HP MSR ASM User manual
HP MSR Router Series
IP Multicast
Configuration Guide(V5)
Part number: 5998-8182
Software version: CMW520-R2513
Document version: 6PW106-20150808
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Legal and notice information
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Contents
Multicast overview ······················································································································································· 1
Overview············································································································································································1
Multicast overview····················································································································································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
Multicast support for VPNs············································································································································ 12
Introduction to VPN instances ······························································································································ 12
Multicast application in VPNs······························································································································ 12
Configuring IGMP······················································································································································14
Overview········································································································································································· 14
IGMP versions························································································································································ 14
IGMPv1 overview·················································································································································· 14
IGMPv2 overview·················································································································································· 16
IGMPv3 overview·················································································································································· 16
IGMP SSM mapping············································································································································· 18
IGMP proxying ······················································································································································ 19
IGMP support for VPNs ········································································································································ 20
Protocols and standards ······································································································································· 20
IGMP configuration task list ·········································································································································· 20
Configuring basic IGMP functions ······························································································································· 21
Configuration prerequisites ·································································································································· 21
Enabling IGMP ······················································································································································ 21
Specifying the IGMP version································································································································ 22
Configuring an interface as a static member interface ····················································································· 22
Configuring a multicast group filter····················································································································· 23
Setting the maximum number of multicast groups that an interface can join ················································· 23
Adjusting IGMP performance ······································································································································· 24
Configuration prerequisites ·································································································································· 24
Configuring Router-Alert option handling methods···························································································· 24
Configuring IGMP query and response parameters·························································································· 25
Enabling IGMP fast-leave processing·················································································································· 27
Enabling the IGMP host tracking function ·········································································································· 28
Configuring IGMP SSM mapping ································································································································ 28
Configuration prerequisites ·································································································································· 29
Enabling SSM mapping········································································································································ 29
Configuring SSM mappings································································································································· 29
Configuring IGMP proxying ········································································································································· 29
Configuration prerequisites ·································································································································· 30
Enabling IGMP proxying······································································································································ 30
Configuring multicast forwarding on a downstream interface········································································· 30
Displaying and maintaining IGMP······························································································································· 31
IGMP configuration examples ······································································································································ 32
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Basic IGMP functions configuration example····································································································· 32
SSM mapping configuration example ················································································································ 34
IGMP proxying configuration example··············································································································· 37
Troubleshooting IGMP··················································································································································· 39
No membership information exists on the receiver-side router ········································································ 39
Membership information is inconsistent on the routers on the same subnet ··················································· 40
Configuring PIM·························································································································································41
Overview········································································································································································· 41
PIM-DM overview ·················································································································································· 41
PIM-SM overview··················································································································································· 44
BIDIR-PIM overview················································································································································ 49
Administrative scoping overview························································································································· 52
PIM-SSM overview················································································································································· 54
Relationship among PIM protocols ······················································································································ 55
PIM support for VPNs············································································································································ 56
Protocols and standards ······································································································································· 56
Configuring PIM-DM ······················································································································································ 56
PIM-DM configuration task list······························································································································ 57
Configuration prerequisites ·································································································································· 57
Enabling PIM-DM··················································································································································· 57
Enabling state-refresh capability·························································································································· 58
Configuring state-refresh parameters ·················································································································· 58
Configuring PIM-DM graft retry period··············································································································· 59
Configuring PIM-SM······················································································································································· 59
PIM-SM configuration task list······························································································································ 60
Configuration prerequisites ·································································································································· 60
Enabling PIM-SM ··················································································································································· 61
Configuring an RP ················································································································································· 62
Configuring a BSR················································································································································· 64
Configuring administrative scoping ···················································································································· 67
Configuring multicast source registration············································································································ 69
Configuring switchover to SPT ····························································································································· 70
Configuring BIDIR-PIM ··················································································································································· 71
BIDIR-PIM configuration task list··························································································································· 71
Configuration prerequisites ·································································································································· 71
Enabling PIM-SM ··················································································································································· 72
Enabling BIDIR-PIM················································································································································ 72
Configuring an RP ················································································································································· 73
Configuring a BSR················································································································································· 75
Configuring administrative scoping ···················································································································· 78
Configuring PIM-SSM ···················································································································································· 80
PIM-SSM configuration task list···························································································································· 80
Configuration prerequisites ·································································································································· 80
Enabling PIM-SM ··················································································································································· 81
Configuring the SSM group range······················································································································ 81
Configuring common PIM features······························································································································· 82
Configuration task list ··········································································································································· 82
Configuration prerequisites ·································································································································· 82
Configuring a multicast data filter ······················································································································· 83
Configuring a hello message filter ······················································································································ 83
Configuring PIM hello options ····························································································································· 84
Setting the prune delay timer ······························································································································· 85
Configuring common PIM timers ························································································································· 86
Configuring join/prune message sizes··············································································································· 87
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Displaying and maintaining PIM·································································································································· 88
PIM configuration examples ········································································································································· 89
PIM-DM configuration example ··························································································································· 89
PIM-SM non-scoped zone configuration example ····························································································· 92
PIM-SM admin-scoped zone configuration example ························································································· 98
BIDIR-PIM configuration example·······················································································································104
PIM-SSM configuration example························································································································108
Troubleshooting PIM ····················································································································································111
A multicast distribution tree cannot be built correctly······················································································111
Multicast data abnormally terminated on an intermediate router··································································112
RPs cannot join SPT in PIM-SM ··························································································································113
RPT establishment failure or source registration failure in PIM-SM ································································114
Configuring multicast routing and forwarding······································································································ 115
Overview·······································································································································································115
RPF check mechanism ·········································································································································115
Static multicast routes··········································································································································117
Multicast forwarding across unicast subnets ····································································································119
Multicast traceroute·············································································································································119
Configuration task list ··················································································································································120
Enabling IP multicast routing·······································································································································120
Configuring multicast routing and forwarding··········································································································121
Configuration prerequisites ································································································································121
Configuring static multicast routes·····················································································································121
Configuring a multicast routing policy··············································································································122
Configuring a multicast forwarding range ·······································································································123
Configuring the multicast forwarding table size ······························································································123
Tracing a multicast path ·····································································································································124
Displaying and maintaining multicast routing and forwarding···············································································125
Configuration examples ··············································································································································126
Changing an RPF route·······································································································································126
Creating an RPF route·········································································································································128
Multicast forwarding over GRE tunnels·············································································································130
Troubleshooting multicast routing and forwarding···································································································133
Static multicast route failure ·······························································································································133
Multicast data fails to reach receivers···············································································································134
Configuring IGMP snooping ·································································································································· 135
Hardware compatibility···············································································································································135
Overview·······································································································································································135
Basic concepts in IGMP snooping·····················································································································135
How IGMP snooping works ·······························································································································137
IGMP snooping proxying ···································································································································138
Protocols and standards ·····································································································································140
IGMP snooping configuration task list·······················································································································140
Configuring basic IGMP snooping functions ············································································································141
Configuration prerequisites ································································································································141
Enabling IGMP snooping ···································································································································141
Specifying the version of IGMP snooping ········································································································141
Configuring IGMP snooping port functions···············································································································142
Configuration prerequisites ································································································································142
Setting aging timers for dynamic ports ·············································································································142
Configuring static ports·······································································································································143
Configuring a port as a simulated member host ·····························································································144
Enabling IGMP snooping fast-leave processing·······························································································145
iv
Disabling a port from becoming a dynamic router port ·················································································145
Configuring IGMP snooping querier ·························································································································146
Configuration prerequisites ································································································································146
Enabling IGMP snooping querier ······················································································································146
Configuring parameters for IGMP queries and responses ·············································································147
Configuring source IP addresses for IGMP queries·························································································148
Configuring IGMP snooping proxying ······················································································································148
Configuration prerequisites ································································································································148
Enabling IGMP snooping proxying···················································································································148
Configuring the source IP addresses for the IGMP messages sent by the proxy··········································149
Configuring IGMP snooping policies·························································································································149
Configuration prerequisites ································································································································149
Configuring a multicast group filter···················································································································149
Configuring multicast source port filtering········································································································150
Enabling dropping unknown multicast data·····································································································151
Enabling IGMP report suppression····················································································································152
Setting the maximum number of multicast groups that a port can join ·························································153
Enabling multicast group replacement··············································································································153
Setting the 802.1p precedence for IGMP messages ······················································································154
Enabling the IGMP snooping host tracking function ·······················································································155
Displaying and maintaining IGMP snooping············································································································155
IGMP snooping configuration examples ···················································································································156
Group policy and simulated joining configuration example··········································································156
Static port configuration example ·····················································································································158
IGMP snooping querier configuration example·······························································································161
IGMP snooping proxying configuration example····························································································163
Troubleshooting IGMP snooping ································································································································166
Layer 2 multicast forwarding cannot function ··································································································166
Appendix ······································································································································································166
Processing of multicast protocol messages ·······································································································166
Configuring MSDP ·················································································································································· 168
Overview·······································································································································································168
How MSDP works ···············································································································································168
MSDP support for VPNs······································································································································173
Protocols and standards ·····································································································································173
MSDP configuration task list ·······································································································································174
Configuring basic MSDP functions·····························································································································174
Configuration prerequisites ································································································································174
Enabling MSDP····················································································································································174
Creating an MSDP peer connection··················································································································175
Configuring a static RPF peer ····························································································································175
Configuring an MSDP peer connection·····················································································································176
Configuration prerequisites ································································································································176
Configuring MSDP peer description··················································································································176
Configuring an MSDP mesh group ···················································································································176
Configuring MSDP peer connection control·····································································································177
Configuring SA message related parameters···········································································································178
Configuration prerequisites ································································································································178
Configuring SA message content ······················································································································178
Configuring SA request messages·····················································································································179
Configuring SA message filtering rules·············································································································179
Configuring the SA cache mechanism··············································································································180
Displaying and maintaining MSDP ····························································································································181
MSDP configuration examples····································································································································181
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PIM-SM Inter-domain multicast configuration ···································································································181
Inter-AS multicast configuration by leveraging static RPF peers ·····································································186
Anycast RP configuration····································································································································191
SA message filtering configuration····················································································································195
Troubleshooting MSDP ················································································································································199
MSDP peers stay in down state ·························································································································199
No SA entries exist in the router's SA cache ···································································································199
No SA entries exist in the router's SA cache ···································································································200
Configuring MBGP·················································································································································· 201
MBGP overview····························································································································································201
Protocols and standards ··············································································································································201
MBGP configuration task list·······································································································································201
Configuring basic MBGP functions ····························································································································202
Configuration prerequisites ································································································································202
Configuration procedure ····································································································································202
Controlling route advertisement and reception·········································································································202
Configuration prerequisites ································································································································202
Configuring MBGP route redistribution·············································································································203
Configuring default route redistribution into MBGP ························································································203
Configuring MBGP route summarization··········································································································204
Advertising a default route to an IPv4 MBGP peer or peer group ································································204
Configuring outbound MBGP route filtering·····································································································205
Configuring inbound MBGP route filtering·······································································································206
Configuring MBGP route dampening ···············································································································207
Configuring MBGP route attributes ····························································································································208
Configuration prerequisites ································································································································208
Configuring MBGP route preferences ···············································································································208
Configuring the default local preference ··········································································································208
Configuring the MED attribute ···························································································································209
Configuring the NEXT_HOP attribute················································································································209
Configuring the AS_PATH attribute ···················································································································210
Optimizing MBGP networks ·······································································································································210
Configuration prerequisites ································································································································211
Configuring MBGP soft reset······························································································································211
Enabling the MBGP ORF capability ··················································································································212
Configuring the maximum number of MBGP routes for load balancing·······················································213
Configuring a large scale MBGP network ················································································································213
Configuration prerequisites ································································································································213
Configuring IPv4 MBGP peer groups················································································································213
Configuring MBGP community ··························································································································214
Configuring an MBGP route reflector ···············································································································215
Displaying and maintaining MBGP ···························································································································216
Displaying MBGP················································································································································216
Resetting MBGP connections······························································································································217
Clearing MBGP information·······························································································································217
MBGP configuration example·····································································································································218
Configuring multicast VPN ····································································································································· 222
Overview·······································································································································································222
MD-VPN overview···············································································································································224
Protocols and standards ·····································································································································227
How MD-VPN works····················································································································································227
Share-MDT establishment ···································································································································227
Share-MDT-based delivery··································································································································231
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MDT switchover ···················································································································································234
Multi-AS MD VPN················································································································································235
Multicast VPN configuration task list··························································································································236
Configuring MD-VPN···················································································································································236
Configuration prerequisites ································································································································236
Enabling IP multicast routing in a VPN instance ······························································································237
Configuring a share-group and an MTI binding······························································································237
Configuring MDT switchover parameters ·········································································································238
Enabling switch-group reuse logging ················································································································238
Configuring BGP MDT·················································································································································239
Configuration prerequisites ································································································································239
Configuring BGP MDT peers or peer groups···································································································239
Configuring a BGP MDT route reflector············································································································240
Displaying and maintaining multicast VPN···············································································································240
Multicast VPN configuration examples······················································································································241
Single-AS MD VPN configuration example······································································································241
Multi-AS MD VPN configuration example ········································································································254
Troubleshooting MD-VPN············································································································································266
A share-MDT cannot be established··················································································································266
An MVRF cannot be created······························································································································267
Configuring MLD····················································································································································· 268
Overview·······································································································································································268
MLD versions························································································································································268
How MLDv1 works··············································································································································268
How MLDv2 works··············································································································································270
MLD message types·············································································································································271
MLD SSM mapping ·············································································································································274
MLD proxying ······················································································································································275
Protocols and standards ·····································································································································275
MLD configuration task list ··········································································································································276
Configuring basic MLD functions ·······························································································································276
Configuration prerequisites ································································································································276
Enabling MLD ······················································································································································277
Configuring the MLD version ·····························································································································277
Configuring static joining ···································································································································277
Configuring an IPv6 multicast group filter ········································································································278
Setting the maximum number of IPv6 multicast groups that an interface can join·······································278
Adjusting MLD performance ·······································································································································279
Configuration prerequisites ································································································································279
Configuring Router-Alert option handling methods··························································································279
Configuring MLD query and response parameters··························································································280
Enabling MLD fast-leave processing··················································································································282
Enabling the MLD host tracking function ··········································································································283
Configuring MLD SSM mapping ································································································································283
Configuration prerequisites ································································································································283
Enabling MLD SSM mapping·····························································································································284
Configuring MLD SSM mapping entries ···········································································································284
Configuring MLD proxying ·········································································································································284
Configuration prerequisites ································································································································284
Enabling MLD proxying······································································································································285
Configuring IPv6 multicast forwarding on a downstream interface ······························································285
Displaying and maintaining MLD·······························································································································286
MLD configuration examples ······································································································································287
Basic MLD functions configuration example·····································································································287
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MLD SSM mapping configuration example ·····································································································289
MLD proxying configuration example···············································································································292
Troubleshooting MLD ···················································································································································294
No member information exists on the receiver-side router ·············································································294
Membership information is inconsistent on the routers on the same subnet ·················································295
Configuring IPv6 PIM·············································································································································· 296
Overview·······································································································································································296
IPv6 PIM-DM overview········································································································································296
IPv6 PIM-SM overview ········································································································································299
IPv6 BIDIR-PIM overview ·····································································································································305
IPv6 administrative scoping overview ···············································································································308
IPv6 PIM-SSM overview ······································································································································310
Relationship among IPv6 PIM protocols············································································································312
Protocols and standards ·····································································································································312
Configuring IPv6 PIM-DM············································································································································312
IPv6 PIM-DM configuration task list ···················································································································312
Configuration prerequisites ································································································································313
Enabling IPv6 PIM-DM ········································································································································313
Enabling state-refresh capability························································································································313
Configuring state-refresh parameters ················································································································314
Configuring IPv6 PIM-DM graft retry period ····································································································314
Configuring IPv6 PIM-SM ············································································································································315
IPv6 PIM-SM configuration task list····················································································································315
Configuration prerequisites ································································································································315
Enabling IPv6 PIM-SM·········································································································································316
Configuring an RP ···············································································································································316
Configuring a BSR···············································································································································319
Configuring IPv6 administrative scoping ··········································································································322
Configuring IPv6 multicast source registration ·································································································323
Configuring switchover to SPT ···························································································································324
Configuring IPv6 BIDIR-PIM·········································································································································325
IPv6 BIDIR-PIM configuration task list ················································································································325
Configuration prerequisites ································································································································325
Enabling IPv6 PIM-SM·········································································································································326
Enabling IPv6 BIDIR-PIM ·····································································································································326
Configuring an RP ···············································································································································326
Configuring a BSR···············································································································································328
Configuring IPv6 administrative scoping ··········································································································332
Configuring IPv6 PIM-SSM··········································································································································333
IPv6 PIM-SSM configuration task list ·················································································································333
Configuration prerequisites ································································································································333
Enabling IPv6 PIM-SM·········································································································································334
Configuring the IPv6 SSM group range ···········································································································334
Configuring common IPv6 PIM features ····················································································································334
Configuration task list ·········································································································································335
Configuration prerequisites ································································································································335
Configuring an IPv6 multicast data filter···········································································································335
Configuring a hello message filter ····················································································································336
Configuring IPv6 PIM hello options···················································································································336
Setting the prune delay timer ·····························································································································338
Configuring common IPv6 PIM timers ···············································································································338
Configuring join/prune message sizes·············································································································340
Configuring IPv6 PIM to work with BFD············································································································340
Displaying and maintaining IPv6 PIM························································································································341
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IPv6 PIM configuration examples ·······························································································································342
IPv6 PIM-DM configuration example·················································································································342
IPv6 PIM-SM non-scoped zone configuration example···················································································345
IPv6 PIM-SM admin-scoped zone configuration example···············································································350
IPv6 BIDIR-PIM configuration example ··············································································································362
IPv6 PIM-SSM configuration example ···············································································································367
Troubleshooting IPv6 PIM············································································································································370
A multicast distribution tree cannot be built correctly······················································································370
IPv6 multicast data is abnormally terminated on an intermediate router ······················································371
RPs cannot join the SPT in IPv6 PIM-SM············································································································372
RPT cannot be established or a source cannot register in IPv6 PIM-SM························································372
Configuring IPv6 multicast routing and forwarding ····························································································· 374
Overview·······································································································································································374
RPF check mechanism ·········································································································································374
RPF check implementation in IPv6 multicast ·····································································································375
IPv6 multicast forwarding across IPv6 unicast subnets····················································································376
Configuration task list ··················································································································································377
Enabling IPv6 multicast routing···································································································································377
Configuring IPv6 multicast routing and forwarding ·································································································377
Configuration prerequisites ································································································································377
Configuring an IPv6 multicast routing policy ···································································································377
Configuring an IPv6 multicast forwarding range·····························································································378
Configuring the IPv6 multicast forwarding table size······················································································379
Displaying and maintaining IPv6 multicast routing and forwarding ······································································380
IPv6 multicast forwarding over GRE tunnel configuration example········································································381
Troubleshooting abnormal termination of IPv6 multicast data ·······································································384
Configuring MLD snooping ···································································································································· 386
Hardware compatibility···············································································································································386
Overview·······································································································································································386
Basic MLD snooping concepts ···························································································································387
How MLD snooping works ·································································································································388
MLD snooping proxying ·····································································································································389
Protocols and standards ·····································································································································391
MLD snooping configuration task list ·························································································································391
Configuring basic MLD snooping functions ··············································································································392
Configuration prerequisites ································································································································392
Enabling MLD snooping ·····································································································································392
Specifying the version of MLD snooping ··········································································································392
Configuring MLD snooping port functions·················································································································393
Configuration prerequisites ································································································································393
Configuring aging timers for dynamic ports ····································································································393
Configuring static ports·······································································································································394
Configuring a port as a simulated member host ·····························································································395
Enabling MLD snooping fast-leave processing·································································································395
Disabling a port from becoming a dynamic router port ·················································································396
Configuring MLD snooping querier ···························································································································397
Configuration prerequisites ································································································································397
Enabling MLD snooping querier ························································································································397
Configuring parameters for MLD queries and responses ···············································································398
Configuring the source IPv6 addresses for MLD queries ················································································398
Configuring MLD snooping proxying ························································································································399
Configuration prerequisites ································································································································399
Enabling MLD snooping proxying·····················································································································399
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Configuring the source IPv6 addresses for the MLD messages sent by the proxy ·······································399
Configuring an MLD snooping policy························································································································400
Configuration prerequisites ································································································································400
Configuring an IPv6 multicast group filter ········································································································400
Configuring IPv6 multicast source port filtering ·······························································································401
Enabling dropping unknown IPv6 multicast data ····························································································402
Enabling MLD report suppression······················································································································403
Setting the maximum number of multicast groups that a port can join ·························································403
Enabling IPv6 multicast group replacement ·····································································································404
Setting the 802.1p precedence for MLD messages ························································································405
Enabling the MLD snooping host tracking function ·························································································406
Displaying and maintaining MLD snooping··············································································································406
MLD snooping configuration examples ·····················································································································407
IPv6 group policy and simulated joining configuration example ··································································407
Static port configuration example ·····················································································································409
MLD snooping querier configuration example·································································································413
MLD snooping proxying configuration example······························································································414
Troubleshooting MLD snooping ··································································································································417
Layer 2 multicast forwarding cannot function ··································································································417
Configured IPv6 multicast group policy fails to take effect·············································································417
Appendix ······································································································································································418
Processing of IPv6 multicast protocol messages·······························································································418
Configuring IPv6 MBGP ········································································································································· 419
IPv6 MBGP overview ···················································································································································419
IPv6 MBGP configuration task list ······························································································································419
Configuring basic IPv6 MBGP functions····················································································································420
Configuration prerequisites ································································································································420
Configuring an IPv6 MBGP peer·······················································································································420
Configuring a preferred value for routes from a peer or a peer group ························································420
Controlling route distribution and reception ·············································································································421
Configuration prerequisites ································································································································421
Injecting a local IPv6 MBGP route·····················································································································421
Configuring IPv6 MBGP route redistribution ····································································································421
Configuring IPv6 MBGP route summarization ·································································································422
Advertising a default route to a peer or peer group ·······················································································422
Configuring outbound IPv6 MBGP route filtering ····························································································423
Configuring inbound IPv6 MBGP route filtering ······························································································423
Configuring IPv6 MBGP route dampening·······································································································424
Configuring IPv6 MBGP route attributes····················································································································425
Configuration prerequisites ································································································································425
Configuring IPv6 MBGP route preferences·······································································································425
Configuring the default local preference ··········································································································425
Configuring the MED attribute ···························································································································425
Configuring the NEXT_HOP attribute················································································································426
Configuring the AS_PATH attribute ···················································································································426
Optimizing IPv6 MBGP networks·······························································································································427
Configuration prerequisites ································································································································427
Configuring IPv6 MBGP soft reset ·····················································································································427
Enabling the IPv6 MBGP ORF capability ·········································································································428
Configuring the maximum number of equal-cost routes for load-balancing ·················································429
Configuring a large scale IPv6 MBGP network········································································································430
Configuration prerequisites ································································································································430
Configuring an IPv6 MBGP peer group ···········································································································430
Configuring IPv6 MBGP community··················································································································430
x
Configuring an IPv6 MBGP route reflector ·······································································································431
Displaying and maintaining IPv6 MBGP···················································································································432
Displaying IPv6 MBGP········································································································································432
Resetting IPv6 MBGP connections ·····················································································································433
Clearing IPv6 MBGP information ······················································································································434
IPv6 MBGP configuration example ····························································································································434
Network requirements·········································································································································434
Configuration procedure ····································································································································435
Support and other resources ·································································································································· 437
Contacting HP ······························································································································································437
Subscription service ············································································································································437
Related information······················································································································································437
Documents····························································································································································437
Websites·······························································································································································437
Conventions ··································································································································································438
Index ········································································································································································ 440
1
Multicast overview
Overview
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.
Unless otherwise stated, the term "multicast"in this document refers to IP multicast.
Multicast overview
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.
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
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
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
As shown in Figure 3, the multicast source sends only one copy of the information to a multicast group.
Host B, Host D, and Host E, which are 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 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
Multicast transmission has the following 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
4
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.
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 through 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)—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)—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
The multicast technique has the following advantages:
•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.
The multicast technique can be use for the following 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
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. Because
not all multicast sources are valid to receivers, 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 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 should information be transmitted to the receivers? (Multicast routing.)
IP multicast is an end-to-end service. The multicast architecture involves the following parts:
1. Addressing mechanism—A multicast source sends information to a group of receivers through a
multicast address.
2. Host registration—Receiver hosts can join and leave multicast groups dynamically. This
mechanism is the basis for management of group memberships.
3. 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.
4. 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.
6
Multicast addresses
Network-layer multicast addresses (namely, 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.
The membership of a group is dynamic. Hosts can join or leave multicast groups at any time.
IP multicast addresses
•IPv4 multicast addresses:
The IANA assigns the Class D address space (224.0.0.0 to 239.255.255.255) for 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 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, and can be
reused in domains administered by different organizations without
causing conflicts. For more information, see RFC 2365.
"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 Some reserved multicast 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 ST routers.
224.0.0.8 ST hosts.
224.0.0.9 RIPv2 routers.
224.0.0.11 Mobile agents.
7
Address Description
224.0.0.12 DHCP server/relay agent.
224.0.0.13 All PIM routers.
224.0.0.14 RSVP encapsulation.
224.0.0.15 All CBT routers.
224.0.0.16 SBM.
224.0.0.17 All SBMs.
224.0.0.18 VRRP.
•IPv6 multicast addresses:
Figure 4 IPv6 multicast format
The following describes the fields of an IPv6 multicast address, as shown in Figure 4:
{0xFF—Contains the most significant eight bits 11111111, which indicates that this address is an
IPv6 multicast address.
{Flags—Contains four bits, as shown in Figure 5 and described in Table 4.
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.
8
{Scope—Contains four bits, which indicate the scope of the IPv6 internetwork for which the
multicast traffic is intended. Table 5 describes the values of the Scope field.
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—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
As shown in Figure 6, the most significant four bits of a multicast IPv4 address are 1110, which
means 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:
As shown in Figure 7, 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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2
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