HPP Enterprises FlexNetwork 7500 Series User manual

HPE FlexNetwork 7500 Switch Series
IP Multicast Configuration Guide
P
art number: 5200-1936
Software
version: 7500-CMW710-R7524
Document version: 6W100-20161230

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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·······························································································································11
Introduction to VPN instances··················································································································11
Multicast application in VPNs···················································································································12
Configuring IGMP snooping·········································································13
Overview··························································································································································13
IGMP snooping ports ·······························································································································13
How IGMP snooping works······················································································································15
IGMP snooping proxying··························································································································16
Protocols and standards ··························································································································17
Configuration restrictions and guidelines·································································································17
IGMP snooping configuration task list··············································································································17
IGMP snooping configuration task list for VLANs ····················································································18
IGMP configuration task list for VSIs········································································································18
Configuring basic IGMP snooping features ·····································································································19
Enabling IGMP snooping ·························································································································19
Specifying an IGMP snooping version·····································································································20
Setting the maximum number of IGMP snooping forwarding entries·······················································20
Configuring static multicast MAC address entries····················································································21
Setting the IGMP last member query interval ··························································································21
Configuring IGMP snooping port features········································································································22
Setting aging timers for dynamic ports·····································································································22
Configuring static ports ····························································································································23
Configuring a port as a simulated member host ······················································································24
Enabling fast-leave processing················································································································24
Disabling a port from becoming a dynamic router port ············································································25
Configuring the IGMP snooping querier···········································································································25
Configuration prerequisites······················································································································26
Enabling the IGMP snooping querier·······································································································26
Configuring parameters for IGMP general queries and responses··························································26
Enabling IGMP snooping proxying···················································································································27
Configuring parameters for IGMP messages···································································································27
Configuration prerequisites······················································································································27
Configuring the source IP address for IGMP messages··········································································28
Setting the 802.1p priority for IGMP messages ·······················································································29
Configuring IGMP snooping policies················································································································30
Configuring a multicast group policy········································································································30
Enabling multicast source port filtering ····································································································31
Enabling dropping unknown multicast data······························································································31
Enabling IGMP report suppression··········································································································32
Setting the maximum number of multicast groups on a port····································································32
Enabling multicast group replacement·····································································································33
Enabling host tracking······························································································································34
Displaying and maintaining IGMP snooping ····································································································34
IGMP snooping configuration examples ··········································································································36
Group policy and simulated joining configuration example (for VLANs)··················································36

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Static port configuration example (for VLANs)·························································································38
IGMP snooping querier configuration example (for VLANs)····································································40
IGMP snooping proxying configuration example (for VLANs)··································································43
IGMP snooping configuration example (for VXLANs)··············································································44
Troubleshooting IGMP snooping ·····················································································································49
Layer 2 multicast forwarding cannot function···························································································49
Multicast group policy does not work·······································································································50
Configuring PIM snooping············································································51
Overview··························································································································································51
Configuring PIM snooping································································································································52
Displaying and maintaining PIM snooping·······································································································53
PIM snooping configuration example···············································································································53
Network requirements······························································································································53
Configuration procedure···························································································································54
Verifying the configuration························································································································55
Troubleshooting PIM snooping ························································································································57
PIM snooping does not work on a Layer 2 device ···················································································57
Configuring multicast VLANs·······································································58
Overview··························································································································································58
Multicast VLAN configuration task list··············································································································60
Configuring a sub-VLAN-based multicast VLAN······························································································60
Configuration prerequisites······················································································································60
Configuration restrictions and guidelines·································································································60
Configuration procedure···························································································································61
Configuring a port-based multicast VLAN········································································································61
Configuration prerequisites······················································································································61
Configuring user port attributes················································································································61
Assigning user ports to a multicast VLAN································································································62
Setting the maximum number of multicast VLAN forwarding entries·······························································62
Displaying and maintaining multicast VLANs···································································································63
Multicast VLAN configuration examples ··········································································································63
Sub-VLAN-based multicast VLAN configuration example ·······································································63
Port-based multicast VLAN configuration example··················································································66
Configuring multicast routing and forwarding···············································70
Overview··························································································································································70
RPF check mechanism····························································································································70
Static multicast routes······························································································································72
Multicast forwarding across unicast subnets····························································································73
Configuration task list·······································································································································74
Enabling IP multicast routing····························································································································74
Configuring multicast routing and forwarding···································································································75
Configuring static multicast routes···········································································································75
Specifying the longest prefix match principle···························································································75
Configuring multicast load splitting···········································································································76
Configuring a multicast forwarding boundary···························································································76
Enabling multicast forwarding between sub-VLANs of a super VLAN·····························································76
Displaying and maintaining multicast routing and forwarding··········································································77
Configuration examples ···································································································································79
Changing an RPF route ···························································································································79
Creating an RPF route·····························································································································81
Multicast forwarding over a GRE tunnel···································································································82
Troubleshooting multicast routing and forwarding ···························································································85
Static multicast route failure·····················································································································85
Configuring IGMP························································································86
Overview··························································································································································86
IGMPv1 overview·····································································································································86
IGMPv2 enhancements····························································································································87
IGMPv3 enhancements····························································································································88

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IGMP SSM mapping ································································································································89
IGMP proxying ·········································································································································90
IGMP support for VPNs····························································································································91
Protocols and standards ··························································································································91
IGMP configuration task list ·····························································································································92
Configuring basic IGMP features·····················································································································92
Enabling IGMP·········································································································································92
Specifying an IGMP version·····················································································································93
Configuring a static group member··········································································································93
Configuring a multicast group policy········································································································93
Adjusting IGMP performance···························································································································94
Configuring IGMP query and response parameters·················································································94
Enabling fast-leave processing················································································································96
Configuring IGMP SSM mappings···················································································································97
Configuration prerequisites······················································································································97
Configuration procedure···························································································································97
Configuring IGMP proxying······························································································································97
Configuration prerequisites······················································································································97
Enabling IGMP proxying ··························································································································97
Enabling multicast forwarding on a non-querier interface········································································98
Configuring multicast load splitting on an IGMP proxy·············································································98
Enabling IGMP NSR ········································································································································99
Displaying and maintaining IGMP····················································································································99
IGMP configuration examples························································································································100
Basic IGMP features configuration examples························································································100
IGMP SSM mapping configuration example··························································································102
IGMP proxying configuration example···································································································105
Troubleshooting IGMP···································································································································106
No membership information on the receiver-side router········································································106
Inconsistent membership information on the routers on the same subnet·············································106
Configuring PIM·························································································108
Overview························································································································································108
PIM-DM overview···································································································································108
PIM-SM overview···································································································································110
BIDIR-PIM overview·······························································································································116
Administrative scoping overview············································································································119
PIM-SSM overview·································································································································121
Relationship among PIM protocols ········································································································122
PIM support for VPNs ····························································································································123
Protocols and standards ························································································································123
Configuring PIM-DM·······································································································································123
PIM-DM configuration task list ···············································································································124
Configuration prerequisites····················································································································124
Enabling PIM-DM···································································································································124
Enabling the state refresh feature··········································································································124
Configuring state refresh parameters·····································································································125
Configuring PIM-DM graft retry timer·····································································································125
Configuring PIM-SM·······································································································································126
PIM-SM configuration task list················································································································126
Configuration prerequisites····················································································································126
Enabling PIM-SM···································································································································126
Configuring an RP··································································································································127
Configuring a BSR ·································································································································129
Configuring multicast source registration·······························································································131
Configuring the switchover to SPT·········································································································132
Configuration restrictions and guidelines·······························································································132
BIDIR-PIM configuration task list ···········································································································132
Configuration prerequisites····················································································································133
Enabling BIDIR-PIM·······························································································································133
Configuring an RP··································································································································133
Configuring a BSR ·································································································································135

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Configuring PIM-SSM ····································································································································137
PIM-SSM configuration task list·············································································································138
Configuration prerequisites····················································································································138
Enabling PIM-SM···································································································································138
Configuring the SSM group range··········································································································138
Configuring common PIM features·················································································································139
Configuration task list·····························································································································139
Configuration prerequisites····················································································································139
Configuring a multicast source policy·····································································································139
Configuring a PIM hello policy················································································································140
Configuring PIM hello message options·································································································140
Configuring common PIM timers············································································································142
Setting the maximum size of a join or prune message ··········································································143
Enabling BFD for PIM ····························································································································143
Enabling PIM passive mode···················································································································143
Enabling PIM NSR·································································································································144
Enabling SNMP notifications for PIM·····································································································144
Setting a DSCP value for outgoing PIM messages················································································144
Displaying and maintaining PIM·····················································································································145
PIM configuration examples···························································································································145
PIM-DM configuration example··············································································································145
PIM-SM non-scoped zone configuration example ·················································································148
PIM-SM admin-scoped zone configuration example··············································································151
BIDIR-PIM configuration example··········································································································156
PIM-SSM configuration example············································································································160
Troubleshooting PIM······································································································································163
A multicast distribution tree cannot be correctly built·············································································163
Multicast data is abnormally terminated on an intermediate router························································164
An RP cannot join an SPT in PIM-SM····································································································164
An RPT cannot be built or multicast source registration fails in PIM-SM···············································164
Configuring MSDP·····················································································166
Overview························································································································································166
How MSDP works··································································································································166
MSDP support for VPNs ························································································································171
Protocols and standards ························································································································171
MSDP configuration task list··························································································································172
Configuring basic MSDP features··················································································································172
Configuration prerequisites····················································································································172
Enabling MSDP······································································································································172
Specifying an MSDP peer······················································································································173
Configuring a static RPF peer················································································································173
Configuring an MSDP peering connection·····································································································173
Configuration prerequisites····················································································································173
Configuring a description for an MSDP peer··························································································174
Configuring an MSDP mesh group ········································································································174
Controlling MSDP peering connections ·································································································174
Configuring SA message-related parameters································································································175
Configuration prerequisites····················································································································175
Enabling multicast data encapsulation in SA messages········································································175
Configuring the originating RP of SA messages····················································································176
Configuring SA request messages·········································································································176
Configuring SA message policies ··········································································································177
Configuring the SA cache mechanism···································································································178
Enabling MSDP NSR·····································································································································178
Displaying and maintaining MSDP·················································································································178
MSDP configuration examples·······················································································································179
PIM-SM inter-domain multicast configuration ························································································179
Inter-AS multicast configuration by leveraging static RPF peers···························································184
Anycast RP configuration·······················································································································188
SA message filtering configuration·········································································································192
Troubleshooting MSDP··································································································································195

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MSDP peers stay in disabled state········································································································196
No SA entries exist in the router's SA message cache··········································································196
No exchange of locally registered (S, G) entries between RPs·····························································196
Configuring multicast VPN·········································································197
Overview························································································································································197
MD VPN overview··································································································································198
Protocols and standards ························································································································201
How MD VPN works·······································································································································201
Default-MDT establishment····················································································································202
Default-MDT-based delivery ··················································································································205
MDT switchover ·····································································································································208
Inter-AS MD VPN···································································································································209
Configuration restrictions and guidelines·······································································································212
Multicast VPN configuration task list··············································································································212
Configuring MD VPN······································································································································213
Configuration prerequisites····················································································································213
Enabling IP multicast routing for a VPN instance···················································································213
Creating an MD for a VPN instance·······································································································214
Create an MD address family·················································································································214
Specifying the default-group ··················································································································215
Specifying the MD source interface ·······································································································215
Configuring MDT switchover parameters·······························································································216
Configuring the RPF vector feature········································································································216
Enabling data-group reuse logging········································································································217
Configuring BGP MDT ···································································································································217
Configuration prerequisites····················································································································217
Configuring BGP MDT peers or peer groups·························································································217
Configuring a BGP MDT route reflector·································································································218
Displaying and maintaining multicast VPN·····································································································219
Multicast VPN configuration examples···········································································································219
Intra-AS MD VPN configuration example·······························································································219
MD VPN inter-AS option B configuration example·················································································233
MD VPN inter-AS option C configuration example·················································································247
Troubleshooting MD VPN ······························································································································260
A default-MDT cannot be established····································································································260
An MVRF cannot be created··················································································································260
Configuring MLD snooping ········································································262
Overview························································································································································262
MLD snooping ports·······························································································································262
How MLD snooping works ·····················································································································264
MLD snooping proxying ·························································································································265
Protocols and standards ························································································································266
Configuration restrictions and guidelines·······································································································266
MLD snooping configuration task list·············································································································267
MLD snooping configuration task list for VLANs····················································································267
MLD snooping configuration task list for VSIs························································································267
Configuring basic MLD snooping features·····································································································268
Enabling MLD snooping·························································································································268
Specifying an MLD snooping version·····································································································269
Setting the maximum number of MLD snooping forwarding entries ······················································270
Configuring static IPv6 multicast MAC address entries ·········································································270
Setting the MLD last listener query interval····························································································271
Configuring MLD snooping port features ·······································································································271
Setting aging timers for dynamic ports···································································································272
Configuring static ports ··························································································································272
Configuring a port as a simulated member host ····················································································273
Enabling fast-leave processing··············································································································273
Disabling a port from becoming a dynamic router port ··········································································274
Configuring the MLD snooping querier ··········································································································275
Configuration prerequisites····················································································································275

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Enabling the MLD snooping querier·······································································································275
Configuring parameters for MLD general queries and responses ·························································276
Enabling MLD snooping proxying ··················································································································276
Configuring parameters for MLD messages ··································································································277
Configuration prerequisites····················································································································277
Configuring source IPv6 addresses for MLD messages········································································277
Setting the 802.1p priority for MLD messages·······················································································279
Configuring MLD snooping policies················································································································279
Configuring an IPv6 multicast group policy····························································································280
Enabling IPv6 multicast source port filtering··························································································280
Enabling dropping unknown IPv6 multicast data ···················································································281
Enabling MLD report suppression··········································································································282
Setting the maximum number of IPv6 multicast groups on a port··························································282
Enabling IPv6 multicast group replacement···························································································282
Enabling host tracking····························································································································283
Displaying and maintaining MLD snooping····································································································284
MLD snooping configuration examples··········································································································285
IPv6 group policy and simulated joining configuration example (for VLANs)·········································285
Static port configuration example (for VLANs)·······················································································287
MLD snooping querier configuration example (for VLANs)····································································290
MLD snooping proxying configuration example (for VLANs) ·································································293
MLD snooping configuration example (for VXLANs)··············································································294
Troubleshooting MLD snooping·····················································································································299
Layer 2 multicast forwarding cannot function·························································································299
IPv6 multicast group policy does not work·····························································································300
Configuring IPv6 PIM snooping ·································································301
Overview························································································································································301
Configuring IPv6 PIM snooping······················································································································302
Displaying and maintaining IPv6 PIM snooping·····························································································303
IPv6 PIM snooping configuration example (for VLANs)·················································································303
Network requirements····························································································································303
Configuration procedure·························································································································304
Verifying the configuration······················································································································306
Troubleshooting IPv6 PIM snooping··············································································································307
IPv6 PIM snooping does not work on a Layer 2 device·········································································307
Configuring IPv6 multicast VLANs·····························································308
Overview························································································································································308
IPv6 multicast VLAN configuration task list····································································································310
Configuring a sub-VLAN-based IPv6 multicast VLAN ···················································································310
Configuration prerequisites····················································································································310
Configuration guidelines·························································································································310
Configuration procedure·························································································································311
Configuring a port-based IPv6 multicast VLAN······························································································311
Configuration prerequisites····················································································································311
Configuring user port attributes··············································································································311
Assigning user ports to an IPv6 multicast VLAN····················································································312
Setting the maximum number of IPv6 multicast VLAN forwarding entries·····················································312
Displaying and maintaining IPv6 multicast VLANs·························································································313
IPv6 multicast VLAN configuration examples ································································································313
Sub-VLAN-based IPv6 multicast VLAN configuration example·····························································313
Port-based IPv6 multicast VLAN configuration example········································································316
Configuring IPv6 multicast routing and forwarding·····································320
Overview························································································································································320
RPF check mechanism··························································································································320
IPv6 multicast forwarding across IPv6 unicast subnets·········································································322
Configuration task list·····································································································································322
Enabling IPv6 multicast routing······················································································································322
Configuring IPv6 multicast routing and forwarding·························································································323
Specifying the longest prefix match principle·························································································323

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Configuring IPv6 multicast load splitting ································································································323
Configuring an IPv6 multicast forwarding boundary···············································································323
Enabling IPv6 multicast forwarding between sub-VLANs of a super VLAN···········································324
Displaying and maintaining IPv6 multicast routing and forwarding································································324
IPv6 multicast routing and forwarding configuration example········································································326
Network requirements····························································································································326
Configuration procedure·························································································································327
Verifying the configuration······················································································································328
Configuring MLD························································································330
Overview························································································································································330
How MLDv1 works·································································································································330
MLDv2 enhancements···························································································································332
MLD SSM mapping································································································································333
MLD proxying·········································································································································334
MLD support for VPNs···························································································································334
Protocols and standards ························································································································334
MLD configuration task list·····························································································································335
Configuring basic MLD features·····················································································································335
Enabling MLD·········································································································································335
Specifying an MLD version ····················································································································336
Configuring a static group member········································································································336
Configuring an IPv6 multicast group policy····························································································336
Adjusting MLD performance···························································································································337
Configuring MLD query and response parameters················································································337
Enabling fast-leave processing··············································································································339
Configuring MLD SSM mappings···················································································································339
Configuration prerequisites····················································································································340
Configuration procedure·························································································································340
Configuring MLD proxying······························································································································340
Configuration prerequisites····················································································································340
Enabling MLD proxying··························································································································340
Enabling IPv6 multicast forwarding on a non-querier interface······························································341
Configuring IPv6 multicast load splitting on an MLD proxy····································································341
Enabling MLD NSR········································································································································342
Displaying and maintaining MLD····················································································································342
MLD configuration examples··························································································································342
Basic MLD features configuration examples··························································································342
MLD SSM mapping configuration example····························································································345
MLD proxying configuration example·····································································································347
Troubleshooting MLD·····································································································································349
No member information exists on the receiver-side router ····································································349
Inconsistent membership information on the routers on the same subnet·············································349
Configuring IPv6 PIM·················································································350
Overview························································································································································350
IPv6 PIM-DM overview···························································································································350
IPv6 PIM-SM overview···························································································································352
IPv6 BIDIR-PIM overview·······················································································································358
IPv6 administrative scoping overview····································································································361
IPv6 PIM-SSM overview ························································································································363
Relationship among IPv6 PIM protocols································································································364
IPv6 PIM support for VPNs····················································································································365
Protocols and standards ························································································································365
Configuring IPv6 PIM-DM······························································································································365
IPv6 PIM-DM configuration task list·······································································································366
Configuration prerequisites····················································································································366
Enabling IPv6 PIM-DM···························································································································366
Enabling the state refresh feature··········································································································366
Configuring state refresh parameters·····································································································367
Configuring IPv6 PIM-DM graft retry timer·····························································································367
Configuring IPv6 PIM-SM·······························································································································368

viii
IPv6 PIM-SM configuration task list ·······································································································368
Configuration prerequisites····················································································································368
Enabling IPv6 PIM-SM···························································································································368
Configuring an RP··································································································································369
Configuring a BSR ·································································································································371
Configuring IPv6 multicast source registration·······················································································373
Configuring the switchover to SPT·········································································································374
Configuring IPv6 BIDIR-PIM ··························································································································374
Configuration restrictions and guidelines·······························································································374
IPv6 BIDIR-PIM configuration task list···································································································374
Configuration prerequisites····················································································································375
Enabling IPv6 BIDIR-PIM·······················································································································375
Configuring an RP··································································································································375
Configuring a BSR ·································································································································377
Configuring IPv6 PIM-SSM····························································································································379
IPv6 PIM-SSM configuration task list·····································································································379
Configuration prerequisites····················································································································380
Enabling IPv6 PIM-SM···························································································································380
Configuring the IPv6 SSM group range ·································································································380
Configuring common IPv6 PIM features ········································································································381
Configuration task list·····························································································································381
Configuration prerequisites····················································································································381
Configuring an IPv6 multicast source policy ··························································································381
Configuring an IPv6 PIM hello policy ·····································································································382
Configuring IPv6 PIM hello message options ························································································382
Configuring common IPv6 PIM timers····································································································383
Setting the maximum size of a join or prune message ··········································································385
Enabling BFD for IPv6 PIM····················································································································385
Enabling IPv6 PIM passive mode ··········································································································385
Enabling IPv6 PIM NSR·························································································································386
Enabling SNMP notifications for IPv6 PIM·····························································································386
Displaying and maintaining IPv6 PIM·············································································································387
IPv6 PIM configuration examples···················································································································387
IPv6 PIM-DM configuration example······································································································387
IPv6 PIM-SM non-scoped zone configuration example·········································································390
IPv6 PIM-SM admin-scoped zone configuration example ·····································································393
IPv6 BIDIR-PIM configuration example··································································································399
IPv6 PIM-SSM configuration example ···································································································403
Troubleshooting IPv6 PIM······························································································································406
A multicast distribution tree cannot be correctly built·············································································406
IPv6 multicast data is abnormally terminated on an intermediate router ···············································406
An RP cannot join an SPT in IPv6 PIM-SM ···························································································407
An RPT cannot be built or IPv6 multicast source registration fails in IPv6 PIM-SM·······························407
Document conventions and icons······························································408
Conventions···················································································································································408
Network topology icons··································································································································409
Support and other resources ·····································································410
Accessing Hewlett Packard Enterprise Support·····························································································410
Accessing updates·········································································································································410
Websites ················································································································································411
Customer self repair·······························································································································411
Remote support······································································································································411
Documentation feedback ·······················································································································411
Index··········································································································413

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
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).
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

5
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.
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

6
Address block
Description
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 can 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.
E Global scope.
Group ID (112 bits)
0xFF Flags Scope
0 7 11 15 31
0RPT

8
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.
Table 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.
Table 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.
Layer 3 multicast protocols—IGMP, MLD, PIM, IPv6 PIM, MSDP, MBGP, and IPv6
MBGP.
Layer 2 multicast refers to IP multicast operating at the data link layer.
XXXX X
XXXX XXXX XXXX XXXX XXXX XXXX
1110 XXXX
0XXX XXXX XXXX XXXX XXXX XXXX
0000 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 2 multicast protocols—IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM
snooping, multicast VLAN, and IPv6 multicast VLAN.
•
IPv4 and IPv6 multicast protocols:
For IPv4 networks—IGMP snooping, PIM snooping, multicast VLAN, IGMP, PIM, MSDP,
and MBGP.
For IPv6 networks—MLD snooping, IPv6 PIM snooping, IPv6 multicast VLAN, MLD, IPv6
PIM, and IPv6 MBGP.
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
Layer 3 multicast protocols include multicast group management protocols and multicast routing
protocols.
Figure 6 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
MBGP/MSDP
IPv6 MBGP
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, MLD snooping, PIM snooping, IPv6 PIM
snooping, multicast VLAN, and IPv6 multicast VLAN.
Figure 7 Positions of Layer 2 multicast protocols
•
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.
•
PIM snooping and IPv6 PIM snooping:
PIM snooping and IPv6 PIM snooping run on Layer 2 devices. They work with IGMP snooping
or MLD snooping to analyze received PIM messages. Then, they add the ports that are
interested in specific multicast data to a PIM snooping routing entry or IPv6 PIM snooping
routing entry. In this way, multicast data can be forwarded to only the ports that are interested in
the data.
•
Multicast VLAN and IPv6 multicast VLAN:
Multicast VLAN or IPv6 multicast VLAN runs on a Layer 2 device in a multicast network where
multicast receivers for the same group exist in different VLANs. With these protocols, the Layer
3 multicast device sends only one copy of multicast to the multicast VLAN or IPv6 multicast
VLAN on the Layer 2 device. This method avoids waste of network bandwidth and extra burden
on the Layer 3 device.
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
IPv4/IPv6 multicast packets (S1, G1) IPv4/IPv6 multicast packets (S2, G2)
Source 1
Source 2
Receiver
IGMP Snooping
/MLD Snooping
Receiver Receiver
Multicast VLAN
/IPv6 Multicast VLAN
PIM Snooping
/IPv6 PIM Snooping