HP 6125G User manual

HP 6125 Blade Switch Series
IP Multicast
Configuration Guide
Part number: 5998-3158
Software version: Release 2103
Document version: 6W100-20120907

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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 advantages and applications ·················································································································4
Multicast models································································································································································5
Multicast architecture························································································································································5
Multicast addresses ··················································································································································6
Multicast protocols ···················································································································································9
Multicast packet forwarding mechanism····················································································································· 11
Configuring IGMP snooping ·····································································································································12
Overview········································································································································································· 12
Basic concepts in IGMP snooping······················································································································· 12
How IGMP snooping works ································································································································· 14
IGMP snooping proxying ····································································································································· 15
Protocols and standards ······································································································································· 17
IGMP snooping configuration task list························································································································· 17
Configuring basic IGMP snooping functions ·············································································································· 18
Enabling IGMP snooping ····································································································································· 18
Specifying the version of IGMP snooping ·········································································································· 18
Configuring static multicast MAC address entries····························································································· 19
Configuring IGMP snooping port functions················································································································· 19
Setting aging timers for dynamic ports ··············································································································· 20
Configuring static ports········································································································································· 20
Configuring a port as a simulated member host ······························································································· 21
Enabling IGMP snooping fast-leave processing································································································· 22
Disabling a port from becoming a dynamic router port ··················································································· 22
Configuring IGMP snooping querier ··························································································································· 23
Enabling IGMP snooping querier ························································································································ 23
Configuring parameters for IGMP queries and responses ··············································································· 24
Configuring the source IP addresses for IGMP queries····················································································· 25
Configuring IGMP snooping proxying ························································································································ 25
Enabling IGMP snooping proxying····················································································································· 25
Configuring a source IP address for the IGMP messages sent by the proxy·················································· 26
Configuring an IGMP snooping policy························································································································ 26
Configuring a multicast group filter····················································································································· 26
Configuring multicast source port filtering·········································································································· 27
Enabling dropping unknown multicast data······································································································· 28
Configuring IGMP report suppression ················································································································ 29
Setting the maximum number of multicast groups that a port can join ··························································· 29
Enabling multicast group replacement················································································································ 30
Setting the 802.1p precedence for IGMP messages ························································································ 30
Enabling the IGMP snooping host tracking function ························································································· 31
Setting the DSCP value for IGMP messages······································································································· 31
Displaying and maintaining IGMP snooping·············································································································· 32
IGMP snooping configuration examples ····················································································································· 33
Group policy and simulated joining configuration example············································································ 33

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Static port configuration example ······················································································································· 35
IGMP snooping querier configuration example································································································· 38
IGMP snooping proxying configuration example······························································································ 40
Troubleshooting IGMP snooping ·································································································································· 43
Layer 2 multicast forwarding cannot function ···································································································· 43
Configured multicast group policy fails to take effect ······················································································· 43
Appendix ········································································································································································ 44
Processing of multicast protocol messages ········································································································· 44
Configuring multicast VLANs·····································································································································45
Overview········································································································································································· 45
Multicast VLAN configuration task list ························································································································· 47
Configuring a sub-VLAN-based multicast VLAN········································································································· 47
Configuration guidelines ······································································································································ 47
Configuration procedure ······································································································································ 47
Configuring a port-based multicast VLAN··················································································································· 48
Configuration prerequisites ·································································································································· 48
Configuring user port attributes ··························································································································· 48
Configuring multicast VLAN ports ······················································································································· 49
Displaying and maintaining multicast VLAN··············································································································· 49
Multicast VLAN configuration examples······················································································································ 50
Sub-VLAN-based multicast VLAN configuration example ················································································· 50
Port-based multicast VLAN configuration example···························································································· 54
Configuring multicast routing and forwarding·········································································································57
Overview········································································································································································· 57
RPF check mechanism ··········································································································································· 57
Static multicast routes············································································································································ 59
Multicast forwarding across unicast subnets ······································································································ 61
Multicast traceroute··············································································································································· 61
Configuration task list ···················································································································································· 62
Enabling IP multicast routing········································································································································· 62
Configuring multicast routing and forwarding············································································································ 63
Configuring static multicast routes······················································································································· 63
Configuring a multicast routing policy················································································································ 63
Configuring a multicast forwarding range ········································································································· 64
Configuring the multicast forwarding table size ································································································ 64
Tracing a multicast path ······································································································································· 65
Displaying and maintaining multicast routing and forwarding················································································· 65
Configuration examples ················································································································································ 66
Changing an RPF route········································································································································· 66
Creating an RPF route··········································································································································· 68
Multicast forwarding over a tunnel······················································································································ 70
Troubleshooting multicast routing and forwarding····································································································· 74
Static multicast route failure ································································································································· 74
Multicast data fails to reach receivers················································································································· 74
Configuring IGMP······················································································································································76
Overview········································································································································································· 76
IGMP versions························································································································································ 76
Introduction to IGMPv1········································································································································· 76
Enhancements in IGMPv2····································································································································· 78
Enhancements in IGMPv3····································································································································· 78
IGMP SSM mapping············································································································································· 80
IGMP proxying ······················································································································································ 81
Protocols and standards ······································································································································· 82

iii
IGMP configuration task list ·········································································································································· 82
Configuring basic IGMP functions ······························································································································· 83
Enabling IGMP ······················································································································································ 83
Configuring IGMP versions ·································································································································· 83
Configuring static joining ····································································································································· 84
Configuring a multicast group filter····················································································································· 84
Setting the maximum number of multicast groups that an interface can join ················································· 85
Adjusting IGMP performance ······································································································································· 85
Configuration prerequisites ·································································································································· 85
Configuring Router-Alert option handling methods···························································································· 86
Configuring IGMP query and response parameters·························································································· 87
Configuring IGMP fast-leave processing ············································································································ 89
Enabling the IGMP host tracking function ·········································································································· 89
Setting the DSCP value for IGMP messages······································································································· 89
Configuring IGMP SSM mapping ································································································································ 90
Enabling SSM mapping········································································································································ 90
Configuring SSM mappings································································································································· 90
Configuring IGMP proxying ········································································································································· 90
Enabling IGMP proxying······································································································································ 91
Configuring multicast forwarding on a downstream interface········································································· 91
Displaying and maintaining IGMP······························································································································· 92
IGMP configuration examples ······································································································································ 93
Basic IGMP functions configuration example····································································································· 93
SSM mapping configuration example ················································································································ 95
IGMP proxying configuration example··············································································································· 98
Troubleshooting IGMP·················································································································································100
No membership information on the receiver-side router·················································································100
Inconsistent memberships on routers on the same subnet···············································································101
Configuring PIM······················································································································································ 102
PIM overview ································································································································································102
PIM-DM overview ················································································································································102
PIM-SM overview·················································································································································105
Administrative scoping overview·······················································································································110
PIM-SSM overview···············································································································································112
Relationships among PIM protocols ··················································································································113
Protocols and standards ·····································································································································114
Configuring PIM-DM ····················································································································································114
PIM-DM configuration task list····························································································································114
Configuration prerequisites ································································································································114
Enabling PIM-DM·················································································································································115
Enabling state-refresh capability························································································································115
Configuring state-refresh parameters ················································································································115
Configuring PIM-DM graft retry period·············································································································116
Configuring PIM-SM·····················································································································································117
PIM-SM configuration task list····························································································································117
Configuration prerequisites ································································································································117
Enabling PIM-SM ·················································································································································118
Configuring an RP ···············································································································································118
Configuring a BSR···············································································································································120
Configuring administrative scoping ··················································································································124
Configuring multicast source registration··········································································································126
Disabling the switchover to SPT·························································································································127
Configuring PIM-SSM ··················································································································································127
PIM-SSM configuration task list··························································································································127

iv
Configuration prerequisites ································································································································127
Enabling PIM-SM ·················································································································································127
Configuring the SSM group range····················································································································128
Configuring PIM common features·····························································································································128
PIM common feature configuration task list······································································································129
Configuration prerequisites ································································································································129
Configuring a multicast data filter ·····················································································································129
Configuring a hello message filter ····················································································································130
Configuring PIM hello options ···························································································································130
Configuring the prune delay ······························································································································132
Configuring PIM common timers ·······················································································································132
Configuring join/prune message sizes·············································································································133
Setting the DSCP value for PIM messages ········································································································134
Displaying and maintaining PIM································································································································134
PIM configuration examples ·······································································································································136
PIM-DM configuration example ·························································································································136
PIM-SM non-scoped zone configuration example ···························································································139
PIM-SM admin-scope zone configuration example ·························································································143
PIM-SSM configuration example························································································································149
Troubleshooting PIM ····················································································································································152
A multicast distribution tree cannot be built correctly······················································································152
Multicast data abnormally terminated on an intermediate router··································································153
RPs cannot join SPT in PIM-SM ··························································································································153
RPT establishment failure or source registration failure in PIM-SM ································································154
Configuring MSDP ·················································································································································· 155
Overview·······································································································································································155
How MSDP works ···············································································································································155
Protocols and standards ·····································································································································160
MSDP configuration task list ·······································································································································161
Configuring basic MSDP functions·····························································································································161
Configuration prerequisites ································································································································161
Enabling MSDP····················································································································································161
Creating an MSDP peer connection··················································································································162
Configuring a static RPF peer ····························································································································162
Configuring an MSDP peer connection·····················································································································162
Configuring MSDP peer description··················································································································163
Configuring an MSDP mesh group ···················································································································163
Configuring MSDP peer connection control·····································································································163
Configuring SA messages related parameters ·········································································································164
Configuring SA message content ······················································································································165
Configuring SA request messages·····················································································································165
Configuring SA message filtering rules·············································································································166
Configuring the SA cache mechanism··············································································································167
Displaying and maintaining MSDP ····························································································································167
MSDP configuration examples····································································································································168
PIM-SM Inter-domain multicast configuration ···································································································168
Inter-AS multicast configuration by leveraging static RPF peers ·····································································172
Anycast RP configuration····································································································································176
SA message filtering configuration····················································································································180
Troubleshooting MSDP ················································································································································184
MSDP peers stay in down state ·························································································································184
No SA entries in the switch’s SA cache············································································································184
Inter-RP communication faults in Anycast RP application ················································································185

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Configuring MBGP·················································································································································· 186
MBGP overview····························································································································································186
Protocols and standards ··············································································································································186
MBGP configuration task list·······································································································································186
Configuring basic MBGP functions ····························································································································187
Controlling route advertisement and reception·········································································································187
Configuring MBGP route redistribution·············································································································187
Configuring default route redistribution into MBGP ························································································188
Configuring MBGP route summarization··········································································································189
Advertising a default route to an IPv4 MBGP peer or peer group ································································189
Configuring outbound MBGP route filtering·····································································································190
Configuring inbound MBGP route filtering·······································································································191
Configuring MBGP route dampening ···············································································································192
Configuring MBGP route attributes ····························································································································193
Configuring MBGP route preferences ···············································································································193
Configuring the default local preference ··········································································································193
Configuring the MED attribute ···························································································································193
Configuring the NEXT_HOP attribute················································································································194
Configuring the AS_PATH attributes ·················································································································194
Tuning and optimizing MBGP networks ····················································································································195
Configuring MBGP soft reset······························································································································195
Enabling the MBGP ORF capability ··················································································································196
Configuring the maximum number of MBGP routes for load balancing·······················································197
Configuring a large scale MBGP network ················································································································198
Configuring IPv4 MBGP peer groups················································································································198
Configuring MBGP community ··························································································································198
Configuring an MBGP route reflector ···············································································································199
Displaying and maintaining MBGP ···························································································································200
Displaying MBGP················································································································································200
Resetting MBGP connections······························································································································201
Clearing MBGP information·······························································································································201
MBGP configuration example·····································································································································202
Configuring MLD snooping ···································································································································· 206
Overview·······································································································································································206
Basic concepts in MLD snooping·······················································································································206
How MLD snooping works ·································································································································208
MLD snooping proxying ·····································································································································209
Protocols and standards ·····································································································································211
MLD snooping configuration task list ·························································································································211
Configuring basic MLD snooping functions ··············································································································212
Enabling MLD snooping ·····································································································································212
Specifying the version of MLD snooping ··········································································································212
Configuring IPv6 static multicast MAC address entries···················································································213
Configuring MLD snooping port functions·················································································································213
Configuring aging timers for dynamic ports ····································································································214
Configuring static ports·······································································································································214
Configuring a port as a simulated member host ·····························································································215
Enabling fast-leave processing···························································································································216
Disabling a port from becoming a dynamic router port ·················································································216
Configuring MLD snooping querier ···························································································································217
Enabling MLD snooping querier ························································································································217
Configuring parameters for MLD queries and responses ···············································································218
Configuring the source IPv6 addresses for MLD queries ················································································219
Configuring MLD snooping proxying ························································································································219

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Enabling MLD snooping proxying·····················································································································219
Configuring the source IPv6 addresses for the MLD messages sent by the proxy ·······································220
Configuring an MLD snooping policy························································································································220
Configuring an IPv6 multicast group filter ········································································································220
Configuring IPv6 multicast source port filtering ·······························································································221
Enabling dropping unknown IPv6 multicast data ····························································································222
Configuring MLD report suppression ················································································································222
Setting the maximum number of multicast groups that a port can join ·························································223
Enabling IPv6 multicast group replacement ·····································································································223
Setting the 802.1p precedence for MLD messages ························································································224
Enabling the MLD snooping host tracking function ·························································································225
Setting the DSCP value for MLD messages·······································································································225
Displaying and maintaining MLD snooping··············································································································226
MLD snooping configuration examples ·····················································································································226
IPv6 group policy and simulated joining configuration example ··································································226
Static port configuration example ·····················································································································229
MLD snooping querier configuration example·································································································232
MLD snooping proxying configuration example······························································································234
Troubleshooting MLD snooping ··································································································································237
Layer 2 multicast forwarding cannot function ··································································································237
Configured IPv6 multicast group policy fails to take effect·············································································237
Appendix ······································································································································································238
Processing of IPv6 multicast protocol messages·······························································································238
Configuring IPv6 multicast VLANs ························································································································· 239
Overview·······································································································································································239
IPv6 multicast VLAN configuration task list ···············································································································241
Configuring a sub-VLAN-based IPv6 multicast VLAN ······························································································241
Configuration guidelines ····································································································································241
Configuration procedure ····································································································································241
Configuring a port-based IPv6 multicast VLAN ········································································································242
Configuration prerequisites ································································································································242
Configuring user port attributes ·························································································································242
Configuring IPv6 multicast VLAN ports ·············································································································243
Displaying and maintaining IPv6 multicast VLAN ····································································································243
IPv6 multicast VLAN configuration examples············································································································244
Sub-VLAN-based multicast VLAN configuration example ···············································································244
Port-based multicast VLAN configuration example··························································································248
Configuring IPv6 multicast routing and forwarding ····························································································· 251
Overview·······································································································································································251
RPF check mechanism ·········································································································································251
RPF check implementation in IPv6 multicast ·····································································································252
Configuration task list ··················································································································································253
Enabling IPv6 multicast routing···································································································································253
Configuring IPv6 multicast routing and forwarding ·································································································254
Configuring an IPv6 multicast routing policy ···································································································254
Configuring an IPv6 multicast forwarding range·····························································································254
Configuring the IPv6 multicast forwarding table size······················································································255
Displaying and maintaining IPv6 multicast routing and forwarding ······································································256
Troubleshooting IPv6 multicast policy configuration ································································································257
Abnormal termination of IPv6 multicast data ···································································································257
Configuring MLD····················································································································································· 258
Overview·······································································································································································258
MLD versions························································································································································258

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How MLDv1 works··············································································································································258
How MLDv2 works··············································································································································260
MLD messages ·····················································································································································261
MLD SSM mapping ·············································································································································264
MLD proxying ······················································································································································265
Protocols and standards ·····································································································································265
MLD configuration task list ··········································································································································266
Configuring basic MLD functions ·······························································································································266
Enabling MLD ······················································································································································267
Configuring the MLD version ·····························································································································267
Configuring static joining ···································································································································267
Configuring an IPv6 multicast group filter ········································································································268
Setting the maximum number of IPv6 multicast groups that an interface can join·······································268
Adjusting MLD performance ·······································································································································269
Configuration prerequisites ································································································································269
Configuring Router-Alert option handling methods··························································································269
Configuring MLD query and response parameters··························································································270
Configuring MLD fast-leave processing ············································································································272
Enabling the MLD host tracking function ··········································································································273
Setting the DSCP value for MLD messages·······································································································273
Configuring MLD SSM mapping ································································································································273
Configuration prerequisites ································································································································274
Enabling MLD SSM mapping·····························································································································274
Configuring MLD SSM mappings······················································································································274
Configuring MLD proxying ·········································································································································274
Enabling MLD proxying······································································································································275
Configuring IPv6 multicast forwarding on a downstream interface ······························································275
Displaying and maintaining MLD·······························································································································276
MLD configuration examples ······································································································································277
Basic MLD functions configuration example·····································································································277
MLD SSM mapping configuration example ·····································································································279
MLD proxying configuration example···············································································································282
Troubleshooting MLD ···················································································································································284
No member information on the receiver-side router························································································284
Inconsistent memberships on routers on the same subnet···············································································285
Configuring IPv6 PIM·············································································································································· 286
Overview·······································································································································································286
IPv6 PIM-DM overview········································································································································286
IPv6 PIM-SM overview ········································································································································289
IPv6 administrative scoping overview ···············································································································295
IPv6 PIM-SSM overview ······································································································································297
Relationship among IPv6 PIM protocols············································································································299
Protocols and standards ·····································································································································299
Configuring IPv6 PIM-DM············································································································································299
IPv6 PIM-DM configuration task list ···················································································································299
Configuration prerequisites ································································································································300
Enabling IPv6 PIM-DM ········································································································································300
Enabling state-refresh capability························································································································300
Configuring state refresh parameters················································································································301
Configuring IPv6 PIM-DM graft retry period ····································································································301
Configuring IPv6 PIM-SM ············································································································································302
IPv6 PIM-SM configuration task list····················································································································302
Configuration prerequisites ································································································································302
Enabling IPv6 PIM-SM·········································································································································303

viii
Configuring an RP ···············································································································································303
Configuring a BSR···············································································································································305
Configuring IPv6 administrative scoping ··········································································································309
Configuring IPv6 multicast source registration ·································································································310
Disabling the switchover to SPT·························································································································311
Configuring IPv6 PIM-SSM··········································································································································311
IPv6 PIM-SSM configuration task list ·················································································································312
Configuration prerequisites ································································································································312
Enabling IPv6 PIM-SM·········································································································································312
Configuring the IPv6 SSM group range ···········································································································312
Configuring IPv6 PIM common features ····················································································································313
IPv6 PIM common feature configuration task list ·····························································································313
Configuration prerequisites ································································································································313
Configuring an IPv6 multicast data filter···········································································································314
Configuring a hello message filter ····················································································································314
Configuring IPv6 PIM hello options···················································································································315
Configuring the prune delay ······························································································································316
Configuring IPv6 PIM common timers ···············································································································317
Configuring join/prune message sizes·············································································································318
Setting the DSCP value for IPv6 PIM messages································································································319
Displaying and maintaining IPv6 PIM························································································································319
IPv6 PIM configuration examples ·······························································································································320
IPv6 PIM-DM configuration example·················································································································320
IPv6 PIM-SM non-scoped zone configuration example···················································································323
IPv6 PIM-SM admin-scope zone configuration example·················································································328
IPv6 PIM-SSM configuration example ···············································································································340
Troubleshooting IPv6 PIM configuration ····················································································································343
Failure to build a multicast distribution tree correctly······················································································343
IPv6 multicast data abnormally terminated on an intermediate router··························································344
RPS cannot join SPT in IPv6 PIM-SM ·················································································································344
RPT establishment failure or source registration failure in IPv6 PIM-SM························································345
Configuring IPv6 MBGP ········································································································································· 346
IPv6 MBGP overview ···················································································································································346
IPv6 MBGP configuration task list ······························································································································346
Configuring basic IPv6 MBGP functions····················································································································347
Configuration prerequisites ································································································································347
Configuring an IPv6 MBGP peer·······················································································································347
Configuring a preferred value for routes from a peer or a peer group ························································347
Controlling route distribution and reception ·············································································································348
Configuration prerequisites ································································································································348
Injecting a local IPv6 MBGP route·····················································································································348
Configuring IPv6 MBGP route redistribution ····································································································348
Configuring IPv6 MBGP route summarization ·································································································349
Advertising a default route to a peer or peer group ·······················································································349
Configuring outbound IPv6 MBGP route filtering ····························································································350
Configuring inbound IPv6 MBGP route filtering ······························································································350
Configuring IPv6 MBGP route dampening·······································································································351
Configuring IPv6 MBGP route attributes····················································································································351
Configuration prerequisites ································································································································352
Configuring IPv6 MBGP route preferences·······································································································352
Configuring the default local preference ··········································································································352
Configuring the MED attribute ···························································································································352
Configuring the NEXT_HOP attribute················································································································353
Configuring the AS_PATH attribute ···················································································································353

ix
Tuning and optimizing IPv6 MBGP networks············································································································354
Configuration prerequisites ································································································································354
Configuring IPv6 MBGP soft reset ·····················································································································354
Enabling the IPv6 MBGP orf capability ············································································································355
Configuring the maximum number of equal-cost routes for load-balancing ·················································356
Configuring a large scale IPv6 MBGP network········································································································357
Configuring an IPv6 MBGP peer group ···········································································································357
Configuring IPv6 MBGP community··················································································································357
Configuring an IPv6 MBGP route reflector ·······································································································358
Displaying and maintaining IPv6 MBGP···················································································································359
Displaying IPv6 MBGP········································································································································359
Resetting IPv6 MBGP connections ·····················································································································360
Clearing IPv6 MBGP information ······················································································································360
IPv6 MBGP configuration example ····························································································································360
Support and other resources ·································································································································· 364
Contacting HP ······························································································································································364
Subscription service ············································································································································364
Related information······················································································································································364
Documents····························································································································································364
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Conventions ··································································································································································365
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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 new value-added services, such as
live webcasting, web TV, distance learning, telemedicine, web radio, real time video conferencing, and
other bandwidth-critical and time-critical information services.
The term "router " in this document refers to both routers and Layer 3 switches.
Unless otherwise stated, the term "multicast" in this document refers to IP multicast.
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, assume that Host B, Host D and Host E need the information. A separate transmission channel
must be established from the information source to each of these hosts.
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
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.
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, assume that only Host B, Host D, and Host E need the information. If the information is
broadcast to the subnet, Host A and 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
Unicast and broadcast techniques cannot provide point-to-multipoint data transmissions with the
minimum network consumption.
Multicast transmission can solve this problem. 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.

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 receivers of the information, 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—Because multicast traffic flows to the farthest-possible node from the
source before it is replicated and distributed, an increase in the number of hosts does not increase
the load of the source or remarkably add to the usage of network resources.
•Advantages over broadcast—Because multicast data is sent only to the receivers that need it,
multicast uses network bandwidth reasonably and enhances network security. In addition, data
broadcast is confined to the same subnet, but multicast is not.
Multicast features
•A multicast group is a multicast receiver set identified by an IP multicast address. Hosts join a
multicast group to become members of the multicast group before they can receive the multicast
data addressed to that multicast group. Typically, a multicast source does not need to join a
multicast group.
•An information sender is called a "multicast source". A multicast source can send data to multiple
multicast groups at the same time, and multiple multicast sources can send data to the same
multicast group at the same time.
•All hosts that have joined a multicast group become members of the multicast group. The group
memberships are dynamic. Hosts can join or leave multicast groups at any time. Multicast groups
are not subject to geographic restrictions.
•Routers or Layer 3 switches that support Layer 3 multicast are called "multicast routers" or "Layer 3
multicast devices". In addition to providing the multicast routing function, a multicast router can also
manage multicast group memberships on stub subnets with attached group members. A multicast
router itself can be a multicast group member.

4
For a better understanding of the multicast concept, you can compare multicast transmission to the
transmission of TV programs.
Table 1 Comparing TV program transmission and multicast transmission
TV 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 via the channel.
The receiver starts to receive the multicast data that the
source is sending 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)—Indicates a rendezvous point tree (RPT), or a multicast packet that any multicast source sends
to multicast group G. Here, the asterisk represents any multicast source, and "G" represents a
specific multicast group.
•(S, G)—Indicates a shortest path tree (SPT), or a multicast packet that multicast source S sends to
multicast group G. Here, "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 advantages and applications
Multicast advantages
Advantages of the multicast technique include the following:
•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
The scenarios in which the multicast technique can be effectively applied are:
•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

5
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 sender can send information to a multicast group as a multicast source, and
receivers can join a multicast group (identified by a group address) and obtain multicast information
addressed to that multicast group. In this model, receivers do not know the positions of the multicast
sources in advance. However, they can join or leave the multicast group at any time.
SFM model
The SFM model is derived from the ASM model. To a sender, 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. Therefore,
receivers can receive the multicast data from only part of the multicast sources. To a receiver, multicast
sources are not all valid; they are filtered.
SSM model
Users might be interested in the multicast data from only certain multicast sources. The SSM model
provides a transmission service that enables users to specify the multicast sources that they are interested
in at the client side.
The main difference between the SSM model and the ASM model is that in the SSM model, receivers
have already determined the locations of the multicast sources by some other means. In addition, the
SSM model uses a multicast address range that is different from that of the ASM/SFM model, and
dedicated multicast forwarding paths are established between receivers and the specified multicast
sources.
Multicast architecture
IP multicast addresses the following questions:
•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 should information be 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—A multicast 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—A software 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.

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Multicast addresses
Network-layer multicast addresses (multicast IP addresses) enables communication between multicast
sources and multicast group members. In addition, a technique must be available to map multicast IP
addresses to link-layer multicast MAC addresses.
IP multicast addresses
•IPv4 multicast addresses
Internet Assigned Numbers Authority (IANA) assigned the Class D address space (224.0.0.0 to
239.255.255.255) to IPv4 multicast.
Table 2 Class D IP address blocks and description
Address block Descri
p
tion
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 Time to Live (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, and can be
reused in domains administered by different organizations without
causing conflicts. For more information, see RFC 2365.
NOTE:
"Glop" is a mechanism for assi
g
nin
g
multicast addresses between different autonomous systems (ASs). By
fillin
g
an AS number into the middle two bytes of 233.0.0.0, you
g
et 255 multicast addresses for that AS.
For more information, see RFC 2770.
Table 3 Some reserved multicast addresses
Address Descri
p
tion
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 Distance Vector Multicast Routing Protocol (DVMRP) routers
224.0.0.5 Open Shortest Path First (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 Routing Information Protocol version 2 (RIPv2) routers
224.0.0.11 Mobile agents

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Address Descri
p
tion
224.0.0.12 Dynamic Host Configuration Protocol (DHCP) server/relay agent
224.0.0.13 All Protocol Independent Multicast (PIM) routers
224.0.0.14 Resource Reservation Protocol (RSVP) encapsulation
224.0.0.15 All Core-Based Tree (CBT) routers
224.0.0.16 Designated Subnetwork Bandwidth Management (SBM)
224.0.0.17 All SBMs
224.0.0.18 Virtual Router Redundancy Protocol (VRRP)
•IPv6 multicast addresses
Figure 4 IPv6 multicast format
The following describes the fields of an IPv6 multicast address:
{0xFF—The most significant eight bits are 11111111, which indicates that this address is an IPv6
multicast address.
{Flags—The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit Descri
p
tion
0 Reserved, set to 0.
R
•When set to 0, it indicates that this address is an IPv6 multicast address without an
embedded RP address.
•When set to 1, it indicates that 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, it indicates that this address is an IPv6 multicast address not based on
a unicast prefix.
•When set to 1, it indicates that 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, it indicates that this address is an IPv6 multicast address
permanently-assigned by IANA.
•When set to 1, it indicates that this address is a transient, or dynamically assigned
IPv6 multicast address.
{Scope—The Scope field contains four bits, which indicate the scope of the IPv6 internetwork for
which the multicast traffic is intended.

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Table 5 Values of the Scope field
Value Meanin
g
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—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
A multicast MAC address identifies a group of receivers at the data link layer.
•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 a multicast IPv4 address.
Figure 6 IPv4-to-MAC address mapping
The most significant four bits of a multicast IPv4 address are 1110, which indicates that this
address is a multicast address. Only 23 bits of the remaining 28 bits are mapped to a MAC
address, so five bits of the multicast IPv4 address are lost. As a result, 32 multicast IPv4 addresses
map to the same IPv4 multicast MAC address. Therefore, in Layer 2 multicast forwarding, a switch
might receive some multicast data destined for other IPv4 multicast groups. The upper layer must
filter such redundant data.
•IPv6 multicast MAC addresses
The most significant 16 bits of an IPv6 multicast MAC address are 0x3333. The least significant
32 bits are the least significant 32 bits of a multicast IPv6 address.

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Figure 7 An example of IPv6-to-MAC address mapping
Multicast protocols
Generally, Layer 3 multicast refers to IP multicast working at the network layer. The corresponding
multicast protocols are Layer 3 multicast protocols, which include IGMP, MLD, PIM, IPv6 PIM, MSDP,
MBGP, and IPv6 MBGP. Layer 2 multicast refers to IP multicast working at the data link layer. The
corresponding multicast protocols are Layer 2 multicast protocols, which include IGMP snooping, MLD
snooping, PIM snooping, IPv6 PIM snooping, multicast VLAN, and IPv6 multicast VLAN.
IGMP snooping, PIM snooping, multicast VLAN, IGMP, PIM, MSDP, and MBGP are for IPv4, and MLD
snooping, IPv6 PIM snooping, IPv6 multicast VLAN, MLD, IPv6 PIM, and IPv6 MBGP are for IPv6.
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 8 Positions of Layer 3 multicast protocols
•Multicast group management protocols
Typically, the Internet Group Management Protocol (IGMP) or Multicast Listener Discovery Protocol
(MLD) is used between hosts and Layer 3 multicast devices that directly connect to the hosts. These