast route on Switch C and specify Switch B as its RPF neighbor to Source 2.

[SwitchC] ipv6 rpf-route-static 500::100 64 200::2

 

Verifying the configuration

# Display RPF information for Source 2 on Switch B.

[SwitchB] display ipv6 multicast rpf-info 500::100

 RPF information about source 50::100:

     RPF interface: Vlan-interface102, RPF neighbor: 300::2

     Referenced prefix/prefix length: 500::/64

     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 Switch C.

[SwitchC] display ipv6 multicast rpf-info 500::100

 RPF information about source 500::100:

     RPF interface: Vlan-interface101, RPF neighbor: 200::2

     Referenced prefix/prefix length: 500::/64

     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 Switch B and Switch C. These RPF routes are the configured static IPv6 multicast routes.