HP MSR1002-4 User manual

HPE FlexNetwork MSR Router Series
Comware 7 IP Multicast Configuration Guide
Part number: 5200-2392
Software version: MSR-CMW710-R0411
Document version: 6W101-20161114

© Copyright 2016 Hewlett Packard Enterprise Development LP
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Contents
Multicast overview············································································1
Introduction to multicast ················································································································1
Information transmission techniques ·························································································1
Multicast features··················································································································3
Common notations in multicast ································································································4
Multicast benefits and applications····························································································4
Multicast models··························································································································4
Multicast architecture····················································································································5
Multicast addresses···············································································································5
Multicast protocols·················································································································8
Multicast packet forwarding mechanism ························································································· 10
Multicast support for VPNs··········································································································· 10
Introduction to VPN instances································································································ 10
Multicast application in VPNs································································································· 11
Configuring IGMP snooping······························································12
Overview·································································································································· 12
IGMP snooping ports ··········································································································· 12
How IGMP snooping works ··································································································· 14
Protocols and standards······································································································· 15
Compatibility information ············································································································· 15
Feature and hardware compatibility ························································································ 15
Command and hardware compatibility····················································································· 16
IGMP snooping configuration task list ···························································································· 16
Configuring basic IGMP snooping features ····················································································· 17
Enabling IGMP snooping ······································································································ 17
Specifying an IGMP snooping version····················································································· 17
Setting the maximum number of IGMP snooping forwarding entries··············································18
Setting the IGMP last member query interval············································································ 19
Configuring IGMP snooping port features ······················································································· 19
Setting aging timers for dynamic ports····················································································· 19
Configuring static ports········································································································· 20
Configuring a port as a simulated member host········································································· 21
Enabling fast-leave processing ······························································································ 21
Disabling a port from becoming a dynamic router port ································································ 22
Configuring the IGMP snooping querier·························································································· 22
Configuration prerequisites···································································································· 23
Enabling the IGMP snooping querier······················································································· 23
Configuring parameters for IGMP general queries and responses ················································ 23
Configuring parameters for IGMP messages··················································································· 24
Configuration prerequisites···································································································· 24
Configuring source IP addresses for IGMP messages································································24
Setting the 802.1p priority for IGMP messages ········································································· 25
Configuring IGMP snooping policies ······························································································ 26
Configuring a multicast group policy························································································ 26
Enabling multicast source port filtering ···················································································· 27
Enabling dropping unknown multicast data··············································································· 27
Enabling IGMP report suppression ························································································· 28
Setting the maximum number of multicast groups on a port·························································28
Enabling the multicast group replacement feature······································································ 29
Displaying and maintaining IGMP snooping ···················································································· 29
IGMP snooping configuration examples ························································································· 32
Group policy and simulated joining configuration example··························································· 32
Static port configuration example···························································································· 34
IGMP snooping querier configuration example·········································································· 37
Troubleshooting IGMP snooping··································································································· 39
Layer 2 multicast forwarding cannot function ············································································ 39

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Multicast group policy does not work······················································································· 40
Configuring multicast routing and forwarding········································41
Overview·································································································································· 41
RPF check mechanism········································································································· 41
Static multicast routes·········································································································· 43
Multicast forwarding across unicast subnets············································································· 44
Command and hardware compatibility···························································································· 45
Configuration task list·················································································································· 45
Enabling IP multicast routing········································································································ 46
Configuring multicast routing and forwarding··················································································· 46
Configuring static multicast routes ·························································································· 46
Specifying the longest prefix match principle·············································································47
Configuring multicast load splitting·························································································· 47
Configuring a multicast forwarding boundary ············································································47
Configuring static multicast MAC address entries ······································································ 48
Enabling multicast forwarding between sub-VLANs of a super VLAN··················································· 49
Displaying and maintaining multicast routing and forwarding ······························································ 49
Configuration examples··············································································································· 51
Changing an RPF route········································································································ 51
Creating an RPF route ········································································································· 53
Multicast forwarding over a GRE tunnel··················································································· 55
Multicast forwarding over ADVPN tunnels················································································ 58
Troubleshooting multicast routing and forwarding············································································· 64
Static multicast route failure··································································································· 64
Configuring IGMP···········································································65
Overview·································································································································· 65
IGMPv1 overview················································································································ 65
IGMPv2 enhancements········································································································ 66
IGMPv3 enhancements········································································································ 67
IGMP SSM mapping ············································································································ 68
IGMP proxying···················································································································· 69
IGMP support for VPNs········································································································ 70
Protocols and standards······································································································· 70
IGMP configuration task list·········································································································· 71
Configuring basic IGMP features··································································································· 71
Enabling IGMP ··················································································································· 71
Specifying an IGMP version ·································································································· 72
Configuring a static group member ························································································· 72
Configuring a multicast group policy························································································ 72
Adjusting IGMP performance········································································································ 73
Configuring IGMP query and response parameters···································································· 73
Enabling fast-leave processing ······························································································ 75
Configuring IGMP SSM mappings································································································· 76
Configuration prerequisites···································································································· 76
Configuration procedure ······································································································· 76
Configuring IGMP proxying·········································································································· 76
Configuration prerequisites···································································································· 76
Enabling IGMP proxying······································································································· 76
Enabling multicast forwarding on a non-querier interface ···························································· 77
Configuring multicast load splitting on an IGMP proxy ································································77
Enabling IGMP NSR··················································································································· 78
Displaying and maintaining IGMP·································································································· 78
IGMP configuration examples······································································································· 79
Basic IGMP features configuration examples············································································79
IGMP SSM mapping configuration example·············································································· 81
IGMP proxying configuration example····················································································· 84
Troubleshooting IGMP ················································································································ 86
No membership information on the receiver-side router ······························································ 86
Inconsistent membership information on the routers on the same subnet······································· 86

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Configuring PIM·············································································87
Overview·································································································································· 87
PIM-DM overview················································································································ 87
PIM-SM overview················································································································ 89
BIDIR-PIM overview ············································································································ 95
Administrative scoping overview····························································································· 98
PIM-SSM overview············································································································ 100
Relationship among PIM protocols························································································ 101
PIM support for VPNs ········································································································ 102
Protocols and standards····································································································· 102
Configuring PIM-DM················································································································· 102
PIM-DM configuration task list ····························································································· 103
Configuration prerequisites·································································································· 103
Enabling PIM-DM·············································································································· 103
Enabling the state refresh feature························································································· 103
Configuring state refresh parameters ···················································································· 104
Configuring PIM-DM graft retry timer····················································································· 104
Configuring PIM-SM ················································································································· 105
PIM-SM configuration task list······························································································ 105
Configuration prerequisites·································································································· 105
Enabling PIM-SM ·············································································································· 105
Configuring an RP············································································································· 106
Configuring a BSR············································································································· 108
Configuring multicast source registration················································································ 110
Configuring the switchover to SPT························································································ 111
Configuring BIDIR-PIM·············································································································· 111
BIDIR-PIM configuration task list·························································································· 112
Configuration prerequisites·································································································· 112
Enabling BIDIR-PIM··········································································································· 112
Configuring an RP············································································································· 113
Configuring a BSR············································································································· 115
Configuring PIM-SSM ··············································································································· 117
PIM-SSM configuration task list···························································································· 117
Configuration prerequisites·································································································· 117
Enabling PIM-SM ·············································································································· 117
Configuring the SSM group range························································································· 118
Configuring common PIM features ······························································································ 118
Configuration task list········································································································· 118
Configuration prerequisites·································································································· 118
Configuring a multicast source policy ···················································································· 119
Configuring a PIM hello policy······························································································ 119
Configuring PIM hello message options················································································· 119
Configuring common PIM timers ·························································································· 121
Setting the maximum size of each join or prune message ························································· 122
Enabling BFD for PIM ········································································································ 122
Enabling PIM passive mode ································································································ 123
Enabling PIM NSR············································································································· 123
Enabling SNMP notifications for PIM····················································································· 124
Enabling NBMA mode for ADVPN tunnel interfaces································································· 124
Displaying and maintaining PIM·································································································· 125
PIM configuration examples······································································································· 125
PIM-DM configuration example···························································································· 125
PIM-SM non-scoped zone configuration example···································································· 128
PIM-SM admin-scoped zone configuration example································································· 131
BIDIR-PIM configuration example························································································· 136
PIM-SSM configuration example ·························································································· 140
Troubleshooting PIM················································································································· 143
A multicast distribution tree cannot be correctly built ································································ 143
Multicast data is abnormally terminated on an intermediate router ·············································· 144
An RP cannot join an SPT in PIM-SM ··················································································· 144
An RPT cannot be built or multicast source registration fails in PIM-SM······································· 144

iv
Configuring MSDP········································································ 146
Overview································································································································ 146
How MSDP works ············································································································· 146
MSDP support for VPNs····································································································· 151
Protocols and standards····································································································· 151
MSDP configuration task list······································································································· 152
Configuring basic MSDP features································································································ 152
Configuration prerequisites·································································································· 152
Enabling MSDP ················································································································ 152
Specifying an MSDP peer··································································································· 153
Configuring a static RPF peer······························································································ 153
Configuring an MSDP peering connection····················································································· 153
Configuration prerequisites·································································································· 153
Configuring a description for an MSDP peer··········································································· 154
Configuring an MSDP mesh group························································································ 154
Controlling MSDP peering connections·················································································· 154
Configuring SA message-related parameters ················································································ 155
Configuration prerequisites·································································································· 155
Enabling multicast data encapsulation in SA messages···························································· 155
Configuring the originating RP of SA messages ······································································ 156
Configuring SA request messages························································································ 156
Configuring SA message policies ························································································· 157
Configuring the SA cache mechanism··················································································· 158
Displaying and maintaining MSDP······························································································· 158
MSDP configuration examples···································································································· 159
PIM-SM inter-domain multicast configuration·········································································· 159
Inter-AS multicast configuration by leveraging static RPF peers ················································· 163
Anycast RP configuration···································································································· 168
SA message filtering configuration························································································ 171
Troubleshooting MSDP ············································································································· 175
MSDP peers stay in disabled state ······················································································· 175
No SA entries exist in the router's SA message cache······························································ 175
No exchange of locally registered (S, G) entries between RPs··················································· 175
Configuring multicast VPN ····························································· 177
Overview································································································································ 177
MD VPN overview ············································································································· 178
Protocols and standards····································································································· 181
How MD VPN works················································································································· 182
Default-MDT establishment································································································· 182
Default-MDT-based delivery································································································ 185
MDT switchover················································································································ 188
Inter-AS MD VPN·············································································································· 189
M6VPE···························································································································· 192
Multicast VPN configuration task list ···························································································· 193
Configuring MD VPN ················································································································ 194
Configuration prerequisites·································································································· 194
Enabling IP multicast routing for a VPN instance····································································· 194
Creating an MD for a VPN instance ······················································································ 195
Create an MD address family ······························································································ 195
Specifying the default-group································································································ 195
Specifying the MD source interface······················································································· 196
Configuring MDT switchover parameters ··············································································· 196
Configuring the RPF vector feature······················································································· 197
Enabling data-group reuse logging ······················································································· 198
Configuring BGP MDT ·············································································································· 198
Configuration prerequisites·································································································· 198
Configuring BGP MDT peers or peer groups ·········································································· 199
Configuring a BGP MDT route reflector ················································································· 199
Displaying and maintaining multicast VPN ···················································································· 200
Multicast VPN configuration examples ························································································· 201

v
Intra-AS MD VPN configuration example ··············································································· 201
Intra-AS M6VPE configuration example················································································· 214
MD VPN inter-AS option C configuration example ··································································· 229
MD VPN inter-AS option B configuration example···································································· 242
Troubleshooting MD VPN·········································································································· 255
A default-MDT cannot be established···················································································· 255
An MVRF cannot be created ······························································································· 256
Configuring MLD snooping····························································· 257
Overview································································································································ 257
MLD snooping ports··········································································································· 257
How MLD snooping works··································································································· 259
Protocols and standards····································································································· 260
Compatibility information ··········································································································· 260
Feature and hardware compatibility ······················································································ 260
Command and hardware compatibility··················································································· 261
MLD snooping configuration task list···························································································· 261
Configuring basic MLD snooping features····················································································· 262
Enabling MLD snooping······································································································ 262
Specifying an MLD snooping version ···················································································· 262
Setting the maximum number of MLD snooping forwarding entries ············································· 263
Setting the MLD last listener query interval············································································· 264
Configuring MLD snooping port features······················································································· 264
Setting aging timers for dynamic ports··················································································· 264
Configuring static ports······································································································· 265
Configuring a port as a simulated member host······································································· 266
Enabling fast-leave processing ···························································································· 266
Disabling a port from becoming a dynamic router port······························································ 267
Configuring the MLD snooping querier ························································································· 267
Configuration prerequisites·································································································· 268
Enabling the MLD snooping querier ······················································································ 268
Configuring parameters for MLD general queries and responses················································ 268
Configuring parameters for MLD messages ·················································································· 269
Configuration prerequisites·································································································· 269
Configuring source IPv6 addresses for MLD messages···························································· 269
Setting the 802.1p priority for MLD messages········································································· 270
Configuring MLD snooping policies······························································································ 271
Configuring an IPv6 multicast group policy············································································· 271
Enabling IPv6 multicast source port filtering············································································ 272
Enabling dropping unknown IPv6 multicast data······································································ 272
Enabling MLD report suppression························································································· 273
Setting the maximum number of IPv6 multicast groups on a port················································ 273
Enabling the IPv6 multicast group replacement feature····························································· 274
Displaying and maintaining MLD snooping···················································································· 275
MLD snooping configuration examples························································································· 277
IPv6 group policy and simulated joining configuration example ·················································· 277
Static port configuration example·························································································· 279
MLD snooping querier configuration example ········································································· 282
Troubleshooting MLD snooping ·································································································· 285
Layer 2 multicast forwarding cannot function ·········································································· 285
IPv6 multicast group policy does not work·············································································· 285
Configuring IPv6 multicast routing and forwarding······························· 286
Overview································································································································ 286
RPF check mechanism······································································································· 286
IPv6 multicast forwarding across IPv6 unicast subnets····························································· 288
Command and hardware compatibility·························································································· 288
Configuration task list················································································································ 288
Enabling IPv6 multicast routing··································································································· 289
Configuring IPv6 multicast routing and forwarding·········································································· 289
Specifying the longest prefix match principle··········································································· 289
Configuring IPv6 multicast load splitting················································································· 289

vi
Configuring an IPv6 multicast forwarding boundary·································································· 290
Configuring static IPv6 multicast MAC address entries ····························································· 290
Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN ··································· 291
Displaying and maintaining IPv6 multicast routing and forwarding ····················································· 292
Configuration examples············································································································· 294
IPv6 multicast forwarding over a GRE tunnel·········································································· 294
IPv6 multicast forwarding over ADVPN tunnel interfaces··························································· 296
Configuring MLD·········································································· 304
Overview································································································································ 304
How MLDv1 works············································································································· 304
MLDv2 enhancements ······································································································· 306
MLD SSM mapping············································································································ 307
MLD proxying··················································································································· 308
MLD support for VPNs ······································································································· 308
Protocols and standards····································································································· 308
MLD configuration task list········································································································· 309
Configuring basic MLD features·································································································· 309
Enabling MLD··················································································································· 309
Specifying an MLD version·································································································· 310
Configuring a static group member ······················································································· 310
Configuring an IPv6 multicast group policy············································································· 310
Adjusting MLD performance······································································································· 311
Configuring MLD query and response parameters··································································· 311
Enabling fast-leave processing ···························································································· 313
Configuring MLD SSM mappings ································································································ 313
Configuration prerequisites·································································································· 314
Configuration procedure ····································································································· 314
Configuring MLD proxying ········································································································· 314
Configuration prerequisites·································································································· 314
Enabling MLD proxying ······································································································ 314
Enabling IPv6 multicast forwarding on a non-querier interface ··················································· 315
Configuring IPv6 multicast load splitting on an MLD proxy························································· 315
Enabling MLD NSR ·················································································································· 316
Displaying and maintaining MLD································································································· 316
MLD configuration examples······································································································ 317
Basic MLD features configuration examples ··········································································· 317
MLD SSM mapping configuration example············································································· 319
MLD proxying configuration example ···················································································· 322
Troubleshooting MLD················································································································ 323
No member information exists on the receiver-side router························································· 323
Inconsistent membership information on the routers on the same subnet····································· 324
Configuring IPv6 PIM ···································································· 325
Overview································································································································ 325
IPv6 PIM-DM overview······································································································· 325
IPv6 PIM-SM overview ······································································································· 327
IPv6 BIDIR-PIM overview···································································································· 333
IPv6 administrative scoping overview···················································································· 336
IPv6 PIM-SSM overview····································································································· 338
Relationship among IPv6 PIM protocols················································································· 339
IPv6 PIM support for VPNs·································································································· 340
Protocols and standards····································································································· 340
Configuring IPv6 PIM-DM·········································································································· 340
IPv6 PIM-DM configuration task list······················································································· 341
Configuration prerequisites·································································································· 341
Enabling IPv6 PIM-DM······································································································· 341
Enabling the state refresh feature························································································· 341
Configuring state refresh parameters ···················································································· 342
Configuring IPv6 PIM-DM graft retry timer·············································································· 342
Configuring IPv6 PIM-SM ·········································································································· 343
IPv6 PIM-SM configuration task list······················································································· 343

vii
Configuration prerequisites·································································································· 343
Enabling IPv6 PIM-SM ······································································································· 343
Configuring an RP············································································································· 344
Configuring a BSR············································································································· 346
Configuring IPv6 multicast source registration········································································· 348
Configuring the switchover to SPT························································································ 349
Configuring IPv6 BIDIR-PIM······································································································· 349
IPv6 BIDIR-PIM configuration task list··················································································· 349
Configuration prerequisites·································································································· 350
Enabling IPv6 BIDIR-PIM···································································································· 350
Configuring an RP············································································································· 351
Configuring a BSR············································································································· 353
Configuring IPv6 PIM-SSM ········································································································ 355
IPv6 PIM-SSM configuration task list····················································································· 355
Configuration prerequisites·································································································· 355
Enabling IPv6 PIM-SM ······································································································· 355
Configuring the IPv6 SSM group range·················································································· 356
Configuring common IPv6 PIM features ······················································································· 356
Configuration task list········································································································· 356
Configuration prerequisites·································································································· 356
Configuring an IPv6 multicast source policy············································································ 357
Configuring an IPv6 PIM hello policy····················································································· 357
Configuring IPv6 PIM hello message options·········································································· 357
Configuring common IPv6 PIM timers ··················································································· 359
Setting the maximum size of each join or prune message ························································· 360
Enabling BFD for IPv6 PIM·································································································· 361
Enabling IPv6 PIM passive mode ························································································· 361
Enabling IPv6 PIM NSR······································································································ 361
Enabling SNMP notifications for IPv6 PIM·············································································· 362
Enabling NBMA mode for IPv6 ADVPN tunnel interfaces·························································· 362
Displaying and maintaining IPv6 PIM··························································································· 363
IPv6 PIM configuration examples································································································ 364
IPv6 PIM-DM configuration example ····················································································· 364
IPv6 PIM-SM non-scoped zone configuration example····························································· 367
IPv6 PIM-SM admin-scoped zone configuration example·························································· 370
IPv6 BIDIR-PIM configuration example·················································································· 375
IPv6 PIM-SSM configuration example ··················································································· 380
Troubleshooting IPv6 PIM·········································································································· 382
A multicast distribution tree cannot be correctly built ································································ 382
IPv6 multicast data is abnormally terminated on an intermediate router ······································· 383
An RP cannot join an SPT in IPv6 PIM-SM············································································· 383
An RPT cannot be built or IPv6 multicast source registration fails in IPv6 PIM-SM························· 383
Document conventions and icons ···················································· 385
Conventions···························································································································· 385
Network topology icons ············································································································· 386
Support and other resources··························································· 387
Accessing Hewlett Packard Enterprise Support·············································································· 387
Accessing updates··················································································································· 387
Websites ························································································································· 388
Customer self repair ·········································································································· 388
Remote support ················································································································ 388
Documentation feedback ···································································································· 388
Index························································································· 390

1
Multicast overview
Introduction to multicast
As a technique that coexists with unicast and broadcast, the multicast technique effectively
addresses the issue of point-to-multipoint data transmission. By enabling high-efficiency
point-to-multipoint data transmission over a network, multicast greatly saves network bandwidth and
reduces network load.
By using multicast technology, a network operator can easily provide bandwidth-critical and
time-critical information services. These services include live webcasting, Web TV, distance
learning, telemedicine, Web radio, and real-time video conferencing.
Information transmission techniques
The information transmission techniques include unicast, broadcast, and multicast.
Unicast
In unicast transmission, the information source must send a separate copy of information to each
host that needs the information.
Figure 1 Unicast transmission
In Figure 1, Host B, Host D, and Host E need the information. Aseparate transmission channel must
be established from the information source to each of these hosts.
In unicast transmission, the traffic transmitted over the network is proportional to the number of hosts
that need the information. If a large number of hosts need the information, the information source
must send a separate copy of the same information to each of these hosts. Sending many copies
can place a tremendous pressure on the information source and the network bandwidth.
Unicast is not suitable for batch transmission of information.
Source
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for Host B
Packets for Host D
Packets for Host E
IP network

2
Broadcast
In broadcast transmission, the information source sends information to all hosts on the subnet, even
if some hosts do not need the information.
Figure 2 Broadcast transmission
In Figure 2, only Host B, Host D, and Host E need the information. If the information is broadcast to
the subnet, Host Aand Host C also receive it. In addition to information security issues, broadcasting
to hosts that do not need the information also causes traffic flooding on the same subnet.
Broadcast is disadvantageous in transmitting data to specific hosts. Moreover, broadcast
transmission is a significant waste of network resources.
Multicast
Multicast provides point-to-multipoint data transmissions with the minimum network consumption.
When some hosts on the network need multicast information, the information sender, or multicast
source, sends only one copy of the information. Multicast distribution trees are built through multicast
routing protocols, and the packets are replicated only on nodes where the trees branch.
Source
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for all hosts
A network segment

3
Figure 3 Multicast transmission
In Figure 3, the multicast source sends only one copy of the information to a multicast group. Host B,
Host D, and Host E, which are information receivers, must join the multicast group. The routers on
the network duplicate and forward the information based on the distribution of the group members.
Finally, the information is correctly delivered to Host B, Host D, and Host E.
To summarize, multicast has the following advantages:
•
Advantages over unicast—Multicast data is replicated and distributed until it flows to the
farthest-possible node from the source. The increase of receiver hosts will not remarkably
increase the load of the source or the usage of network resources.
•
Advantages over broadcast—Multicast data is sent only to the receivers that need it. This
saves network bandwidth and enhances network security. In addition, multicast data is not
confined to the same subnet.
Multicast features
•
A multicast group is a multicast receiver set identified by an IP multicast address. Hosts must
join a multicast group to become members of the multicast group before they receive the
multicast data addressed to that multicast group. Typically, a multicast source does not need to
join a multicast group.
•
Amulticast source is an information sender. It can send data to multiple multicast groups at the
same time. Multiple multicast sources can send data to the same multicast group at the same
time.
•
The group memberships are dynamic. Hosts can join or leave multicast groups at any time.
Multicast groups are not subject to geographic restrictions.
•
Multicast routers or Layer 3 multicast devices are routers or Layer 3 switches that support Layer
3 multicast. They provide multicast routing and manage multicast group memberships on stub
subnets with attached group members. A multicast router itself can be a multicast group
member.
For a better understanding of the multicast concept, you can compare multicast transmission to the
transmission of TV programs.
Source
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for the multicast group
IP network

4
Table 1 Comparing TV program transmission and multicast transmission
TV program transmission
Multicast transmission
A TV station transmits a TV program through a
channel.
A multicast source sends multicast data to a multicast
group.
A user tunes the TV set to the channel. A receiver joins the multicast group.
The user starts to watch the TV program
transmitted by the TV station on the channel. The receiver starts to receive the multicast data sent by the source to the multicast group.
The user turns off the TV set or tunes to another
channel. The receiver leaves the multicast group or joins another group.
Common notations in multicast
The following notations are commonly used in multicast transmission:
•
(*, G)—Rendezvous point tree (RPT), or a multicast packet that any multicast source sends to
multicast group G. The asterisk (*) represents any multicast source, and "G" represents a
specific multicast group.
•
(S, G)—Shortest path tree (SPT), or a multicast packet that multicast source "S" sends to
multicast group "G." "S" represents a specific multicast source, and "G" represents a specific
multicast group.
For more information about the concepts RPT and SPT, see "Configuring PIM" and "Configuring
IPv6 PIM."
Multicast benefits and applications
Multicast benefits
•
Enhanced efficiency—Reduces the processor load of information source servers and network
devices.
•
Optimal performance—Reduces redundant traffic.
•
Distributed application—Enables point-to-multipoint applications at the price of minimum
network resources.
Multicast applications
•
Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audio
conferencing
•
Communication for training and cooperative operations, such as distance learning and
telemedicine
•
Data warehouse and financial applications (stock quotes)
•
Any other point-to-multipoint application for data distribution
Multicast models
Based on how the receivers treat the multicast sources, the multicast models include any-source
multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).

5
ASM model
In the ASM model, any multicast sources can send information to a multicast group. Receivers can
join a multicast group and get multicast information addressed to that multicast group from any
multicast sources. In this model, receivers do not know the positions of the multicast sources in
advance.
SFM model
The SFM model is derived from the ASM model. To a multicast source, the two models appear to
have the same multicast membership architecture.
The SFM model functionally extends the ASM model. The upper-layer software checks the source
address of received multicast packets and permits or denies multicast traffic from specific sources.
The receivers obtain the multicast data from only part of the multicast sources. To a receiver,
multicast sources are not all valid, but are filtered.
SSM model
The SSM model provides a transmission service that enables multicast receivers to specify the
multicast sources in which they are interested.
In the SSM model, receivers have already determined the locations of the multicast sources. This is
the main difference between the SSM model and the ASM model. In addition, the SSM model uses a
different multicast address range than the ASM/SFM model. Dedicated multicast forwarding paths
are established between receivers and the specified multicast sources.
Multicast architecture
IP multicast addresses the following issues:
•
Where should the multicast source transmit information to? (Multicast addressing.)
•
What receivers exist on the network? (Host registration.)
•
Where is the multicast source that will provide data to the receivers? (Multicast source
discovery.)
•
How is the information transmitted to the receivers? (Multicast routing.)
IP multicast is an end-to-end service. The multicast architecture involves the following parts:
•
Addressing mechanism—A multicast source sends information to a group of receivers
through a multicast address.
•
Host registration—Receiver hosts can join and leave multicast groups dynamically. This
mechanism is the basis for management of group memberships.
•
Multicast routing—Amulticast distribution tree (a forwarding path tree for multicast data on the
network) is constructed for delivering multicast data from a multicast source to receivers.
•
Multicast applications—Asoftware system that supports multicast applications, such as video
conferencing, must be installed on multicast sources and receiver hosts. The TCP/IP stack
must support reception and transmission of multicast data.
Multicast addresses
IP multicast addresses
•
IPv4 multicast addresses:
IANA assigned the Class D address block (224.0.0.0 to 239.255.255.255) to IPv4 multicast.

6
Table 2 Class D IP address blocks and description
Address block Description
224.0.0.0 to 224.0.0.255
Reserved permanent group addresses. The IP address
224.0.0.0 is reserved. Other IP addresses can be used by
routing protocols and for topology searching, protocol
maintenance, and so on. Table 3 lists common permanent
group addresses. A packet destined for an address in this
block will not be forwarded beyond the local subnet regardless
of the TTL value in the IP header.
224.0.1.0 to 238.255.255.255
Globally scoped group addresses. This block includes the
following types of designated group addresses:
•232.0.0.0/8—SSM group addresses.
•233.0.0.0/8—Glop group addresses.
239.0.0.0 to 239.255.255.255
Administratively scoped multicast addresses. These
addresses are considered locally unique rather than globally
unique. You c
an reuse them in domains administered by
different organizations without causing conflicts. For more
information, see RFC 2365.
NOTE:
Glop is a mechanism for assigning multicast addresses between different ASs. By filling an AS
number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS.
For
more information, see RFC 2770.
Table 3 Common permanent multicast group addresses
Address Description
224.0.0.1 All systems on this subnet, including hosts and routers.
224.0.0.2 All multicast routers on this subnet.
224.0.0.3 Unassigned.
224.0.0.4 DVMRP routers.
224.0.0.5 OSPF routers.
224.0.0.6 OSPF designated routers and backup designated routers.
224.0.0.7 Shared Tree (ST) routers.
224.0.0.8 ST hosts.
224.0.0.9 RIPv2 routers.
224.0.0.11 Mobile agents.
224.0.0.12 DHCP server/relay agent.
224.0.0.13 All Protocol Independent Multicast (PIM) routers.
224.0.0.14 RSVP encapsulation.
224.0.0.15 All Core-Based Tree (CBT) routers.
224.0.0.16 Designated SBM.
224.0.0.17 All SBMs.
224.0.0.18 VRRP.
•
IPv6 multicast addresses:

7
Figure 4 IPv6 multicast format
The following describes the fields of an IPv6 multicast address:
0xFF—The most significant eight bits are 11111111.
Flags—The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit
Description
0 Reserved, set to 0.
R
•When set to 0
, this address is an IPv6 multicast
address without an embedded RP address.
•
When set to 1, this address is an IPv6 multicast
address with an embedded RP address. (The P and T
bits must also be set to 1.)
P
•When set to 0
, this address is an IPv6 multicast
address not based on a unicast prefix.
•
When set to 1, this address is an IPv6 multicast
address based on a unicast prefix. (The T bit must also
be set to 1.)
T
•When set to 0
, this address is an IPv6 multicast
address permanently-assigned by IANA.
•When set to 1
, this address is a transient or
dynamically assigned IPv6 multicast address.
Scope—The Scope field contains four bits, which represent the scope of the IPv6
internetwork for which the multicast traffic is intended.
Table 5 Values of the Scope field
Value
Meaning
0, F Reserved.
1 Interface-local scope.
2 Link-local scope.
3 Subnet-local scope.
4 Admin-local scope.
5 Site-local scope.
6, 7, 9 through D Unassigned.
8 Organization-local scope.
Group ID (112 bits)
0xFF Flags Scope
0 7 11 15 31
0RPT

8
Value
Meaning
E Global scope.
Group ID—The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast
group in the scope that the Scope field defines.
Ethernet multicast MAC addresses
•
IPv4 multicast MAC addresses:
As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are
0x01005E. Bit 25 is 0, and the other 23 bits are the least significant 23 bits of an IPv4 multicast
address.
Figure 6 IPv4-to-MAC address mapping
The most significant four bits of an IPv4 multicast address are fixed at 1110. In an IPv4-to-MAC
address mapping, five bits of the IPv4 multicast address are lost. As a result, 32 IPv4 multicast
addresses are mapped to the same IPv4 multicast MAC address. A device might receive
unwanted multicast data at Layer 2 processing, which needs to be filtered by the upper layer.
•
IPv6 multicast MAC addresses:
As defined by IANA, the most significant 16 bits of an IPv6 multicast MAC address are 0x3333.
The least significant 32 bits are mapped from the least significant 32 bits of an IPv6 multicast
address. Therefore, the problem of duplicate IPv6-to-MAC address mapping also arises like
IPv4-to-MAC address mapping.
Figure 7 IPv6-to-MAC address mapping
Multicast protocols
Multicast protocols include the following categories:
•
Layer 3 and Layer 2 multicast protocols:
Layer 3 multicast refers to IP multicast operating at the network layer.
XXXX X
XXXX XXXX XXXX XXXX XXXX XXXX
1110 XXXX
0XXX XXXX XXXX XXXX XXXX XXXX0000 0001 0000 0000 0101 1110
32-bit IPv4 address
48-bit MAC address
5 bits lost
25-bit MAC address prefix
…23 bits
mapped …
FF1E 0000 0000 0000 0000 0000 F30E0101
0101aF30E
48-bit MAC address 3333
32 bits
mapped
128-bit IPv6 address
… …
16-bit MAC
address prefix

9
Layer 3 multicast protocols—IGMP, MLD, PIM, IPv6 PIM, and MSDP.
Layer 2 multicast refers to IP multicast operating at the data link layer.
Layer 2 multicast protocols—IGMP snooping and MLD snooping.
•
IPv4 and IPv6 multicast protocols:
For IPv4 networks—IGMP snooping, IGMP, PIM, and MSDP.
For IPv6 networks—MLD snooping, MLD, and IPv6 PIM.
This section provides only general descriptions about applications and functions of the Layer 2 and
Layer 3 multicast protocols in a network. For more information about these protocols, see the related
chapters.
Layer 3 multicast protocols
In Figure 8, Layer 3 multicast protocols include multicast group management protocols and multicast
routing protocols.
Figure 8 Positions of Layer 3 multicast protocols
•
Multicast group management protocols:
Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) protocol
are multicast group management protocols. Typically, they run between hosts and Layer 3
multicast devices that directly connect to the hosts to establish and maintain multicast group
memberships.
•
Multicast routing protocols:
A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain
multicast routes and correctly and efficiently forward multicast packets. Multicast routes
constitute loop-free data transmission paths (also known as multicast distribution trees) from a
data source to multiple receivers.
In the ASM model, multicast routes include intra-domain routes and inter-domain routes.
An intra-domain multicast routing protocol discovers multicast sources and builds multicast
distribution trees within an AS to deliver multicast data to receivers. Among a variety of
mature intra-domain multicast routing protocols, PIM is most widely used. Based on the
forwarding mechanism, PIM has dense mode (often referred to as PIM-DM) and sparse
mode (often referred to as PIM-SM).
An inter-domain multicast routing protocol is used for delivering multicast information
between two ASs. So far, mature solutions include Multicast Source Discovery Protocol
(MSDP) and MBGP. MSDP propagates multicast source information among different ASs.
AS 1 AS 2
Source
Receiver Receiver
Receiver
PIM/IPv6 PIM PIM/IPv6 PIM
MSDP
IGMP/MLD IGMP/MLD
IGMP/MLD

10
MBGP is an extension of the MP-BGP for exchanging multicast routing information among
different ASs.
For the SSM model, multicast routes are not divided into intra-domain routes and inter-domain
routes. Because receivers know the positions of the multicast sources, channels established
through PIM-SM are sufficient for the transport of multicast information.
Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP snooping and MLD snooping.
IGMP snooping and MLD snooping are multicast constraining mechanisms that run on Layer 2
devices. They manage and control multicast groups by monitoring and analyzing IGMP or MLD
messages exchanged between the hosts and Layer 3 multicast devices. This effectively controls the
flooding of multicast data in Layer 2 networks.
Multicast packet forwarding mechanism
In a multicast model, receiver hosts of a multicast group are usually located at different areas on the
network. They are identified by the same multicast group address. To deliver multicast packets to
these receivers, a multicast source encapsulates the multicast data in an IP packet with the multicast
group address as the destination address. Multicast routers on the forwarding paths forward
multicast packets that an incoming interface receives through multiple outgoing interfaces.
Compared to a unicast model, a multicast model is more complex in the following aspects:
•
To ensure multicast packet transmission on the network, different routing tables are used to
guide multicast forwarding. These routing tables include unicast routing tables, routing tables
for multicast (for example, the MBGP routing table), and static multicast routing tables.
•
To process the same multicast information from different peers received on different interfaces,
the multicast device performs an RPF check on each multicast packet. The RPF check result
determines whether the packet will be forwarded or discarded. The RPF check mechanism is
the basis for most multicast routing protocols to implement multicast forwarding.
For more information about the RPF mechanism, see "Configuring multicast routing and
forwarding" and "Configuring IPv6 multicast routing and forwarding."
Multicast support for VPNs
Multicast support for VPNs refers to multicast applied in VPNs.
Introduction to VPN instances
VPNs are isolated from one another and from the public network. As shown in Figure 9, VPN Aand
VPN B separately access the public network through PE devices.

11
Figure 9 VPN networking diagram
•
The P device belongs to the public network. The CE devices belong to their respective VPNs.
Each CE device serves its own VPN and maintains only one set of forwarding mechanisms.
•
The PE devices connect to the public network and the VPNs. Each PE device must strictly
distinguish the information for different networks, and maintain a separate forwarding
mechanism for each network. On a PE device, a set of software and hardware that serve the
same network forms an instance. Multiple instances can exist on the same PE device, and an
instance can reside on different PE devices. On a PE device, the instance for the public network
is called the public network instance, and those for VPNs are called VPN instances.
Multicast application in VPNs
A PE device that supports multicast for VPNs performs the following operations:
•
Maintains an independent set of multicast forwarding mechanisms for each VPN, including the
multicast protocols, PIM neighbor information, and multicast routing table. In a VPN, the device
forwards multicast data based on the forwarding table or routing table for that VPN.
•
Implements the isolation between different VPNs.
•
Implements information exchange and data conversion between the public network and VPN
instances.
For example, as shown in Figure 9, a multicast source in VPN A sends multicast data to a multicast
group. Only receivers that belong to both the multicast group and VPN A can receive the multicast
data. The multicast data is multicast both in VPN A and on the public network.
VPN A
VPN A
VPN A
VPN BVPN B
Public network
P
PE 1
PE 2
PE 3
CE b3
CE a2
CE a3
CE b1
CE a1
CE b2