H3C S9500 Series User manual

Operation Manual – IPv6 Multicast Routing and Forwarding
H3C S9500 Series Routing Switches Table of Contents
i
Table of Contents
Chapter 1 IPv6 Multicast Routing and Forwarding Configuration ........................................... 1-1
1.1 IPv6 Multicast Routing and Forwarding Overview.............................................................1-1
1.1.1 Introduction to IPv6 Multicast Routing and Forwarding ..........................................1-1
1.1.2 RPF Mechanism......................................................................................................1-2
1.2 Configuration Task List......................................................................................................1-4
1.3 Configuring IPv6 Multicast Routing and Forwarding .........................................................1-4
1.3.1 Enabling IPv6 Multicast Routing .............................................................................1-4
1.3.2 Configuration Prerequisites.....................................................................................1-5
1.3.3 Configuring IPv6 Multicast Load Splitting ...............................................................1-5
1.3.4 Configuring an IPv6 Multicast Forwarding Range...................................................1-5
1.3.5 Configuring the IPv6 Multicast Forwarding Table Size...........................................1-6
1.4 Displaying and Maintaining IPv6 Multicast Routing and Forwarding.................................1-7
1.5 Troubleshooting IPv6 Multicast Policy Configuration ........................................................1-8
1.5.1 Multicast Data Fails to Reach Receivers ................................................................1-8

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Chapter 1 IPv6 Multicast Routing and Forwarding
Configuration
When configuring IPv6 multicast routing and forwarding, go to the following sections for
information you are interested in:
zIPv6 Multicast Routing and Forwarding Overview
zConfiguring IPv6 Multicast Routing and Forwarding
zDisplaying and Maintaining IPv6 Multicast Routing and Forwarding
zTroubleshooting IPv6 Multicast Policy Configuration
Note:
zThe term “router” in this document refers to a router in a generic sense or an S9500
series routing switch running an IPv6 multicast routing protocol.
zCurrently, POS interfaces of S9500 series routing switches do not support IPv6
multicast. The commands to be executed in interface view are not executable in
POS interface view.
1.1 IPv6 Multicast Routing and Forwarding Overview
1.1.1 Introduction to IPv6 Multicast Routing and Forwarding
In IPv6 multicast implementations, multicast routing and forwarding are implemented
by three types of tables:
zEach IPv6 multicast routing protocol has its own multicast routing table, such as
IPv6 PIM routing table.
zThe multicast routing information of different IPv6 multicast routing protocols
forms a general IPv6 multicast routing table.
zThe IPv6 multicast forwarding table is directly used to control the forwarding of
IPv6 multicast packets. This is the table that guides IPv6 multicast forwarding. The
IPv6 multicast forwarding table is consistent with the IPv6 routing table.
An IPv6 multicast forwarding table consists of a set of (S, G) entries, each indicating the
routing information for delivering multicast data from a multicast source to a multicast
group. If a router supports multiple IPv6 multicast protocols, its IPv6 multicast routing
table will include routes generated by these protocols. The router chooses the optimal
route from the IPv6 multicast routing table based on the configured multicast routing

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and forwarding policy and installs the route entry into its IPv6 multicast forwarding
table.
1.1.2 RPF Mechanism
When creating IPv6 multicast routing table entries, an IPv6 multicast routing protocol
uses the reverse path forwarding (RPF) to ensure IPv6 multicast data delivery along
the correct path.
The RPF mechanism enables routers to correctly forward IPv6 multicast packetsbased
on the multicast route configuration. In addition, the RPF mechanism also helps avoid
data loops caused by various reasons.
I. Implementation of the RPF mechanism
Upon receiving an IPv6 multicast packet sent from a multicast source S to an IPv6
multicast group G, the device first searches its IPv6 multicast forwarding table:
1) If the corresponding (S, G) entry exists, and the interface on which the packet
actually arrived is the incoming interface in the IPv6 multicast forwarding table, the
device forwards the packet to all the outgoing interfaces.
2) If the corresponding (S, G) entry exists, but the interface on which the packet
actually arrived is not the incoming interface in the IPv6 multicast forwarding table,
the packet is subject to an RPF check.
zIf the result of the RPF check shows that the RPF interface is the incoming
interface of the existing (S, G) entry, this means that the (S, G) entry is correct but
the packet arrived from a wrong path and is to be discarded.
zIf the result of the RPF check shows that the RPF interface is not the incoming
interface of the existing (S, G) entry, this means that the (S, G) entry is no longer
valid. The device replaces the incoming interface of the (S, G) entry with the
interface on which the packet actually arrived and forwards the packet to all the
outgoing interfaces.
3) If no corresponding (S, G) entry exists in the multicast forwarding table, the packet
is also subject to an RPF check. The device creates an (S, G) entry based on the
relevant routing information and using the RPF interface as the incoming interface,
and installs the entry into the IPv6 multicast forwarding table.
zIf the interface on which the packet actually arrived is the RPF interface, the RPF
check is successful and the device forwards the packet to all the outgoing
interfaces.
zIf the interface on which the packet actually arrived is not the RPF interface, the
RPF check fails and the device discards the packet.
II. RPF Check
The basis for an RPF check is an IPv6 unicast route. The IPv6 unicast routing table
contains the shortest path to each destination subnet. An IPv6 multicast routing

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protocol does not rely on a particular type of IPv6 unicast routes; instead, it relies on the
existing IPv6 unicast routing information in the device to create IPv6 multicast routing
entries.
When performing an RPF check, the device searches its IPv6 unicast routing table
using the IP address of the “packet source” as the destination address and
automatically selects the optimal route as the RPF route. The outgoing interface in the
corresponding routing entry is the RPF interface and the next hop is the RPF neighbor.
The device considers the path along which the IPv6 multicast packet from the RPF
neighbor arrived on the RPF interface to be the shortest path that leads back to the
source.
Note:
The above-mentioned “packet source” can mean different things in different situations:
zFor a packet traveling along the shortest path tree (SPT) from the IPv6 multicast
source to the receivers or to the rendezvous point (RP), “packet source” means the
IPv6 multicast source.
zFor a packet traveling along the rendezvous point tree (RPT) from the RP to the
receivers, “packet source” means the RP.
zFor a bootstrap message from the bootstrap device (BSR), “packet source” means
the BSR.
For details about the concepts of SPT, RPT, RP and BSR, refer to IPv6 PIM
Configuration in the IP Multicast Volume.
Assume that IPv6 unicast routes exist in the network, and IPv6 multicast packets travel
along the SPT from the multicast source to the receivers, as shown in Figure 1-1. The
IPv6 multicast forwarding table on Switch C contains the (S, G) entry, with
VLAN-interface 1 as the RPF interface.

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Figure 1-1 RPF check process
zWhen an IPv6 multicast packet arrives on VLAN-interface 1 of Switch C, as the
interface is the incoming interface of the (S, G) entry, the switch forwards the
packet to all outgoing interfaces.
zWhen an IPv6 multicast packet arrives on VLAN-interface 2 of Switch C, as the
interface is not the incoming interface of the (S, G) entry, the switch performs an
RPF check on the packet: The switch searches its IPv6 unicast routing table and
finds that the outgoing interface to Source (the RPF interface) is VLAN-interface 1.
This means the (S, G) entry is correct and packet arrived along a wrong path. The
RPF check fails and the packet is discarded.
1.2 Configuration Task List
Complete these tasks to configure IPv6 multicast routing and forwarding:
Task Remarks
Enabling IPv6 Multicast Routing Required
Configuring IPv6 Multicast Load Splitting Optional
Configuring an IPv6 Multicast Forwarding Range Optional
Configuring the IPv6 Multicast Forwarding Table Size Optional
1.3 Configuring IPv6 Multicast Routing and Forwarding
1.3.1 Enabling IPv6 Multicast Routing
Before configuring any Layer 3 IPv6 multicast functionality, you must enable IPv6
multicast routing.

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Follow these steps to enable IPv6 multicast routing:
To do… Use the Command… Remarks
Enter system view system-view —
Enable IPv6 multicast
routing multicast ipv6
routing-enable Required
Disabled by default
1.3.2 Configuration Prerequisites
Before configuring IPv6 multicast routing and forwarding, complete the following tasks:
zConfigure an IPv6 unicast routing protocol so that all devices in the domain are
interoperable at the network layer.
zConfigure IPv6 PIM-DM or IPv6 PIM-SM.
Before configuring IPv6 multicast routing and forwarding, prepare the following data:
zMaximum number of downstream nodes for a single IPv6 multicast forwarding
table entry
zMaximum number of entries in the IPv6 multicast forwarding table
1.3.3 Configuring IPv6 Multicast Load Splitting
With the IPv6 multicast load splitting feature enabled, IPv6 multicast traffic will be
evenly distributed among different equal-cost routes.
Follow these steps to enable IPv6 multicast load splitting:
To do... Use the command... Remarks
Enter system view system-view —
Enable IPv6 multicast
load splitting
multicast ipv6
load-splitting {source |
source-group }
Required
Disabled by default
1.3.4 Configuring an IPv6 Multicast Forwarding Range
IPv6 multicast packets do not travel infinitely in a network. The IPv6 multicast data of
each IPv6 multicast group must be transmitted within a definite scope. Presently, you
can define an IPv6 multicast forwarding range by specifying boundary interfaces, which
form a closed IPv6 multicast forwarding area.
You can configure the forwarding boundary for a specific IPv6 multicast group on all
interfaces that support IPv6 multicast forwarding. Amulticast forwarding boundary sets
the boundary condition for the IPv6 multicast groups in the specified range. If the
destination address of an IPv6 multicast packet matches the set boundary condition,

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the packet will not be forwarded. Once an IPv6 multicast boundary is configured on an
interface, this interface can no longer forward IPv6 multicast packets (including those
sent from the local device) or receive IPv6 multicast packets.
Follow these steps to configure an IPv6 multicast forwarding range:
To do... Use the command... Remarks
Enter system view system-view —
Enter VLAN interface view interface interface-type
interface-number —
Configure an IPv6
multicast forwarding
boundary
multicast ipv6 boundary
ipv6-group-address
prefix-length
Required
No forwarding boundary
by default
1.3.5 Configuring the IPv6 Multicast Forwarding Table Size
The device maintains the corresponding forwarding entry for each IPv6 multicast
packet it receives. Excessive IPv6 multicast routing entries can exhaust the device’s
memory and thus result in low performance of the device. You can set a limit on the
number of entries in the IPv6 multicast forwarding table based on the actual networking
situation and the performance requirements.
If the configured maximum number of IPv6 multicast forwarding table entries is smaller
than the current value, the forwarding entries in excess are not immediately deleted;
instead they will be deleted by the IPv6 multicast routing protocol running on the device.
The device will no longer create new IPv6 multicast forwarding entries until the number
of existing IPv6 multicast forwarding entries comes down below the configured value.
If the configured maximum number of downstream nodes for a single IPv6 multicast
forwarding entry is smaller than the current number, the downstream nodes in excess
are not deleted immediately; instead they must be deleted by the IPv6 multicast routing
protocol. The device will no longer create new IPv6 multicast forwarding entries for
newly added downstreamnodes until the number of existing downstream nodes comes
down below the configured value.
Follow these steps to configure the IPv6 multicast forwarding table size:
To do... Use the command... Remarks
Enter system view system-view —
Configure the maximum
number of entries in the
IPv6 multicast forwarding
table
multicast ipv6
forwarding-table
route-limit limit
Optional
256 by default

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To do... Use the command... Remarks
Configure the maximum
number of downstream
nodes for a single IPv6
multicast forwarding table
entry
multicast ipv6
forwarding-table
downstream-limit limit
Optional
128 by default
1.4 Displaying and Maintaining IPv6 Multicast Routing and
Forwarding
To do... Use the command... Remarks
Display the IPv6
multicast boundary
information
display multicast ipv6 boundary
[ ipv6-group-address [ prefix-length ] |
interface interface-type interface-number ]
Available in
any view
Display the information
of the IPv6 multicast
forwarding table
display multicast ipv6 forwarding-table
[ ipv6-source-address [ prefix-length ] |
ipv6-group-address [ prefix-length ] |
incoming-interface { interface-type
interface-number | register } |
outgoing-interface { { exclude | include |
match } { interface-type interface-number |
register } } | statistics | slot slot-id ] *
[ port-info ]
Available in
any view
Display the information
of the IPv6 multicast
routing table
display multicast ipv6 routing-table
[ ipv6-source-address [ prefix-length ]|
ipv6-group-address [ prefix-length ] |
incoming-interface { interface-type
interface-number | register } |
outgoing-interface { { exclude | include |
match } { interface-type interface-number |
register } } ] *
Available in
any view
Display the RPF route
information of the
specified IPv6
multicast source
display multicast ipv6 rpf-info
ipv6-source-address [ ipv6-group-address ] Available in any view
Clear forwarding
entries from the IPv6
multicast forwarding
table
reset multicast ipv6 forwarding-table
{ { ipv6-source-address [ prefix-length ] |
ipv6-group-address [ prefix-length ] |
incoming-interface { interface-type
interface-number | register } } * | all }
Available in
user view
Clear routing entries
from the IPv6 multicast
routing table
reset multicast ipv6 routing-table
{ { ipv6-source-address [ prefix-length ] |
ipv6-group-address [ prefix-length ] |
incoming-interface { interface-type
interface-number | register } } * | all }
Available in
user view

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Caution:
zThe reset command clears the information in the IPv6 multicast routing table or the
multicast forwarding table, and thus may cause transmission failure of IPv6
multicast information.
zWhen a routing entry is deleted from the IPv6 multicast routing table, the
corresponding forwarding entry will also be deleted from the IPv6 multicast
forwarding table.
zWhen a forwarding entry is deleted from the IPv6 multicast forwarding table, the
corresponding routing entry will also be deleted from the IPv6 multicast routing
table.
1.5 Troubleshooting IPv6 Multicast Policy Configuration
1.5.1 Multicast Data Fails to Reach Receivers
I. Symptom
The multicast data can reach some devices but fails to reach the last-hop device.
II. Analysis
If a multicast forwarding boundary is configured on a VLAN interface through the
multicast ipv6 boundary command, any multicast packet will be kept from crossing
the boundary.
III. Solution
1) Use the display pim ipv6 routing-table command to check whether the
corresponding (S, G) entries exist on the device. If so, the device has received the
multicast data; otherwise, the device has not received the data..
2) Use the display multicast ipv6 boundary command to view the multicast
boundary information on the interfaces. .Use the multicast ipv6 boundary
command to change the multicast forwarding boundary setting.
3) In the case of IPv6 PIM-SM, check the BSR and RP information.