Protocol Independent Multicast for IPv6 (IPv6 PIM) provides IPv6 multicast forwarding by leveraging static routes or IPv6 unicast routing tables generated by any IPv6 unicast routing protocol, such as RIPng, OSPFv3, IS-ISv6, or BGP4+. IPv6 PIM uses an IPv6 unicast routing table to perform reverse path forwarding (RPF) check to implement IPv6 multicast forwarding. Independent of the IPv6 unicast routing protocols running on the device, IPv6 multicast routing can be implemented as long as the corresponding IPv6 multicast routing entries are created through IPv6 unicast routes. IPv6 PIM uses the reverse path forwarding (RPF) mechanism to implement IPv6 multicast forwarding. When an IPv6 multicast packet arrives on an interface of the device, it is subject to an RPF check. If the RPF check succeeds, the device creates the corresponding routing entry and forwards the packet; if the RPF check fails, the device discards the packet. For more information about RPF, refer to IPv6 Multicast Routing and Forwarding Configuration in the IP Multicast Volume.

Based on the implementation mechanism, IPv6 PIM falls into two modes:

l Protocol Independent Multicast–Dense Mode for IPv6 (IPv6 PIM-DM), and

l Protocol Independent Multicast–Sparse Mode for IPv6 (IPv6 PIM-SM).

To facilitate description, a network comprising IPv6 PIM–supporting routers is referred to as an “IPv6 PIM domain” in this document.

Introduction to IPv6 PIM-DM

IPv6 PIM-DM is a type of dense mode IPv6 multicast protocol. It uses the “push mode” for IPv6 multicast forwarding, and is suitable for small-sized networks with densely distributed IPv6 multicast members.

The basic implementation of IPv6 PIM-DM is as follows:

l IPv6 PIM-DM assumes that at least one IPv6 multicast group member exists on each subnet of a network, and therefore IPv6 multicast data is flooded to all nodes on the network. Then, branches without IPv6 multicast forwarding are pruned from the forwarding tree, leaving only those branches that contain receivers. This “flood and prune” process takes place periodically, that is, pruned branches resume IPv6 multicast forwarding when the pruned state times out and then data is re-flooded down these branches, and then are pruned again.

l When a new receiver on a previously pruned branch joins an IPv6 multicast group, to reduce the join latency, IPv6 PIM-DM uses the graft mechanism to resume IPv6 multicast data forwarding to that branch.

Generally speaking, the IPv6 multicast forwarding path is a source tree, namely a forwarding tree with the IPv6 multicast source as its “root” and IPv6 multicast group members as its “leaves”. Because the source tree is the shortest path from the IPv6 multicast source to the receivers, it is also called shortest path tree (SPT).

How IPv6 PIM-DM Works

The working mechanism of IPv6 PIM-DM is summarized as follows:

l Neighbor discovery

l SPT establishment

l Graft

l Assert

Neighbor discovery

In an IPv6 PIM domain, a PIM router discovers IPv6 PIM neighbors, maintains IPv6 PIM neighboring relationships with other routers, and builds and maintains SPTs by periodically multicasting IPv6 PIM hello messages (hereinafter referred to as “hello messages”) to all other IPv6 PIM routers.

Every IPv6 PIM enabled interface on a router sends hello messages periodically, and thus learns the IPv6 PIM neighboring information pertinent to the interface.

SPT establishment

The process of constructing an SPT is the “flood and prune” process.

1) In an IPv6 PIM-DM domain, an IPv6 multicast source first floods IPv6 multicast packets when it sends IPv6 multicast data to IPv6 multicast group G: The packet is subject to an RPF check. If the packet passes the RPF check, the router creates an (S, G) entry and forwards the packet to all downstream nodes in the network. In the flooding process, an (S, G) entry is created on all the routers in the IPv6 PIM-DM domain.

2) Then, nodes without downstream receivers are pruned: A router having no down stream receivers sends a prune message to the upstream node to notify the upstream node to delete the corresponding interface from the outgoing interface list in the (S, G) entry and stop forwarding subsequent packets addressed to that IPv6 multicast group down to this node.

l An (S, G) entry contains the multicast source address S, IPv6 multicast group address G, outgoing interface list, and incoming interface.

l For a given IPv6 multicast stream, the interface that receives the IPv6 multicast stream is referred to as “upstream”, and the interfaces that forward the IPv6 multicast stream are referred to as “downstream”.

A prune process is first initiated by a leaf router. As shown in Figure 1-1, a router without any receiver attached to it (the router connected with Host A, for example) sends a prune message, and this prune process goes on until only necessary branches are left in the IPv6 PIM-DM domain. These branches constitute the SPT.

Figure 1-1 SPT establishment in an IPv6 PIM-DM domain

The “flood and prune” process takes place periodically. A pruned state timeout mechanism is provided. A pruned branch restarts multicast forwarding when the pruned state times out and then is pruned again when it no longer has any multicast receiver.

Pruning has a similar implementation in IPv6 PIM-SM.

Graft

When a host attached to a pruned node joins an IPv6 multicast group, to reduce the join latency, IPv6 PIM-DM uses the graft mechanism to resume IPv6 multicast data forwarding to that branch. The process is as follows:

1) The node that needs to receive IPv6 multicast data sends a graft message toward its upstream node, as a request to join the SPT again.

2) Upon receiving this graft message, the upstream node puts the interface on which the graft was received into the forwarding state and responds with a graft-ack message to the graft sender.

3) If the node that sent a graft message does not receive a graft-ack message from its upstream node, it will keep sending graft messages at a configurable interval until it receives an acknowledgment from its upstream node.

Assert

The assert mechanism is used to shutoff duplicate IPv6 multicast flows onto the same multi-access network, where more than one multicast routers exists, by electing a unique IPv6 multicast forwarder on the multi-access network.

Figure 1-2 Assert mechanism

As shown in Figure 1-2, after Router A and Router B receive an (S, G) IPv6 multicast packet from the upstream node, they both forward the packet to the local subnet. As a result, the downstream node Router C receives two identical multicast packets, and both Router A and Router B, on their own local interface, receive a duplicate IPv6 multicast packet forwarded by the other. Upon detecting this condition, both routers send an assert message to all IPv6 PIM routers through the interface on which the packet was received. The assert message contains the following information: the multicast source address (S), the multicast group address (G), and the preference and metric of the IPv6 unicast route to the source. By comparing these parameters, either Router A or Router B becomes the unique forwarder of the subsequent (S, G) IPv6 multicast packets on the multi-access subnet. The comparison process is as follows:

1) The router with a higher IPv6 unicast route preference to the source wins;

2) If both routers have the same IPv6 unicast route preference to the source, the router with a smaller metric to the source wins;

3) If there is a tie in the route metric to the source, the router with a higher IPv6 link-local address wins.

Introduction to IPv6 PIM-SM

IPv6 PIM-DM uses the “flood and prune” principle to build SPTs for IPv6 multicast data distribution. Although an SPT has the shortest path, it is built with a low efficiency. Therefore the PIM-DM mode is not suitable for large-and medium-sized networks.

IPv6 PIM-SM is a type of sparse mode IPv6 multicast protocol. It uses the “pull mode” for IPv6 multicast forwarding, and is suitable for large- and medium-sized networks with sparsely and widely distributed IPv6 multicast group members.

The basic implementation of IPv6 PIM-SM is as follows:

l IPv6 PIM-SM assumes that no hosts need to receive IPv6 multicast data. In the IPv6 PIM-SM mode, routers must specifically request a particular IPv6 multicast stream before the data is forwarded to them. The core task for IPv6 PIM-SM to implement IPv6 multicast forwarding is to build and maintain rendezvous point trees (RPTs). An RPT is rooted at a router in the IPv6 PIM domain as the common node, or rendezvous point (RP), through which the IPv6 multicast data travels along the RPT and reaches the receivers.

l When a receiver is interested in the IPv6 multicast data addressed to a specific IPv6 multicast group, the router connected to this receiver sends a join message to the RP corresponding to that IPv6 multicast group. The path along which the message goes hop by hop to the RP forms a branch of the RPT.

l When an IPv6 multicast source sends IPv6 multicast streams to an IPv6 multicast group, the source-side designated router (DR) first registers the multicast source with the RP by sending register messages to the RP by unicast until it receives a register-stop message from the RP. The arrival a register message at the RP triggers the establishment of an SPT. Then, the IPv6 multicast source sends subsequent IPv6 multicast packets along the SPT to the RP. Upon reaching the RP, the IPv6 multicast packet is duplicated and delivered to the receivers along the RPT.

IPv6 multicast traffic is duplicated only where the distribution tree branches, and this process automatically repeats until the IPv6 multicast traffic reaches the receivers.

How IPv6 PIM-SM Works

The working mechanism of IPv6 PIM-SM is summarized as follows:

l Neighbor discovery

l DR election

l RP discovery

l Embedded RP

l RPT establishment

l IPv6 Multicast source registration

l Switchover to SPT

l Assert

Neighbor discovery

IPv6 PIM-SM uses the similar neighbor discovery mechanism as IPv6 PIM-DM does. Refer to Neighbor discovery.

DR election

IPv6 PIM-SM also uses hello messages to elect a DR for a multi-access network (such as a LAN). The elected DR will be the only IPv6 multicast forwarder on this multi-access network.

In the case of a multi-access network, a DR must be elected, no matter this network connects to IPv6 multicast sources or to receivers. The DR at the receiver side sends join messages to the RP; the DR at the IPv6 multicast source side sends register messages to the RP.

l A DR is elected on a multi-access subnet by means of comparison of the priorities and IPv6 link-local addresses carried in hello messages.

l MLD must be enabled on a device that acts as a receiver-side DR before receivers attached to this device can join IPv6 multicast groups through this DR.

For details about MLD, refer to MLD Configuration in the IP Multicast Volume.

Figure 1-3 DR election

As shown in Figure 1-3, the DR election process is as follows:

1) Routers on the multi-access network send hello messages to one another. The hello messages contain the router priority for DR election. The router with the highest DR priority will become the DR.

2) In the case of a tie in the router priority, or if any router in the network does not support carrying the DR-election priority in hello messages, The router with the highest IPv6 link-local address will win the DR election.

When the DR works abnormally, a timeout in receiving hello message triggers a new DR election process among the other routers.

RP discovery

The RP is the core of an IPv6 PIM-SM domain. For a small-sized, simple network, one RP is enough for forwarding IPv6 multicast information throughout the network, and the position of the RP can be statically specified on each router in the IPv6 PIM-SM domain. In most cases, however, an IPv6 PIM-SM network covers a wide area and a huge amount of IPv6 multicast traffic needs to be forwarded through the RP. To lessen the RP burden and optimize the topological structure of the RPT, multiple candidate RPs (C-RPs) can be configured in an IPv6 PIM-SM domain, among which an RP is dynamically elected through the bootstrap mechanism. Each elected RP serves a different multicast group range. For this purpose, a bootstrap router (BSR) must be configured. The BSR serves as the administrative core of the IPv6 PIM-SM domain. An IPv6 PIM-SM domain can have only one BSR, but can have multiple candidate-BSRs (C-BSRs). Once the BSR fails, a new BSR is automatically elected from the C-BSRs to avoid service interruption.

l An RP can serve IPv6 multiple multicast groups or all IPv6 multicast groups. Only one RP can serve a given IPv6 multicast group at a time.

l A device can server as a C-RP and a C-BSR at the same time.

As shown in the figure below, each C-RP periodically unicasts its advertisement messages (C-RP-Adv messages) to the BSR. A C-RP-Adv message contains the address of the advertising C-RP and the IPv6 multicast group range it serves. The BSR collects these advertisement messages and chooses the appropriate C-RP information for each multicast group to form an RP-set, which is a database of mappings between IPv6 multicast groups and RPs. The BSR then encapsulates the RP-set in the bootstrap messages it periodically originates and floods the bootstrap messages to the entire IPv6 PIM-SM domain.

Figure 1-4 BSR and C-RPs

Based on the information in the RP-sets, all routers in the network can calculate the location of the corresponding RPs based on the following rules:

1) The C-RP with the highest priority wins.

2) If all the C-RPs have the same priority, their hash values are calculated through the hashing algorithm. The C-RP with the largest hash value wins.

3) If all the C-RPs have the same priority and hash value, the C-RP has the highest IP address wins.

The hashing algorithm used for RP calculation is: Value (G, M, C_i) = (1103515245 * ( (1103515245 * (G & M) + 12345) XOR C_i) + 12345) mod 2³¹. The table below gives the meanings of the values in this algorithm.

Table 1-1 Values in the hashing algorithm

Value	Description
Value	Hash value
G	The digest from the exclusive-or (XOR) operation between the 32-bit segments of the IPv6 multicast group address. For example, if the IPv6 multicast address is FF0E:C20:1A3:63::101, G = 0xFF0E0C20 XOR 0x01A30063 XOR 0x00000000 XOR 0x00000101
M	Hash mask length
C_i	The digest from the exclusive-or (XOR) operation between the 32-bit segments of the C-RP IPv6 address. For example, if the IPv6 address of the C-RP is 3FFE:B00:C18:1::10, C_i = 0x3FFE0B00 XOR 0x0C180001 XOR 0x00000000 XOR 0x00000010
&	Logical operator of “and”
XOR	Logical operator of “exclusive-or”
mod	Modulo operator, which gives the remainder of an integer division

Embedded RP

The Embedded RP mechanism allows a router to resolve the RP address from an IPv6 multicast address so that the IPv6 multicast group is mapped to an RP, which can take the place of the statically configured RP or the RP dynamically calculated based on the BSR mechanism. The DR does not need to know the RP address beforehand. The specific process is as follows.

l At the receiver side:

1) A receiver host initiates an MLD report to announce its joining an IPv6 multicast group.

2) Upon receiving the MLD report, the receiver-side DR resolves the RP address embedded in the IPv6 multicast address, and sends a join message to the RP.

l At the IPv6 multicast source side:

3) The IPv6 multicast source sends IPv6 multicast traffic to the IPv6 multicast group.

4) The source-side DR resolves the RP address embedded in the IPv6 multicast address, and sends a register message to the RP.

RPT establishment

Figure 1-5 RPT establishment in an IPv6 PIM-SM domain

As shown in Figure 1-5, the process of building an RPT is as follows:

1) When a receiver joins IPv6 multicast group G, it uses an MLD report message to inform the directly connected DR.

2) Upon getting the IPv6 multicast group G’s receiver information, the DR sends a join message, which is hop by hop forwarded to the RP corresponding to the multicast group.

3) The routers along the path from the DR to the RP form an RPT branch. Each router on this branch generates a (*, G) entry in its forwarding table. The * means any IPv6 multicast source. The RP is the root, while the DRs are the leaves, of the RPT.

The IPv6 multicast data addressed to the IPv6 multicast group G flows through the RP, reaches the corresponding DR along the established RPT, and finally is delivered to the receiver.

When a receiver is no longer interested in the IPv6 multicast data addressed to a multicast group G, the directly connected DR sends a prune message, which goes hop by hop along the RPT to the RP. Upon receiving the prune message, the upstream node deletes the interface connected with this downstream node from the outgoing interface list and checks whether it has receivers for that IPv6 multicast group. If not, the router continues to forward the prune message to its upstream router.

Multicast source registration

The purpose of IPv6 multicast source registration is to inform the RP about the existence of the IPv6 multicast source.

Figure 1-6 IPv6 multicast source registration

As shown in Figure 1-6, the IPv6 multicast source registers with the RP as follows:

1) When the IPv6 multicast source S sends the first IPv6 multicast packet to IPv6 multicast group G, the DR directly connected with the multicast source, upon receiving the multicast packet, encapsulates the packet in a register message, and sends the message to the corresponding RP by unicast.

2) When the RP receives the register message, it extracts the multicast packet from the register message and forwards the multicast IPv6 multicast packet down the RPT, and sends an (S, G) join message hop by hop toward the IPv6 multicast source. Thus, the routers along the path from the RP to the IPv6 multicast source form an SPT branch. Each router on this branch generates an (S, G) entry in its forwarding table. The DR at the IPv6 multicast source side is the root, while the RP is the leaf, of the SPT.

3) The subsequent IPv6 multicast data from the IPv6 multicast source travels along the established SPT to the RP, and then the RP forwards the data along the RPT to the receivers. When the IPv6 multicast traffic arrives at the RP along the SPT, the RP sends a register-stop message to the source-side DR by unicast to stop the source registration process.

The RP is configured to initiate an SPT switchover as described in this section. Otherwise, the DR at the IPv6 multicast source side keeps encapsulating IPv6 multicast data in register messages and the registration process will not stop unless no outgoing interfaces exist in the (S, G) entry on the RP.

Switchover to SPT

In a IPv6 PIM-SM domain, a IPv6 multicast group corresponds to one RP and RPT. Before the SPT switchover takes place, the DR at the IPv6 multicast source side encapsulates all IPv6 multicast data destined to the multicast group in register messages and sends these messages to the RP. Upon receiving these register messages, the RP abstracts the IPv6 multicast data and sends the IPv6 multicast data down the RPT to the DRs at the receiver side. The RP acts as a transfer station for all IPv6 multicast packets. The whole process involves three issues as follows:

l The DR at the source side and the RP need to implement complicated encapsulation and decapsulation of IPv6 multicast packets.

l IPv6 Multicast packets are delivered along a path that is not necessarily the shortest one.

l When the IPv6 multicast traffic increases, a great burden is added to the RP, increasing the risk of failure.

To solve the issues, IPv6 PIM-SM allows an RP or the DR at the receiver side to initiate an SPT switchover process:

1) The RP initiates an SPT switchover process

Upon receiving the first IPv6 multicast packet, the RP sends an (S, G) join message hop by hop toward the IPv6 multicast source to establish an SPT between the DR at the source side and the RP. The subsequent IPv6 multicast data from the multicast source travel along the established SPT to the RP

For details about the SPT switchover initiated by the RP, refer to Multicast source registration.

2) The receiver-side DR initiates an SPT switchover process

Upon discovering that the traffic rate exceeds a configurable threshold, the receiver-side DR initiates an SPT switchover process, as follows:

l First, the receiver-side DR sends an (S, G) join message hop by hop toward the multicast source S. When the join message reaches the source-side DR, all the routers on the path have installed the (S, G) entry in their forwarding table, and thus an SPT branch is established.

l When subsequent IPv6 multicast packets arrive at the router at the junction of the RPT and SPT, the router drops those transmitted along the RPT and sends an RP-bit prune message containing the RP bit hop by hop to the RP. Upon receiving this prune message, the RP sends a prune message toward the IPv6 multicast source (suppose only one receiver exists), thus to implement SPT switchover.

IPv6 PIM-SM builds SPTs through SPT switchover more economically than IPv6 PIM-DM does through the “flood and prune” mechanism.

Assert

IPv6 PIM-SM uses the similar assert mechanism as IPv6 PIM-DM does. Refer to Assert.

SSM Model Implementation in IPv6 PIM

The source-specific multicast (SSM) model and the any-source multicast (ASM) model are two opposite models. Presently, the ASM model includes the IPv6 PIM-DM and IPv6 PIM-SM modes. The SSM model can be implemented by leveraging part of the IPv6 PIM-SM technique.

The SSM model provides a solution for source-specific multicast. It maintains the relationships between hosts and routers through MLDv2. IPv6 PIM-DM implements IPv6 multicast forwarding by building SPTs rooted at the IPv6 multicast source through the “flood and prune” mechanism. Although an SPT has the shortest path, it is built in a low efficiency. Therefore the IPv6 PIM-DM mod is not suitable for large- and medium-sized networks.

In actual application, part of the IPv6 PIM-SM technique is adopted to implement the SSM model. In the SSM model, receivers know exactly where an IPv6 multicast source is located by means of advertisements, consultancy, and so on. Therefore, no RP is needed, no RPT is required, and is no source registration process is needed for the purpose of discovering IPv6 multicast sources in other IPv6 PIM domains.

Compared with the ASM model, the SSM model only needs the support of MLDv2 and some subsets of IPv6 PIM-SM. The operation mechanism of the SSM model in an IPv6 PIM domain can be summarized as follows:

l Neighbor discovery

l DR election

l SPT building

Neighbor discovery

IPv6 PIM-SSM uses the same neighbor discovery mechanism as in IPv6 PIM-SM. Refer to Neighbor discovery.

DR election

IPv6 PIM-SSM uses the same DR election mechanism as in IPv6 PIM-SM. Refer to DR election.

SPT building

Whether to build an RPT for IPv6 PIM-SM or an SPT for IPv6 PIM-SSM depends on whether the IPv6 multicast group the receiver is to join falls in the IPv6 SSM group range (the IPv6 SSM group range reserved by IANA is FF3x::/32, where x represents any legal address scope).

Figure 1-7 Building an SPT in IPv6 PIM-SSM

As shown in Figure 1-7, Hosts B and C are IPv6 multicast information receivers. They send an MLDv2 report message to the respective DRs to announce that they are interested in the information of the specific IPv6 multicast source S and that sent to the IPv6 multicast group G.

The DR that has received the report first checks whether the IPv6 group address in this message falls in the IPv6 SSM group range:

l If so, the IPv6 PIM-SSM model is built: the DR sends a channel subscription message hop by hop toward the IPv6 multicast source S. An (S, G) entry is created on all routers on the path from the DR to the source. Thus, an SPT is built in the network, with the source S as its root and receivers as its leaves. This SPT is the transmission channel in IPv6 PIM-SSM.

l If not, the IPv6 PIM-SM process is followed: the DR needs to send a (*, G) join message to the RP, and an IPv6 multicast source registration process is needed.

In IPv6 PIM-SSM, the “channel” concept is used to refer to an IPv6 multicast group, and the “channel subscription” concept is used to refer to a join message.

Protocols and Standards

IPv6 PIM–related specifications are as follows:

l RFC 4601: Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification (Revised)

l RFC 3973: Protocol Independent Multicast-Dense Mode(PIM-DM):Protocol Specification(Revised)

l RFC 3956: Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address

l RFC 4607: Source-Specific Multicast for IP

l RFC 5059: Bootstrap Router (BSR) Mechanism for Protocol Independent Multicast (PIM)

l draft-ietf-ssm-overview-05: An Overview of Source-Specific Multicast (SSM)

Configuring IPv6 PIM-DM

IPv6 PIM-DM Configuration Task List

Complete these tasks to configure IPv6 PIM-DM:

Task	Remarks
Enabling IPv6 PIM-DM	Required
Enabling State-Refresh Capability	Optional
Configuring State Refresh Parameters	Optional
Configuring IPv6 PIM-DM Graft Retry Period	Optional
Configuring IPv6 PIM Common Features	Optional

Configuration Prerequisites

Before configuring IPv6 PIM-DM, complete the following task:

l Configure any IPv6 unicast routing protocol so that all devices in the domain are interoperable at the network layer.

Before configuring IPv6 PIM-DM, prepare the following data:

l The interval between state refresh messages

l Minimum time to wait before receiving a new refresh message

l Hop limit value of state-refresh messages

l Graft retry period

Enabling IPv6 PIM-DM

With IPv6 PIM-DM enabled, a router sends hello messages periodically to discover IPv6 PIM neighbors and processes messages from the IPv6 PIM neighbors. When deploying an IPv6 PIM-DM domain, you are recommended to enable IPv6 PIM-DM on all non-border interfaces of routers.

Follow these steps to enable IPv6 PIM-DM:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable IPv6 multicast routing	multicast ipv6 routing-enable	Required Disable by default
Enter interface view	interface interface-type interface-number	—
Enable IPv6 PIM-DM	pim ipv6 dm	Required Disabled by default

l All the interfaces of the same device must work in the same IPv6 PIM mode.

l IPv6 PIM-DM cannot be used for IPv6 multicast groups in the IPv6 SSM group range.

For details about the multicast ipv6 routing-enable command, see IPv6 Multicast Routing and Forwarding Commands in the IP Multicast Volume.

Enabling State-Refresh Capability

A multi-access subnet can have the state-refresh capability only if the state-refresh capability is enabled on all IPv6 PIM routers on the subnet.

Follow these steps to enable the state-refresh capability:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Enable the state-refresh capability	pim ipv6 state-refresh-capable	Optional Enabled by default

Configuring State Refresh Parameters

To avoid the resource-consuming reflooding of unwanted traffic caused by timeout of pruned interfaces, the router directly connected with the IPv6 multicast source periodically sends an (S, G) state-refresh message, which is forwarded hop by hop along the initial flooding path of the IPv6 PIM-DM domain, to refresh the prune timer state of all the routers on the path.

A router may receive multiple state-refresh messages within a short time, of which some may be duplicated messages. To keep a router from receiving such duplicated messages, you can configure the time the router must wait before receiving the next state-refresh message. If a new state-refresh message is received within the waiting time, the router will discard it; if this timer times out, the router will accept a new state-refresh message, refresh its own IPv6 PIM-DM state, and reset the waiting timer.

The hop limit value of a state-refresh message decrements by 1 whenever it passes a router before it is forwarded to the downstream node until the hop limit value comes down to 0. In a small network, a state-refresh message may cycle in the network. To effectively control the propagation scope of state-refresh messages, you need to configure an appropriate hop limit value based on the network size.

It is recommended to perform the following configurations on all routers in the IPv6 PIM domain.

Follow these steps to configure state-refresh parameters:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the interval between state-refresh messages	state-refresh-interval interval	Optional 60 seconds by default
Configure the time to wait before receiving a new state-refresh message	state-refresh-rate-limit interval	Optional 30 seconds by default
Configure the hop limit value of state-refresh messages	state-refresh-hoplimit hoplimit-value	Optional 255 by default

Configuring IPv6 PIM-DM Graft Retry Period

In IPv6 PIM-DM, graft is the only type of message that uses the acknowledgment mechanism. In an IPv6 PIM-DM domain, if a router does not receive a graft-ack message from the upstream router within the specified time after it sends a graft message, the router keeps sending new graft messages at a configurable interval, namely graft retry period, until it receives a graft-ack from the upstream router.

Follow these steps to configure IPv6 PIM-DM graft retry period:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configure graft retry period	pim ipv6 timer graft-retry interval	Optional 3 seconds by default

For the configuration of other timers in IPv6 PIM-DM, refer to Configuring IPv6 PIM Common Timers.

Configuring IPv6 PIM-SM

IPv6 PIM-SM Configuration Task List

Complete these tasks to configure IPv6 PIM-SM:

Task		Remarks
Enabling IPv6 PIM-SM		Required
Configuring an RP	Configuring a static RP	Optional
	Configuring a C-RP	Optional
	Enabling embedded RP	Optional
	Configuring C-RP timers globally	Optional
Configuring a BSR	Configuring a C-BSR	Optional
	Configuring an IPv6 PIM domain border	Optional
	Configuring C-BSR parameters globally	Optional
	Configuring C-BSR timers	Optional
Configuring IPv6 Multicast Source Registration		Optional
Disabling SPT Switchover		Optional
Configuring IPv6 PIM Common Features		Optional

Configuration Prerequisites

Before configuring IPv6 PIM-SM, complete the following task:

l Configure any IPv6 unicast routing protocol so that all devices in the domain are interoperable at the network layer.

Before configuring IPv6 PIM-SM, prepare the following data:

l The IP address of a static RP and an ACL rule defining the range of IPv6 multicast groups to be served by the static RP

l C-RP priority and an ACL rule defining the range of IPv6 multicast groups to be served by each C-RP

l A legal C-RP address range and an ACL rule defining the range of IPv6 multicast groups to be served

l C-RP-Adv interval

l C-RP timeout

l C-BSR priority

l Hash mask length

l An IPv6 ACL rule defining a legal BSR address range

l BS period

l BS timeout

l An IPv6 ACL rule for register message filtering

l Register suppression time

l Register probe time

l The IPv6 ACL rule and sequencing rule for disabling an SPT switchover

Enabling IPv6 PIM-SM

With IPv6 PIM-SM enabled, a router sends hello messages periodically to discover IPv6 PIM neighbors and processes messages from the IPv6 PIM neighbors. When deploying an IPv6 PIM-SM domain, you are recommended to enable IPv6 PIM-SM on all non-border interfaces of the routers.

Follow these steps to enable IPv6 PIM-SM:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable IPv6 multicast routing	multicast ipv6 routing-enable	Required Disable by default
Enter interface view	interface interface-type interface-number	—
Enable IPv6 PIM-SM	pim ipv6 sm	Required Disabled by default

All the interfaces of the same device must work in the same IPv6 PIM mode.

For details about the multicast ipv6 routing-enable command, see IPv6 Multicast Routing and Forwarding Commands in the IP Multicast Volume.

Configuring an RP

An RP can be manually configured or dynamically elected through the BSR mechanism. For a large IPv6 PIM network, static RP configuration is a tedious job. Generally, static RP configuration is just a backup means for the dynamic RP election mechanism to enhance the robustness and operation manageability of a multicast network.

Configuring a static RP

If there is only one dynamic RP in a network, manually configuring a static RP can avoid communication interruption due to single-point failures and avoid frequent message exchange between C-RPs and the BSR.

Perform the following configuration on all the routers in the IPv6 PIM-SM domain.

Follow these steps to configure a static RP:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure a static RP	static-rp ipv6-rp-address [ acl6-number ] [ preferred ]	Required No static RP by default

To enable a static RP to work normally, you must perform this configuration on all routers in the IPv6 PIM-SM domain and specify the same RP address.

Configuring a C-RP

In an IPv6 PIM-SM domain, you can configure routers that intend to become the RP as C-RPs. The BSR collects the C-RP information by receiving the C-RP-Adv messages from C-RPs or auto-RP announcements from other routers and organizes the information into an RP-Set, which is flooded throughout the entire network. Then, the other routers in the network calculate the mappings between specific group ranges and the corresponding RPs based on the RP-Set. We recommend that you configure C-RPs on backbone routers.

To guard against C-RP spoofing, you need to configure a legal C-RP address range and the range of IPv6 multicast groups to be served on the BSR. In addition, because every C-BSR has a chance to become the BSR, you need to configure the same filtering policy on all C-BSRs in the IPv6 PIM-SM domain.

Follow these steps to configure a C-RP:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure an interface to be a C-RP	c-rp ipv6-address [ group-policy acl6-number \| priority priority \| holdtime hold-interval \| advertisement-interval adv-interval ] *	Required No C-RPs are configured by default.
Configure a legal C-RP address range and the range of IPv6 multicast groups to be served	crp-policy acl6-number	Optional No restrictions by default

l When configuring a C-RP, ensure a relatively large bandwidth between this C-RP and the other devices in the IPv6 PIM-SM domain.

l An RP can serve multiple IPv6 multicast groups or all IPv6 multicast groups. Only one RP can forward IPv6 multicast traffic for an IPv6 multicast group at a moment.

Enabling embedded RP

With the Embedded RP feature enabled, the router can resolve the RP address directly from the IPv6 multicast group address of an IPv6 multicast packets. This RP can replace the statically configured RP or the RP dynamically calculated based on the BSR mechanism. Thus, the DR does not need to know the RP address beforehand.

Follow these steps to enable embedded RP:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Enable embedded RP	embedded-rp [ acl6-number ]	Optional By default, embedded RP is enabled for IPv6 multicast groups in the default embedded RP address scopes.

The default embedded RP address scopes are FF7x::/12 and FFFx::/12. Here “x” refers to any legal address scope. For details of the scope field, see Multicast Overview of the IP Multicast Volume.

Configuring C-RP timers globally

To enable the BSR to distribute the RP-Set information within the IPv6 PIM-SM domain, C-RPs must periodically send C-RP-Adv messages to the BSR. The BSR learns the RP-Set information from the received messages, and encapsulates its own IPv6 address together with the RP-Set information in its bootstrap messages. The BSR then floods the bootstrap messages to all IPv6 routers in the network.

Each C-RP encapsulates a timeout value in its C-RP-Adv messages. Upon receiving a C-RP-Adv message, the BSR obtains this timeout value and starts a C-RP timeout timer. If the BSR fails to hear a subsequent C-RP-Adv message from the C-RP when the timer times out, the BSR assumes the C-RP to have expired or become unreachable.

The C-RP timers need to be configured on C-RP routers.

Follow these steps to configure C-RP timers globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the C-RP-Adv interval	c-rp advertisement-interval interval	Optional 60 seconds by default
Configure C-RP timeout time	c-rp holdtime interval	Optional 150 seconds by default

For the configuration of other timers in IPv6 PIM-SM, refer to Configuring IPv6 PIM Common Timers.

Configuring a BSR

An IPv6 PIM-SM domain can have only one BSR, but must have at least one C-BSR. Any router can be configured as a C-BSR. Elected from C-BSRs, the BSR is responsible for collecting and advertising RP information in the IPv6 PIM-SM domain.

Configuring a C-BSR

C-BSRs should be configured on routers in the backbone network. When configuring a router as a C-BSR, make sure to specify the IPv6 address of an IPv6 PIM-SM enabled interface on the router. The BSR election process is summarized as follows:

l Initially, every C-BSR assumes itself to be the BSR of this IPv6 PIM-SM domain, and uses its interface IPv6 address as the BSR address to send bootstrap messages.

l When a C-BSR receives the bootstrap message of another C-BSR, it first compares its own priority with the other C-BSR’s priority carried in the message. The C-BSR with a higher priority wins. If there is a tie in the priority, the C-BSR with a higher IPv6 address wins. The loser uses the winner’s BSR address to replace its own BSR address and no longer assumes itself to be the BSR, while the winner keeps its own BSR address and continues assuming itself to be the BSR.

Configuring a legal range of BSR addresses enables filtering of bootstrap messages based on the address range, thus to prevent a maliciously configured host from masquerading as a BSR. The same configuration needs to be made on all routers in the IPv6 PIM-SM domain. The following are typical BSR spoofing cases and the corresponding preventive measures:

1) Some maliciously configured hosts can forge bootstrap messages to fool routers and change RP mappings. Such attacks often occur on border routers. Because a BSR is inside the network whereas hosts are outside the network, you can protect a BSR against attacks from external hosts by enabling the border routers to perform neighbor checks and RPF checks on bootstrap messages and discard unwanted messages.

2) When a router in the network is controlled by an attacker or when an illegal router is present in the network, the attacker can configure this router as a C-BSR and make it win BSR election to control the right of advertising RP information in the network. After being configured as a C-BSR, a router automatically floods the network with bootstrap messages. As a bootstrap message has a hop limit value of 1, the whole network will not be affected as long as the neighbor router discards these bootstrap messages. Therefore, with a legal BSR address range configured on all routers in the entire network, all these routers will discard bootstrap messages from out of the legal address range.

The above-mentioned preventive measures can partially protect the security of BSRs in a network. However, if a legal BSR is controlled by an attacker, the above-mentioned problem will also occur.

Follow these steps to complete basic BSR configuration:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure an interface as a C-BSR	c-bsr ipv6-address [ hash-length [ priority ] ]	Required No C-BSRs are configured by default.
Configure a legal BSR address range	bsr-policy acl6-number	Optional No restrictions by default

Since a large amount of information needs to be exchanged between a BSR and the other devices in the IPv6 PIM-SM domain, a relatively large bandwidth should be provided between the C-BSR and the other devices in the IPv6 PIM-SM domain.

Configuring an IPv6 PIM domain border

As the administrative core of an IPv6 PIM-SM domain, the BSR sends the collected RP-Set information in the form of bootstrap messages to all routers in the IPv6 PIM-SM domain.

An IPv6 PIM domain border is a bootstrap message boundary. Each BSR has its specific service scope. A number of IPv6 PIM domain border interfaces partition a network into different IPv6 PIM-SM domains. Bootstrap messages cannot cross a domain border in either direction.

Perform the following configuration on routers that can become an IPv6 PIM domain border.

Follow these steps to configure an IPv6 PIM border domain:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configuring an IPv6 PIM domain border	pim ipv6 bsr-boundary	Required No IPv6 PIM domain border is configured by default

Configuring C-BSR parameters globally

In each IPv6 PIM-SM domain, a unique BSR is elected from C-BSRs. The C-RPs in the IPv6 PIM-SM domain send advertisement messages to the BSR. The BSR summarizes the advertisement messages to form an RP-set and advertises it to all routers in the IPv6 PIM-SM domain. All the routers use the same Hash algorithm to get the RP address corresponding to specific IPv6 multicast groups.

Perform the following configuration on C-BSR routers.

Follow these steps to configure C-BSR parameters globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the Hash mask length	c-bsr hash-length hash-length	Optional 126 by default
Configure the C-BSR priority	c-bsr priority priority	Optional 0 by default

Configuring C-BSR timers

The BSR election winner multicasts its own IPv6 address and RP-Set information throughout the region that it serves through bootstrap messages. The BSR floods bootstrap messages throughout the network at the interval of BS (BSR state) period. Any C-BSR that receives a bootstrap message retains the RP-set for the length of BS timeout, during which no BSR election takes place. If the BSR state times out and no bootstrap message is received from the BSR, a new BSR election process is triggered among the C-BSRs.

Perform the following configuration on C-BSR routers.

Follow these steps to configure C-BSR timers:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the BS period	c-bsr interval interval	Optional For the default value, see the note below.
Configure the BS timeout	c-bsr holdtime interval	Optional For the default value, see the note below.

About the BS period:

l By default, the BS period is determined by this formula: BS period = (BS timeout – 10) / 2. The default BS timeout is 130 seconds, so the default BS period = (130 – 10) / 2 = 60 (seconds).

l If this parameter is manually configured, the system will use the configured value.

About the BS timeout:

l By default, the BS timeout value is determined by this formula: BS timeout = BS period × 2 + 10. The default BS period is 60 seconds, so the default BS timeout = 60 × 2 + 10 = 130 (seconds).

l If this parameter is manually configured, the system will use the configured value.

In configuration, make sure that the BS period is smaller than the BS timeout value.

Configuring IPv6 Multicast Source Registration

Within an IPv6 PIM-SM domain, the source-side DR sends register messages to the RP, and these register messages have different IPv6 multicast source or IPv6 multicast group addresses. You can configure a filtering rule to filter register messages so that the RP can serve specific IPv6 multicast groups. If an (S, G) entry is denied by the filtering rule, or the action for this entry is not defined in the filtering rule, the RP will send a register-stop message to the DR to stop the registration process for the IPv6 multicast data.

In view of information integrity of register messages in the transmission process, you can configure the device to calculate the checksum based on the entire register messages. However, to reduce the workload of encapsulating data in register messages and for the sake of interoperability, this method of checksum calculation is not recommended.

When receivers stop receiving data addressed to a certain IPv6 multicast group through the RP (that is, the RP stops serving the receivers of that IPv6 multicast group), or when the RP formally starts receiving IPv6 multicast data from the IPv6 multicast source, the RP sends a register-stop message to the source-side DR. Upon receiving this message, the DR stops sending register messages encapsulated with IPv6 multicast data and starts a register-stop timer. When the register-stop timer expires, the DR sends a null register message (a register message without encapsulated multicast data) to the RP. If the DR receives a register-stop message during the register probe time, it will reset its register-stop timer; otherwise, the DR starts sending register messages with encapsulated data again when the register-stop timer expires.

The Register-Stop Timer is set to a random value chosen uniformly from the interval (0.5 times register_suppression_time, 1.5 times register_suppression_time) minus register_probe_time.

Configure a filtering rule for register messages on all C-RP routers and configure them to calculate the checksum based on the entire register messages. Configure the register suppression time and the register probe time on all routers that may become source-side DRs.

Follow these steps to configure register-related parameters:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure a filtering rule for register messages	register-policy acl6-number	Optional No register filtering rule by default
Configure the device to calculate the checksum based on the entire register messages	register-whole-checksum	Optional Based on the header of register messages by default
Configure the register suppression time	register-suppression-timeout interval	Optional 60 seconds by default
Configure the register probe time	probe-interval interval	Optional 5 seconds by default

Disabling SPT Switchover

If an S7500E series routing switch acts as an RP or the receiver-side DR, it initiates an SPT switchover process (by default) upon receiving the first IPv6 multicast packet along the RPT. You can disable the switchover from RPT to SPT

Follow these steps to disable SPT switchover:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter PIM view	pim	—
Apply the ACL for initiating an SPT switchover	spt-switch-threshold infinity [ group-policy acl6-number [ order order-value] ]	Optional By default, the last-hop switch initiates an RPT-to-SPT switchover process when it receives the first IPv6 multicast packet.

For an S7500E series Ethernet switch, once an IPv6 multicast forwarding entry is created, subsequent IPv6 multicast data will not be encapsulated in register messages before being forwarded even if a register outgoing interface is available. Therefore, to avoid forwarding failure, do not use spt-switch-threshold infinity command on a switch that may become an RP (namely, a static RP or a C-RP).

Configuring IPv6 PIM-SSM

The IPv6 PIM-SSM model needs the support of MLDv2. Therefore, be sure to enable MLDv2 on IPv6 PIM routers with receivers attached to them.

IPv6 PIM-SSM Configuration Task List

Complete these tasks to configure IPv6 PIM-SSM:

Task	Remarks
Enabling IPv6 PIM-SM	Required
Configuring the IPv6 SSM Group Range	Optional
Configuring IPv6 PIM Common Features	Optional

Configuration Prerequisites

Before configuring IPv6 PIM-SSM, complete the following task:

l Configure any IPv6 unicast routing protocol so that all devices in the domain are interoperable at the network layer.

Before configuring IPv6 PIM-SSM, prepare the following data:

l The IPv6 SSM group range

Enabling IPv6 PIM-SM

The SSM model is implemented based on some subsets of IPv6 PIM-SM. Therefore, a router is IPv6 PIM-SSM capable after you enable IPv6 PIM-SM on it.

When deploying an IPv6 PIM-SM domain, you are recommended to enable IPv6 PIM-SM on all non-border interfaces of routers.

Follow these steps to enable IPv6 PIM-SSM:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable IPv6 multicast routing	multicast ipv6 routing-enable	Required Disable by default
Enter interface view	interface interface-type interface-number	—
Enable IPv6 PIM-SM	pim ipv6 sm	Required Disabled by default

All the interfaces of the same device must work in the same IPv6 PIM mode.

For details about the multicast ipv6 routing-enable command, see IPv6 Multicast Routing and Forwarding Commands in the IP Multicast Volume.

Configuring the IPv6 SSM Group Range

As for whether the information from an IPv6 multicast source is delivered to the receivers based on the IPv6 PIM-SSM model or the IPv6 PIM-SM model, this depends on whether the group address in the (S, G) channel subscribed by the receivers falls in the IPv6 SSM group range. All IPv6 PIM-SM-enabled interfaces assume that IPv6 multicast groups within this address range are using the IPv6 SSM model.

Perform the following configuration on all routers in the IPv6 PIM-SM domain.

Follow these steps to configure the IPv6 SSM group range:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the IPv6 SSM group range	ssm-policy acl6-number	Optional FF3x::/32 by default, here “x” refers to any legal group scope.

l Make sure that the same IPv6 SSM group range is configured on all routers in the entire domain. Otherwise, IPv6 multicast data cannot be delivered through the IPv6 SSM model.

l When a member of an IPv6 multicast group in the IPv6 SSM group range sends an MLDv1 report message, the device does not trigger a (*, G) join.

Configuring IPv6 PIM Common Features

For the functions or parameters that can be configured in both IPv6 PIM view and interface view described in this section:

l Configurations performed in IPv6 PIM view are effective to all interfaces, while configurations performed in interface view are effective to the current interface only.

l If the same function or parameter is configured in both IPv6 PIM view and interface view, the configuration made in interface view has preference over the configuration made in PIM view, regardless of the configuration sequence.

IPv6 PIM Common Feature Configuration Task List

Complete these tasks to configure IPv6 PIM common features:

Task	Remarks
Configuring an IPv6 Multicast Data Filter	Optional
Configuring IPv6 PIM Hello Options	Optional
Configuring IPv6 PIM Common Timers	Optional
Configuring Join/Prune Message Sizes	Optional

Configuration Prerequisites

Before configuring IPv6 PIM common features, complete the following tasks:

l Configure any IPv6 unicast routing protocol so that all devices in the domain are interoperable at the network layer.

l Configure IPv6 PIM-DM (or IPv6 PIM-SM or IPv6 PIM-SSM).

Before configuring IPv6 PIM common features, prepare the following data:

l An IPv6 ACL rule for filtering IPv6 multicast data

l Priority for DR election (global value/interface level value)

l IPv6 PIM neighbor timeout time (global value/interface value)

l Prune delay (global value/interface level value)

l Prune override interval (global value/interface level value)

l Hello interval (global value/interface level value)

l Maximum delay between hello message (interface level value)

l Assert timeout time (global value/interface value)

l Join/prune interval (global value/interface level value)

l Join/prune timeout (global value/interface value)

l IPv6 multicast source lifetime

l Maximum size of join/prune messages

l Maximum number of (S, G) entries in a join/prune message

Configuring an IPv6 Multicast Data Filter

No matter in an IPv6 PIM-DM domain or an IPv6 PIM-SM domain, routers can check passing-by IPv6 multicast data based on the configured filtering rules and determine whether to continue forwarding the IPv6 multicast data. In other words, IPv6 PIM routers can act as IPv6 multicast data filters. These filters can help implement traffic control on one hand, and control the information available to downstream receivers to enhance data security on the other hand.

Follow these steps to configure an IPv6 multicast data filter:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure an IPv6 multicast group filter	source-policy acl6-number	Required No IPv6 multicast data filter by default

l Generally, a smaller distance from the filter to the IPv6 multicast source results in a more remarkable filtering effect.

l This filter works not only on independent IPv6 multicast data but also on IPv6 multicast data encapsulated in register messages.

Configuring IPv6 PIM Hello Options

No matter in an IPv6 PIM-DM domain or an IPv6 PIM-SM domain, the hello messages sent among routers contain many configurable options, including:

l DR_Priority (for IPv6 PIM-SM only): priority for DR election. The higher the priority is, the easier it is for the router to win DR election. You can configure this parameter on all the routers in a multi-access network directly connected to IPv6 multicast sources or receivers.

l Holdtime: the timeout time of IPv6 PIM neighbor reachability state. When this timer times out, if the router has received no hello message from an IPv6 PIM neighbor, it assumes that this neighbor has expired or become unreachable.

l LAN_Prune_Delay: the delay of prune messages on a multi-access network. This option consists of Lan-delay (namely, prune delay), Override-interval, and neighbor tracking flag. If the LAN-delay or override-interval values of different IPv6 PIM routers on a multi-access subnet are different, the largest value will take effect. If you want to enable neighbor tracking, the neighbor tracking feature should be enabled on all IPv6 PIM routers on a multi-access subnet.

The LAN-delay setting will cause the upstream routers to delay processing received prune messages. If the LAN-delay setting is too small, it may cause the upstream router to stop forwarding IPv6 multicast packets before a downstream router sends a prune override message. Therefore, be cautious when configuring this parameter.

The override-interval sets the length of time a downstream router is allowed to wait before sending a prune override message. When a router receives a prune message from a downstream router, it does not perform the prune action immediately; instead, it maintains the current forwarding state for a period of LAN-delay plus override-interval. If the downstream router needs to continue receiving IPv6 multicast data, it must send a prune override message within the prune override interval; otherwise, the upstream route will perform the prune action when the period of LAN-delay plus override-interval time out.

A hello message sent from an IPv6 PIM router contains a generation ID option. The generation ID is a random value for the interface on which the hello message is sent. Normally, the generation ID of an IPv6 PIM router does not change unless the status of the router changes (for example, when IPv6 PIM is just enabled on the interface or the device is restarted). When the router starts or restarts sending hello messages, it generates a new generation ID. If an IPv6 PIM router finds that the generation ID in a hello message from the upstream router has changed, it assumes that the status of the upstream neighbor is lost or the upstream neighbor has changed. In this case, it triggers a join message for state update.

If you disable join suppression (namely, enable neighbor tracking), the join suppression feature should be disabled on all IPv6 PIM routers on a multi-access subnet; otherwise, the upstream router will fail to explicitly track which downstream routers are joined to it.

Configuring hello options globally

Follow these steps to configure hello options globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the priority for DR election	hello-option dr-priority priority	Optional 1 by default
Configure IPv6 PIM neighbor timeout time	hello-option holdtime interval	Optional 105 seconds by default
Configure the prune delay time (LAN-delay)	hello-option lan-delay interval	Optional 500 milliseconds by default
Configure the prune override interval	hello-option override-interval interval	Optional 2,500 milliseconds by default
Disable join suppression	hello-option neighbor-tracking	Required Enabled by default

Configuring hello options on an interface

Follow these steps to configure hello options on an interface:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configure the priority for DR election	pim ipv6 hello-option dr-priority priority	Optional 1 by default
Configure IPv6 PIM neighbor timeout time	pim ipv6 hello-option holdtime interval	Optional 105 seconds by default
Configure the prune delay time (LAN-delay)	pim ipv6 hello-option lan-delay interval	Optional 500 milliseconds by default
Configure the prune override interval	pim ipv6 hello-option override-interval interval	Optional 2,500 milliseconds by default
Disable join suppression	pim ipv6 hello-option neighbor-tracking	Required Enabled by default
Configure the interface to reject hello messages without a generation ID	pim ipv6 require-genid	Required By default, hello messages without Generation_ID are accepted.

Configuring IPv6 PIM Common Timers

IPv6 PIM routers discover IPv6 PIM neighbors and maintain IPv6 PIM neighboring relationships with other routers by periodically sending out hello messages.

Upon receiving a hello message, an IPv6 PIM router waits a random period, which is smaller than the maximum delay between hello messages, before sending out a hello message. This avoids collisions that occur when multiple IPv6 PIM routers send hello messages simultaneously.

An IPv6 PIM router periodically sends join/prune messages to its upstream for state update. A join/prune message contains the join/prune timeout time. The upstream router sets a join/prune timeout timer for each pruned downstream interface.

Any router that has lost assert election will prune its downstream interface and maintain the assert state for a period of time. When the assert state times out, the assert loser will resume IPv6 multicast forwarding.

When a router fails to receive subsequent IPv6 multicast data from the IPv6 multicast source S, the router does not immediately delete the corresponding (S, G) entry; instead, it maintains the (S, G) entry for a period of time, namely the IPv6 multicast source lifetime, before deleting the (S, G) entry.

Configuring IPv6 PIM common timers globally

Follow these steps to configure IPv6 PIM common timers globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the hello interval	timer hello interval	Optional 30 seconds by default
Configure the join/prune interval	timer join-prune interval	Optional 60 seconds by default
Configure the join/prune timeout time	holdtime join-prune interval	Optional 210 seconds by default
Configure assert timeout time	holdtime assert interval	Optional 180 seconds by default
Configure the IPv6 multicast source lifetime	source-lifetime interval	Optional 210 seconds by default

Configuring IPv6 PIM common timers on an interface

Follow these steps to configure IPv6 PIM common timers on an interface:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter interface view	interface interface-type interface-number	—
Configure the hello interval	pim ipv6 timer hello interval	Optional 30 seconds by default
Configure the maximum delay between hello messages	pim ipv6 triggered-hello-delay interval	Optional 5 seconds by default
Configure the join/prune interval	pim ipv6 timer join-prune interval	Optional 60 seconds by default
Configure the join/prune timeout time	pim ipv6 holdtime join-prune interval	Optional 210 seconds by default
Configure assert timeout time	pim ipv6 holdtime assert interval	Optional 180 seconds by default

If there are no special networking requirements, we recommend that you use the default settings.

Configuring Join/Prune Message Sizes

A larger join/prune message size will result in loss of a larger amount of information when a message is lost; with a reduced join/message size, the loss of a single message will bring relatively minor impact.

By controlling the maximum number of (S, G) entries in a join/prune message, you can effectively reduce the number of (S, G) entries sent per unit of time.

Follow these steps to configure join/prune message sizes:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IPv6 PIM view	pim ipv6	—
Configure the maximum size of a join/prune message	jp-pkt-size packet-size	Optional 8,100 bytes by default
Configure the maximum number of (S, G) entries in a join/prune message	jp-queue-size queue-size	Optional 1,020 by default

Displaying and Maintaining IPv6 PIM

To do...	Use the command...	Remarks
View the BSR information in the IPv6 PIM-SM domain and locally configured C-RP information in effect	display pim ipv6 bsr-info	Available in any view
View the information of IPv6 unicast routes used by IPv6 PIM	display pim ipv6 claimed-route [ ipv6-source-address ]	Available in any view
View the number of IPv6 PIM control messages	display pim ipv6 control-message counters [ message-type { probe \| register \| register-stop } \| [ interface interface-type interface-number \| message-type { assert \| bsr \| crp \| graft \| graft-ack \| hello \| join-prune \| state-refresh } ] * ]	Available in any view
View the information about unacknowledged graft messages	display pim ipv6 grafts	Available in any view
View the IPv6 PIM information on an interface or all interfaces	display pim ipv6 interface [ interface-type interface-number ] [ verbose ]	Available in any view
View the information of join/prune messages to send	display pim ipv6 join-prune mode { sm [ flags flag-value ] \| ssm } [ interface interface-type interface-number \| neighbor ipv6-neighbor-address ] * [ verbose ]	Available in any view
View IPv6 PIM neighboring information	display pim ipv6 neighbor [ interface interface-type interface-number \| ipv6-neighbor-address \| verbose ] *	Available in any view
View the content of the IPv6 PIM routing table	display pim ipv6 routing-table [ ipv6-group-address [ prefix-length ] \| ipv6-source-address [ prefix-length ] \| incoming-interface [ interface-type interface-number \| register ] \| outgoing-interface { include \| exclude \| match } { interface-type interface-number \| register } \| mode mode-type \| flags flag-value \| fsm ] *	Available in any view
View the RP information	display pim ipv6 rp-info [ ipv6-group-address ]	Available in any view
Reset IPv6 PIM control message counters	reset pim ipv6 control-message counters [ interface interface-type interface-number ]	Available in user view

IPv6 PIM Configuration Examples

IPv6 PIM-DM Configuration Example

Network requirements

l Receivers receive VOD information through multicast. The receiver groups of different organizations form stub networks, and one or more receiver hosts exist in each stub network. The entire IPv6 PIM domain operates in the dense mode.

l Host A and Host C are multicast receivers in two stub networks N1 and N2.

l Switch D connects to the network that comprises the multicast source (Source) through VLAN-interface 300.

l Switch A connects to N1 through VLAN-interface 100, and to Switch D through VLAN-interface 103.

l Switch B and Switch C connect to N2 through their respective VLAN-interface 200, and to Switch D through VLAN-interface 101 and VLAN-interface 102 respectively.

l MLDv1 is to run between Switch A and N1, and between Switch B/Switch C and N2.

Network diagram

Figure 1-8 Network diagram for IPv6 PIM-DM configuration

Device	Interface	IP address	Device	Interface	IP address
Switch A	Vlan-int100	1001::1/64	Switch D	Vlan-int300	4001::1/64
	Vlan-int103	1002::1/64		Vlan-int103	1002::2/64
Switch B	Vlan-int200	2001::1/64		Vlan-int101	2002::2/64
	Vlan-int101	2002::1/64		Vlan-int102	3001::2/64
Switch C	Vlan-int200	2001::2/64
	Vlan-int102	3001::1/64

Configuration procedure

1) Enable IPv6 forwarding and configure IPv6 addresses and IPv6 unicast routing

Enable IPv6 forwarding on each switch and configure the IPv6 address and prefix length for each interface as per Figure 1-8. Detailed configuration steps are omitted here.

Configure OSPFv3 for interoperation among the switches in the PIM-DM domain. Ensure the network-layer interoperation in the PIM-DM domain and enable dynamic update of routing information among the switches through an IPv6 unicast routing protocol. Detailed configuration steps are omitted here.

2) Enable IPv6 multicast routing, and enable IPv6 PIM-DM and MLD

# Enable IPv6 multicast routing on Switch A, enable IPv6 PIM-DM on each interface, and enable MLD on VLAN-interface 100, which connects Switch A to N1.

<SwitchA> system-view

[SwitchA] multicast ipv6 routing-enable

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] mld enable

[SwitchA-Vlan-interface100] pim ipv6 dm

[SwitchA-Vlan-interface100] quit

[SwitchA] interface vlan-interface 103

[SwitchA-Vlan-interface103] pim ipv6 dm

[SwitchA-Vlan-interface103] quit

The configuration on Switch B and Switch C is similar to that on Switch A.

# Enable IPv6 multicast routing on Switch D, and enable IPv6 PIM-DM on each interface.

<SwitchD> system-view

[SwitchD] multicast ipv6 routing-enable

[SwitchD] interface vlan-interface 300

[SwitchD-Vlan-interface300] pim ipv6 dm

[SwitchD-Vlan-interface300] quit

[SwitchD] interface vlan-interface 103

[SwitchD-Vlan-interface103] pim ipv6 dm

[SwitchD-Vlan-interface103] quit

[SwitchD] interface vlan-interface 101

[SwitchD-Vlan-interface101] pim ipv6 dm

[SwitchD-Vlan-interface101] quit

[SwitchD] interface vlan-interface 102

[SwitchD-Vlan-interface102] pim ipv6 dm

[SwitchD-Vlan-interface102] quit

3) Verify the configuration

Use the display pim ipv6 interface command to view the IPv6 PIM configuration and running status on each interface. For example:

# View the IPv6 PIM configuration information on Switch D.

[SwitchD] display pim ipv6 interface

Interface NbrCnt HelloInt DR-Pri DR-Address

Vlan300 0 30 1 4001::1

(local)

Vlan103 0 30 1 1002::2

(local)

Vlan101 1 30 1 2002::2

(local)

Vlan102 1 30 1 3001::2

(local)

Use the display pim ipv6 neighbor command to view the IPv6 PIM neighboring relationships among the switches. For example:

# View the IPv6 PIM neighboring relationships on Switch D.

[SwitchD] display pim ipv6 neighbor

Total Number of Neighbors = 3

Neighbor Interface Uptime Expires Dr-Priority

1002::1 Vlan103 00:04:00 00:01:29 1

2002::1 Vlan101 00:04:16 00:01:29 3

3001::1 Vlan102 00:03:54 00:01:17 5

Assume that Host A needs to receive the information addressed to IPv6 multicast group G (FF0E::101). After IPv6 multicast source S (4001::100/64) sends IPv6 multicast packets to the IPv6 multicast group G, an SPT is established through traffic flooding. Switches on the SPT path (Switch A and Switch D) have their (S, G) entries. Host A sends an MLD report to Switch A to join IPv6 multicast group G, and a (*, G) entry is generated on Switch A. You can use the display pim IPv6 routing-table command to view the IPv6 PIM routing table information on each switch. For example:

# View the IPv6 PIM multicast routing table information on Switch A.

[SwitchA] display pim ipv6 routing-table

Total 1 (*, G) entry; 1 (S, G) entry

(*, FF0E::101)

Protocol: pim-dm, Flag: WC

UpTime: 00:01:24

Upstream interface: NULL

Upstream neighbor: NULL

RPF prime neighbor: NULL

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface100

Protocol: mld, UpTime: 00:01:20, Expires: never

(4001::100, FF0E::101)

Protocol: pim-dm, Flag: ACT

UpTime: 00:01:20

Upstream interface: Vlan-interface103

Upstream neighbor: 1002::2

RPF prime neighbor: 1002::2

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface100

Protocol: pim-dm, UpTime: 00:01:20, Expires: never

The information on Switch B and Switch C is similar to that on Switch A.

# View the IPv6 PIM multicast routing table information on Switch D.

[SwitchD] display pim ipv6 routing-table

Total 0 (*, G) entry; 1 (S, G) entry

(4001::100, FF0E::101)

Protocol: pim-dm, Flag: LOC ACT

UpTime: 00:02:19

Upstream interface: Vlan-interface300

Upstream neighbor: NULL

RPF prime neighbor: NULL

Downstream interface(s) information:

Total number of downstreams: 3

1: Vlan-interface103

Protocol: pim-dm, UpTime: 00:02:19, Expires: never

2: Vlan-interface101

Protocol: pim-dm, UpTime: 00:02:19, Expires: never

3: Vlan-interface102

Protocol: pim-dm, UpTime: 00:02:19, Expires: never

IPv6 PIM-SM Configuration Example

Network requirements

l Host A and Host C are IPv6 multicast receivers in two stub networks N1 and N2.

l Switch D connects to the network that comprises the IPv6 multicast source (Source) through VLAN-interface 300.

l Switch A connects to N1 through VLAN-interface 100, and to Switch D and Switch E through VLAN-interface 101 and VLAN-interface 102 respectively.

l Switch B and Switch C connect to N2 through their respective VLAN-interface 200, and to Switch E through VLAN-interface 103 and VLAN-interface 104 respectively.

l Vlan-interface 105 on Switch D and Vlan-interface 102 on Switch E act as C-BSRs and C-RPs; the C-BSR on Switch E has a higher priority; the IPv6 multicast group range served by the C-RP is FF0E::101/64; modify the hash mask length to map a certain number of consecutive IPv6 group addresses within the range to the two C-RPs.

l MLDv1 is to run between Switch A and N1, and between Switch B/Switch C and N2.

Network diagram

Figure 1-9 Network diagram for IPv6 PIM-SM configuration

Device	Interface	IP address	Device	Interface	IP address
Switch A	Vlan-int100	1001::1/64	Switch D	Vlan-int300	4001::1/64
	Vlan-int101	1002::1/64		Vlan-int101	1002::2/64
	Vlan-int102	1003::1/64		Vlan-int105	4002::1/64
Switch B	Vlan-int200	2001::1/64	Switch E	Vlan-int104	3001::2/64
	Vlan-int103	2002::1/64		Vlan-int103	2002::2/64
Switch C	Vlan-int200	2001::2/64		Vlan-int102	1003::2/64
	Vlan-int104	3001::1/64		Vlan-int105	4002::2/64

Configuration procedure

1) Enable IPv6 forwarding and configure IPv6 addresses and IPv6 unicast routing

Enable IPv6 forwarding on each switch and configure the IPv6 address and prefix length for each interface as per Figure 1-9. Detailed configuration steps are omitted here.

Configure OSPFv3 for interoperation among the switches in the IPv6 PIM-SM domain. Ensure the network-layer interoperation in the IPv6 PIM-DM domain and enable dynamic update of routing information among the switches through an IPv6 unicast routing protocol. Detailed configuration steps are omitted here.

2) Enable IPv6 multicast routing, and enable IPv6 PIM-SM and MLD

# Enable IPv6 multicast routing on Switch A, enable IPv6 PIM-SM on each interface, and enable MLD on VLAN-interface 100, which connects Switch A to N1.

<SwitchA> system-view

[SwitchA] multicast ipv6 routing-enable

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] mld enable

[SwitchA-Vlan-interface100] pim ipv6 sm

[SwitchA-Vlan-interface100] quit

[SwitchA] interface vlan-interface 101

[SwitchA-Vlan-interface101] pim ipv6 sm

[SwitchA-Vlan-interface101] quit

[SwitchA] interface vlan-interface 102

[SwitchA-Vlan-interface102] pim ipv6 sm

[SwitchA-Vlan-interface102] quit

The configuration on Switch B and Switch C is similar to that on Switch A. The configuration on Switch D and Switch E is also similar to that on Switch A except that it is not necessary to enable MLD on the corresponding interfaces on these two switches.

3) Configure a C-BSR and a C-RP

# On Switch D, configure the service scope of RP advertisements, specify a C-BSR and a C-RP, and set the hash mask length to 128 and the priority of the C-BSR to 10.

<SwitchD> system-view

[SwitchD] acl ipv6 number 2005

[SwitchD-acl6-basic-2005] rule permit source ff0e::101 64

[SwitchD-acl6-basic-2005] quit

[SwitchD] pim ipv6

[SwitchD-pim6] c-bsr 4002::1 128 10

[SwitchD-pim6] c-rp 4002::1 group-policy 2005

[SwitchD-pim6] quit

# On Switch E, configure the service scope of RP advertisements, specify a C-BSR and a C-RP, and set the hash mask length to 128 and the priority of the C-BSR to 20.

<SwitchE> system-view

[SwitchE] acl ipv6 number 2005

[SwitchE-acl6-basic-2005] rule permit source ff0e::101 64

[SwitchE-acl6-basic-2005] quit

[SwitchE] pim ipv6

[SwitchE-pim6] c-bsr 1003::2 128 20

[SwitchE-pim6] c-rp 1003::2 group-policy 2005

[SwitchE-pim6] quit

4) Verify the configuration

Use the display pim ipv6 interface command to view the IPv6 PIM configuration and running status on each interface. For example:

# View the IPv6 PIM information on all interfaces of Switch A.

[SwitchA] display pim ipv6 interface

Interface NbrCnt HelloInt DR-Pri DR-Address

Vlan100 0 30 1 1001::1

(local)

Vlan101 1 30 1 1002::2

Vlan102 1 30 1 1003::2

To view the BSR election information and the locally configured C-RP information in effect on a switch, use the display pim ipv6 bsr-info command. For example:

# View the BSR information and the locally configured C-RP information in effect on Switch A.

[SwitchA] display pim ipv6 bsr-info

Elected BSR Address: 1003::2

Priority: 20

Hash mask length: 128

State: Accept Preferred

Uptime: 00:04:22

Expires: 00:01:46

# View the BSR information and the locally configured C-RP information in effect on Switch D.

[SwitchD] display pim ipv6 bsr-info

Elected BSR Address: 1003::2

Priority: 20

Hash mask length: 128

State: Elected

Uptime: 00:05:26

Expires: 00:01:45

Candidate BSR Address: 4002::1

Priority: 10

Hash mask length: 128

State: Candidate

Candidate RP: 4002::1(Vlan-interface105)

Priority: 0

HoldTime: 130

Advertisement Interval: 60

Next advertisement scheduled at: 00:00:48

# View the BSR information and the locally configured C-RP information in effect on Switch E.

[SwitchE] display pim ipv6 bsr-info

Elected BSR Address: 1003::2

Priority: 20

Hash mask length: 128

State: Elected

Uptime: 00:01:10

Next BSR message scheduled at: 00:01:48

Candidate BSR Address: 1003::2

Priority: 20

Hash mask length: 128

State: Elected

Candidate RP: 1003::2(Vlan-interface102)

Priority: 0

HoldTime: 130

Advertisement Interval: 60

Next advertisement scheduled at: 00:00:48

To view the RP information discovered on a switch, use the display pim ipv6 rp-info command. For example:

# View the RP information on Switch A.

[SwitchA] display pim ipv6 rp-info

PIM-SM BSR RP information:

prefix/prefix length: FF0E::101/64

RP: 4002::1

Priority: 0

HoldTime: 130

Uptime: 00:05:19

Expires: 00:02:11

RP: 1003::2

Priority: 0

HoldTime: 130

Uptime: 00:05:19

Expires: 00:02:11

Assume that Host A needs to receive information addressed to the IPv6 multicast group G (FF0E::100). The RP corresponding to the multicast group G is Switch E as a result of hash calculation, so an RPT will be built between Switch A and Switch E. When the IPv6 multicast source S (4001::100/64) registers with the RP, an SPT will be built between Switch D and Switch E. Upon receiving IPv6 multicast data, Switch A immediately switches from the RPT to the SPT. Switches on the RPT path (Switch A and Switch E) have a (*, G) entry, while switches on the SPT path (Switch A and Switch D) have an (S, G) entry. You can use the display pim ipv6 routing-table command to view the PIM routing table information on the switches. For example:

# View the IPv6 PIM multicast routing table information on Switch A.

[SwitchA] display pim ipv6 routing-table

Total 1 (*, G) entry; 1 (S, G) entry

(*, FF0E::100)

RP: 1003::2

Protocol: pim-sm, Flag: WC

UpTime: 00:03:45

Upstream interface: Vlan-interface102

Upstream neighbor: 1002::2

RPF prime neighbor: 1002::2

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface100

Protocol: mld, UpTime: 00:02:15, Expires: 00:03:06

(4001::100, FF0E::100)

RP: 1003::2

Protocol: pim-sm, Flag: SPT ACT

UpTime: 00:02:15

Upstream interface: Vlan-interface101

Upstream neighbor: 1003::2

RPF prime neighbor: 1003::2

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface100

Protocol: pim-sm, UpTime: 00:02:15, Expires: 00:03:06

The information on Switch B and Switch C is similar to that on Switch A.

# View the IPv6 PIM multicast routing table information on Switch D.

[SwitchD] display pim ipv6 routing-table

Total 0 (*, G) entry; 1 (S, G) entry

(4001::100, FF0E::100)

RP: 1003::2

Protocol: pim-sm, Flag: SPT LOC ACT

UpTime: 00:14:44

Upstream interface: Vlan-interface300

Upstream neighbor: NULL

RPF prime neighbor: NULL

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface105

Protocol: mld, UpTime: 00:14:44, Expires: 00:02:26

# View the IPv6 PIM multicast routing table information on Switch E.

[SwitchE] display pim ipv6 routing-table

Total 1 (*, G) entry; 0 (S, G) entry

(*, FF0E::100)

RP: 1003::2 (local)

Protocol: pim-sm, Flag: WC

UpTime: 00:16:56

Upstream interface: Register

Upstream neighbor: 4002::1

RPF prime neighbor: 4002::1

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface102

Protocol: pim-sm, UpTime: 00:16:56, Expires: 00:02:34

IPv6 PIM-SSM Configuration Example

Network requirements

l Host A and Host C are IPv6 multicast receivers in two stub networks N1 and N2.

l Switch D connects to the network that comprises the IPv6 multicast source (Source) through VLAN-interface 300.

l Switch A connects to N1 through VLAN-interface 100, and to Switch D and Switch E through VLAN-interface 101 and VLAN-interface 102 respectively.

l Switch B and Switch C connect to N2 through their respective VLAN-interface 200, and to Switch E through VLAN-interface 103 and VLAN-interface 104 respectively.

l Switch E connects to Switch A, Switch B, Switch C and Switch D.

l The SSM group range is FF3E::/64.

l MLDv2 is to run between Switch A and N1, and between Switch B/Switch C and N2.

Network diagram

Figure 1-10 Network diagram for IPv6 PIM-SSM configuration

Device	Interface	IP address	Device	Interface	IP address
Switch A	Vlan-int100	1001::1/64	Switch D	Vlan-int300	4001::1/64
	Vlan-int101	1002::1/64		Vlan-int101	1002::2/64
	Vlan-int102	1003::1/64		Vlan-int105	4002::1/64
Switch B	Vlan-int200	2001::1/64	Switch E	Vlan-int104	3001::2/64
	Vlan-int103	2002::1/64		Vlan-int103	2002::2/64
Switch C	Vlan-int200	2001::2/64		Vlan-int102	1003::2/64
	Vlan-int104	3001::1/64		Vlan-int105	4002::2/64

Configuration procedure

1) Enable IPv6 forwarding and configure IPv6 addresses and IPv6 unicast routing

Enable IPv6 forwarding on each switch and configure the IPv6 address and prefix length for each interface as per Figure 1-10. Detailed configuration steps are omitted here.

Configure OSPFv3 for interoperation among the switches in the IPv6 PIM-SM domain. Ensure the network-layer interoperation in the IPv6 PIM-SM domain and enable dynamic update of routing information among the switches through an IPv6 unicast routing protocol. Detailed configuration steps are omitted here.

2) Enable IPv6 multicast routing, and enable IPv6 PIM-SM and MLD

# Enable IPv6 multicast routing on Switch A, enable IPv6 PIM-SM on each interface, and run MLDv2 on VLAN-interface 100, which connects Switch A to N1.

<SwitchA> system-view

[SwitchA] multicast ipv6 routing-enable

[SwitchA] interface vlan-interface 100

[SwitchA-Vlan-interface100] mld enable

[SwitchA-Vlan-interface100] mld version 2

[SwitchA-Vlan-interface100] pim ipv6 sm

[SwitchA-Vlan-interface100] quit

[SwitchA] interface vlan-interface 101

[SwitchA-Vlan-interface101] pim ipv6 sm

[SwitchA-Vlan-interface101] quit

[SwitchA] interface vlan-interface 102

[SwitchA-Vlan-interface102] pim ipv6 sm

[SwitchA-Vlan-interface102] quit

3) Configure the IPv6 SSM group range

# Configure the IPv6 SSM group range to be FF3E::/64 on Switch A.

[SwitchA] acl ipv6 number 2000

[SwitchA-acl6-basic-2000] rule permit source ff3e:: 64

[SwitchA-acl6-basic-2000] quit

[SwitchA] pim ipv6

[SwitchA-pim6] ssm-policy 2000

[SwitchA-pim6] quit

The configuration on Switch B, Switch C, Switch D, and Switch E is similar to that on Switch A.

4) Verify the configuration

Use the display pim ipv6 interface command to view the IPv6 PIM configuration and running status on each interface. For example:

# View the IPv6 PIM configuration information on Switch A.

[SwitchA] display pim ipv6 interface

Interface NbrCnt HelloInt DR-Pri DR-Address

Vlan100 0 30 1 1001::1

(local)

Vlan101 1 30 1 1002::2

Vlan102 1 30 1 1003::2

Assume that Host A needs to receive the information a specific IPv6 multicast source S (4001::100/64) sends to IPv6 multicast group G (FF3E::101). Switch A builds an SPT toward the IPv6 multicast source. Switches on the SPT path (Switch A and Switch D) have generated an (S, G) entry, while Switch E, which is not on the SPT path, does not have IPv6 multicast routing entries. You can use the display pim ipv6 routing-table command to view the IPv6 PIM routing table information on each switch. For example:

# View the IPv6 PIM multicast routing table information on Switch A.

[SwitchA] display pim ipv6 routing-table

Total 0 (*, G) entry; 1 (S, G) entry

(4001::100, FF3E::101)

Protocol: pim-ssm, Flag:

UpTime: 00:00:11

Upstream interface: Vlan-interface101

Upstream neighbor: 1002::2

RPF prime neighbor: 1002::2

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface100

Protocol: mld, UpTime: 00:00:11, Expires: 00:03:25

The information on Switch B and Switch C is similar to that on Switch A.

# View the IPv6 PIM multicast routing table information on Switch B.

[SwitchD] display pim ipv6 routing-table

Total 0 (*, G) entry; 1 (S, G) entry

(4001::100, FF3E::101)

Protocol: pim-ssm, Flag: LOC

UpTime: 00:08:02

Upstream interface: Vlan-interface300

Upstream neighbor: NULL

RPF prime neighbor: NULL

Downstream interface(s) information:

Total number of downstreams: 1

1: Vlan-interface105

Protocol: pim-ssm, UpTime: 00:08:02, Expires: 00:03:25

Troubleshooting IPv6 PIM Configuration

Failure of Building a Multicast Distribution Tree Correctly

Symptom

None of the routers in the network (including routers directly connected with IPv6 multicast sources and receivers) has IPv6 multicast forwarding entries. That is, a multicast distribution tree cannot be built correctly and clients cannot receive IPv6 multicast data.

Analysis

l An IPv6 PIM routing entry is created based on an IPv6 unicast route, whichever IPv6 PIM mode is running. Multicast works only when unicast does.

l IPv6 PIM must be enabled on the RPF interface. An RPF neighbor must be an IPv6 PIM neighbor as well. If IPv6 PIM is not enabled on the RPF interface or the RPF neighbor, the establishment of a multicast distribution tree will surely fail, resulting in abnormal multicast forwarding.

l IPv6 PIM requires that the same IPv6 PIM mode, namely DM or SM, must run on the entire network. Otherwise, the establishment of a multicast distribution tree will surely fail, resulting in abnormal multicast forwarding.

Solution

1) Check IPv6 unicast routes. Use the display ipv6 routing-table command to check whether a unicast route exists to the IPv6 multicast source or the RP.

2) Check that the RPF interface is IPv6 PIM enabled. Use the display pim ipv6 interface command to view the IPv6 PIM information on each interface. If IPv6 PIM is not enabled on the interface, use the pim ipv6 dm or pim ipv6 sm command to enable IPv6 PIM.

3) Check that the RPF neighbor is an IPv6 PIM neighbor. Use the display pim ipv6 neighbor command to view the PIM neighbor information.

4) Check that IPv6 PIM and MLD are enabled on the interfaces directly connecting to the IPv6 multicast source and to the receiver.

5) Check that the same IPv6 PIM mode is enabled on related interfaces. Use the display pim ipv6 interface verbose command to check whether the same PIM mode is enabled on the RPF interface and the corresponding interface of the RPF neighbor router.

6) Check that the same IPv6 PIM mode is enabled on all the routers in the entire network. Use the display current-configuration command to check the IPv6 PIM mode information on each interface. Make sure that the same IPv6 PIM mode is enabled on all the routers: IPv6 PIM-SM on all routers, or IPv6 PIM-DM on all routers.

IPv6 Multicast Data Abnormally Terminated on an Intermediate Router

Symptom

An intermediate router can receive IPv6 multicast data successfully, but the data cannot reach the last hop router. An interface on the intermediate router receives data but no corresponding (S, G) entry is created in the IPv6 PIM routing table.

Analysis

l When a router receives an IPv6 multicast packet, it decrements the hop limit value of the IPv6 multicast packet by 1 and recalculates the checksum value. The router then forwards the packet to all outgoing interfaces. If the multicast ipv6 minimum-hoplimit command is configured on the outgoing interfaces, the hop limit value of the packet must be larger than the configured minimum hop limit value; otherwise, the packet will be discarded.

l If an IPv6 multicast forwarding boundary has been configured through the multicast ipv6 boundary command, any IPv6 multicast packet will be kept from crossing the boundary, and therefore no routing entry can be created in the IPv6 PIM routing table.

l In addition, the source-policy command is used to filter received IPv6 multicast packets. If the IPv6 multicast data fails to pass the ACL rule defined in this command, IPv6 PIM cannot create the route entry, either.

Solution

1) Check the minimum hop limit value for IPv6 multicast forwarding. Use the display current-configuration command to check the minimum hop limit value for multicast forwarding. Increase the hop limit value or remove the multicast ipv6 minimum-hoplimit command configured on the interface.

2) Check the IPv6 multicast forwarding boundary configuration. Use the display current-configuration command to check the IPv6 multicast forwarding boundary settings. Use the multicast ipv6 boundary command to change the IPv6 multicast forwarding boundary settings.

3) Check the IPv6 multicast filter configuration. Use the display current-configuration command to check the IPv6 multicast filter configuration. Change the IPv6 ACL rule defined in the source-policy command so that the source/group address of the IPv6 multicast data can pass ACL filtering.

RPs Unable to Join SPT in IPv6 PIM-SM

Symptom

An RPT cannot be established correctly, or the RPs cannot join the SPT to the IPv6 multicast source.

Analysis

l As the core of an IPv6 PIM-SM domain, the RPs serves specific IPv6 multicast groups. Multiple RPs can coexist in a network. Make sure that the RP information on all routers is exactly the same, and a specific group is mapped to the same RP. Otherwise, IPv6 multicast will fail.

l In the case of the static RP mechanism, the same RP address must be configured on all the routers in the entire network, including static RPs, by means of the static RP command. Otherwise, IPv6 multicast will fail.

Solution

1) Check that a route is available to the RP. Carry out the display ipv6 routing-table command to check whether a route is available on each router to the RP.

2) Check the dynamic RP information. Use the display pim ipv6 rp-info command to check whether the RP information is consistent on all routers. In the case of inconsistent RP information, configure consistent RP address on all the routers.

3) Check the static RP configuration. Carry out the display pim ipv6 rp-info command to check whether the same RP address has been configured on all the routers throughout the network.

RPT Establishment Failure or Source Registration Failure in IPv6 PIM-SM

Symptom

C-RPs cannot unicast advertise messages to the BSR. The BSR does not advertise bootstrap messages containing C-RP information and has no unicast route to any C-RP. An RPT cannot be established correctly, or the DR cannot perform source register with the RP.

Analysis

l C-RPs periodically send advertisement messages to the BSR by unicast. If a C-RP does not have a route to the BSR, the BSR will be unable to receive the advertisements from the C-RP, and therefore the bootstrap messages of the BSR will not contain the information about that C-RP.

l The RP is the core of an IPv6 PIM-SM domain. Make sure that the RP information on all routers is exactly the same, a specific group is mapped to the same RP, and a unicast route is available to the RP.

Solution

1) Check whether routes to C-RPs, the RP and the BSR are available. Carry out the display ipv6 routing-table command to check whether routes are available on each router to the RP and the BSR, and whether a route is available between the RP and the BSR. Make sure that each C-RP has a unicast route to the BSR, the BSR has a unicast route to each C-RP, and all the routers in the entire network have a unicast route to the RP.

2) Check the RP and BSR information. IPv6 PIM-SM needs the support of the RP and BSR. Use the display pim ipv6 bsr-info command to check whether the BSR information is available on each router, and then use the display pim ipv6 rp-info command to check whether the RP information is correct.

3) View the IPv6 PIM neighboring relationships. Use the display pim ipv6 neighbor command to check whether the normal neighboring relationships have been established among the routers.

04-IP Multicast Volume

SPT establishment

Graft

RP discovery

Embedded RP

RPT establishment

Switchover to SPT

Assert

Neighbor discovery

DR election

SPT building

Enabling State-Refresh Capability

Configuring C-RP timers globally

Configuring C-BSR parameters globally

Configuring IPv6 Multicast Source Registration

Disabling SPT Switchover

Configuring IPv6 PIM-SSM

Configuring the IPv6 SSM Group Range

Configuring hello options globally

Configuring hello options on an interface

Configuring IPv6 PIM common timers globally

Configuring IPv6 PIM common timers on an interface

Configuring Join/Prune Message Sizes

IPv6 PIM Configuration Examples

Network requirements

Network diagram

Configuration procedure

IPv6 PIM-SM Configuration Example

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Network diagram

Configuration procedure

IPv6 PIM-SSM Configuration Example

Network requirements

Network diagram

Configuration procedure

Troubleshooting IPv6 PIM Configuration

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