HP Pavilion a6600 User manual
HP A6600 Routers
IP Multicast
Configuration Guide
Abstract
This document describes the software features for the HP A Series products and guides you through the
software configuration procedures. These configuration guides also provide configuration examples to
help you apply software features to different network scenarios.
This documentation is intended for network planners, field technical support and servicing engineers, and
network administrators working with the HP A Series products.
Part number: 5998-1497
Software version: A6600-CMW520-R2603
Document version: 6PW101-20110630
Legal and notice information
© Copyright 2011 Hewlett-Packard Development Company, L.P.
No part of this documentation may be reproduced or transmitted in any form or by any means without
prior written consent of Hewlett-Packard Development Company, L.P.
The information contained herein is subject to change without notice.
HEWLETT-PACKARD COMPANY MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS
MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS FOR A PARTICULAR PURPOSE. Hewlett-Packard shall not be liable for errors contained
herein or for incidental or consequential damages in connection with the furnishing, performance, or use
of this material.
The only warranties for HP products and services are set forth in the express warranty statements
accompanying such products and services. Nothing herein should be construed as constituting an
additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.
iii
Contents
Configuring IP multicast··············································································································································· 1
Comparing information transmission techniques···········································································································1
Unicast·······································································································································································1
Broadcast ··································································································································································2
Multicast ····································································································································································2
Multicast features ······························································································································································3
Multicast common notations·············································································································································4
Multicast advantages and applications··························································································································4
Multicast models································································································································································5
ASM model ·······························································································································································5
SFM model································································································································································5
SSM model································································································································································5
Multicast architecture························································································································································5
Multicast addresses··················································································································································6
Multicast protocols ···················································································································································9
Multicast packet forwarding mechanism····················································································································· 11
Multi-instance multicast·················································································································································· 11
Multi-instance multicast applications ··················································································································· 12
Configuring IGMP snooping ·····································································································································13
Understanding IGMP snooping ···································································································································· 15
Receiving a general query ··································································································································· 15
Receiving a membership report··························································································································· 15
Receiving a leave message ·································································································································· 16
Protocols and standards ······································································································································· 17
Configuring IGMP snooping basic functions ·············································································································· 18
Prerequisites ··························································································································································· 18
Enabling IGMP snooping ····································································································································· 18
Configuring IGMP snooping version··················································································································· 18
Configuring IGMP forwarding entries················································································································· 19
Configuring IGMP snooping port functions················································································································· 19
Prerequisites ··························································································································································· 19
Configuring aging timers for dynamic ports ······································································································ 19
Configuring static ports········································································································································· 20
Configuring simulated joining······························································································································ 21
Configuring fast leave processing ······················································································································· 22
Disabling a port or a group of ports from changing into dynamic router ports············································· 22
Configuring IGMP snooping querier ··························································································································· 23
Prerequisites ··························································································································································· 23
Enabling IGMP snooping querier························································································································ 23
Configuring IGMP queries and responses·········································································································· 24
Configuring source IP address of IGMP queries································································································ 25
Configuring IGMP snooping proxying ························································································································ 25
Prerequisites ··························································································································································· 25
Enabling IGMP snooping proxying····················································································································· 25
Configuring a source IP address for the IGMP messages sent by the proxy·················································· 26
Configuring an IGMP snooping policy························································································································ 26
Prerequisites ··························································································································································· 26
Configuring a multicast group filter····················································································································· 26
Configuring multicast source port filtering·········································································································· 27
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Configuring the function of dropping unknown multicast data········································································ 28
Configuring IGMP report suppression ················································································································ 28
Configuring maximum multicast groups that can be joined on a port ···························································· 29
Configuring multicast group replacement··········································································································· 29
Configuring 802.1p precedence for IGMP messages······················································································ 30
Enabling Configuring a multicast user control policy························································································ 30
Displaying and maintaining IGMP snooping·············································································································· 31
IGMP snooping configuration examples ····················································································································· 32
Group policy and simulated joining configuration example············································································ 32
Static port configuration example ······················································································································· 34
IGMP snooping querier configuration example································································································· 38
IGMP snooping proxying configuration example······························································································ 40
Troubleshooting IGMP snooping configuration ·········································································································· 42
Layer 2 multicast forwarding cannot function ···································································································· 42
Configured multicast group policy fails to take effect ······················································································· 43
Processing multicast protocol messages ············································································································· 43
Configuring multicast routing and forwarding·········································································································44
Multicast routing and forwarding overview ················································································································ 44
RPF check mechanism··········································································································································· 44
Multicast static routes············································································································································ 46
Application of GRE tunnel in multicast forwarding···························································································· 48
Multicast traceroute··············································································································································· 48
Enabling IP multicast routing········································································································································· 49
Configuring multicast routing and forwarding············································································································ 50
Prerequisites ··························································································································································· 50
Configuring multicast static routes······················································································································· 50
Configuring a multicast routing policy················································································································ 50
Configuring a multicast forwarding range ········································································································· 51
Configuring the multicast forwarding table size ································································································ 52
Configuring static multicast MAC address entries····························································································· 53
Tracing a multicast path ······································································································································· 53
Displaying and maintaining multicast routing and forwarding ················································································ 54
Configuration examples ················································································································································ 55
Changing an RPF route········································································································································· 55
Creating an RPF route··········································································································································· 57
Multicast forwarding over a GRE tunnel············································································································· 59
Troubleshooting multicast routing and forwarding····································································································· 63
Multicast static route failure·································································································································· 63
Configuring IGMP······················································································································································64
IGMP overview······························································································································································· 64
IGMP versions························································································································································ 64
Introduction to IGMPv1········································································································································· 64
Enhancements in IGMPv2 ···································································································································· 66
Enhancements in IGMPv3 ···································································································································· 66
IGMP SSM mapping············································································································································· 68
IGMP proxying ······················································································································································ 69
Multi-instance IGMP ·············································································································································· 70
Protocols and standards ······································································································································· 70
Configuring basic functions of IGMP··························································································································· 70
Prerequisites ··························································································································································· 70
Enabling IGMP ······················································································································································ 71
Configuring IGMP versions ·································································································································· 71
Configuring static joining ····································································································································· 72
Configuring a multicast group filter····················································································································· 73
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Configuring the maximum number of multicast groups on an interface·························································· 73
Adjusting IGMP performance ······································································································································· 73
Prerequisites ··························································································································································· 73
Configuring IGMP message options ··················································································································· 74
Configuring IGMP query and response parameters ························································································· 75
Configuring IGMP fast leave processing············································································································ 77
Enabling the IGMP host tracking function ·········································································································· 78
Configuring IGMP SSM mapping ································································································································ 78
Prerequisites ··························································································································································· 78
Enabling SSM mapping········································································································································ 79
Configuring SSM mappings································································································································· 79
Configuring IGMP proxying ········································································································································· 79
Prerequisites ··························································································································································· 79
Enabling IGMP proxying······································································································································ 79
Configuring multicast forwarding on a downstream interface········································································· 80
Displaying and maintaining IGMP Displaying and maintaining IGMP··································································· 81
IGMP configuration examples ······································································································································ 82
Basic IGMP functions configuration example····································································································· 82
SSM mapping configuration example ················································································································ 85
IGMP proxying configuration example··············································································································· 88
Troubleshooting IGMP··················································································································································· 89
No membership information on the receiver-side router··················································································· 89
Inconsistent memberships on routers on the same subnet················································································· 90
Configuring PIM·························································································································································91
Understanding PIM-DM ················································································································································· 91
Neighbor discovery ·············································································································································· 92
SPT building ··························································································································································· 92
Graft ······································································································································································· 93
Assert ······································································································································································ 94
Understanding PIM-SM·················································································································································· 94
Neighbor discovery ·············································································································································· 95
DR election ····························································································································································· 95
RP discovery··························································································································································· 96
RPT building ··························································································································································· 98
Multicast source registration ································································································································ 99
Switchover to SPT ·················································································································································· 99
Assert ····································································································································································100
Understanding BIDIR-PIM ············································································································································100
Neighbor discovery ············································································································································101
RP discovery·························································································································································101
DF election ···························································································································································101
Bidirectional RPT building···································································································································102
Administrative scoping ·······································································································································103
Understanding PIM-SSM ·············································································································································105
Neighbor discovery ············································································································································105
DR election ···························································································································································105
Construction of SPT ·············································································································································106
PIM protocol relationships···········································································································································106
Multi-instance PIM ···············································································································································107
Protocols and standards ··············································································································································107
Configuring PIM-DM····················································································································································107
Prerequisites ·························································································································································107
Enabling PIM-DM ················································································································································108
Enabling state-refresh capability························································································································109
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Configuring state-refresh parameters ················································································································109
Configuring PIM-DM graft retry period·············································································································110
Configuring PIM-SM············································································································································110
Configuration prerequisites································································································································110
Enabling PIM-SM·················································································································································111
Configuring an RP ···············································································································································111
Configuring a BSR···············································································································································113
Configuring administrative scoping ··················································································································117
Configuring multicast source registration ·········································································································118
Disabling SPT switchover····································································································································119
Configuring BIDIR-PIM ·················································································································································119
Prerequisites ·························································································································································119
Enabling PIM-SM·················································································································································120
Enabling BIDIR-PIM··············································································································································121
Configuring an RP ···············································································································································121
Configuring a BSR···············································································································································123
Configuring administrative scoping ··················································································································126
Configuring PIM-SSM ·········································································································································128
Prerequisites ·························································································································································128
Enabling PIM-SM·················································································································································128
Configuring the SSM group range····················································································································129
Configuring PIM common features·····························································································································130
Configuration prerequisites································································································································130
Configuring a multicast data filter ·····················································································································130
Configuring a hello message filter ····················································································································131
Configuring PIM hello options ···························································································································131
Configuring the prune delay ······························································································································133
Configuring PIM common timers ·······················································································································133
Configuring join/prune message sizes·············································································································134
Displaying and maintaining PIM································································································································135
PIM configuration examples ·······································································································································136
PIM-DM configuration example ·························································································································136
PIM-SM non-scoped zone configuration example ···························································································140
PIM-SM admin-scope zone configuration example ·························································································145
BIDIR-PIM configuration example ······················································································································151
PIM-SSM configuration example ·······················································································································156
Troubleshooting PIM configuration ····························································································································159
Failure to build a multicast distribution tree correctly······················································································159
Multicast data abnormally terminated on an intermediate router··································································160
RPs unable to join SPT in PIM-SM······················································································································161
RPT establishment failure or source registration failure in PIM-SM ································································161
Configuring MSDP ·················································································································································· 163
MSDP peers ··································································································································································163
Multi-instance MSDP ···········································································································································168
Protocols and standards ·····································································································································168
Configuring basic functions of MSDP ························································································································168
Prerequisites ·························································································································································168
Enabling MSDP····················································································································································169
Creating an MSDP peer connection··················································································································169
Configuring a static RPF peer ····························································································································170
Configuring an MSDP peer connection·····················································································································170
Prerequisites ·························································································································································170
Configuring MSDP peer description ·················································································································170
Configuring an MSDP mesh group ···················································································································171
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Configuring MSDP peer connection control·····································································································171
Configuring SA messages related parameters ·········································································································172
Prerequisites ·························································································································································172
Configuring SA message content·······························································································································172
Configuring SA request messages·····················································································································173
Configuring SA message filtering rules·············································································································173
Configuring the SA cache mechanism··············································································································174
Displaying and maintaining MSDP ···················································································································175
MSDP configuration examples ···································································································································175
Inter-AS multicast configuration leveraging BGP routes ··················································································175
Inter-AS multicast configuration leveraging static RPF peers ··········································································180
Anycast RP configuration····································································································································184
SA message filtering configuration ···················································································································188
Troubleshooting MSDP ················································································································································192
MSDP peers stay in down state ·························································································································192
No SA entries in the router SA cache···············································································································192
Inter-RP communication faults in Anycast RP application················································································193
Configuring MBGP·················································································································································· 194
Protocols and standards ··············································································································································194
Configuring MBGP basic functions····························································································································194
Prerequisites ·························································································································································194
Procedure ·····························································································································································194
Controlling route advertisement and reception·········································································································195
Prerequisites ·························································································································································195
Configuring MBGP route redistribution·············································································································195
Configure default route redistribution into MBGP····························································································195
Configuring MBGP route summarization··········································································································196
Advertising a default route to an IPv4 MBGP peer or peer group ································································196
Configuring outbound MBGP route filtering·····································································································197
Configuring inbound MBGP route filtering·······································································································197
Configuring MBGP route dampening ···············································································································198
Configuring MBGP route attributes ····························································································································199
Prerequisites ·························································································································································199
Configuring MBGP route preferences···············································································································199
Configuring the default local preference ··········································································································199
Configuring the MED attribute···························································································································199
Configuring the next hop attribute·····················································································································200
Configuring the AS-PATH attribute ····················································································································201
Tuning and optimizing MBGP networks····················································································································201
Prerequisites ·························································································································································201
Configuring MBGP soft reset······························································································································201
Enabling the MBGP ORF capability··················································································································202
Configuring the maximum number of MBGP routes for load balancing·······················································204
Configuring a large scale MBGP network ················································································································204
Prerequisites ·························································································································································204
Configuring IPv4 MBGP peer groups ···············································································································204
Configuring MBGP community ··························································································································205
Configuring an MBGP route reflector ···············································································································205
Displaying and maintaining MBGP ···························································································································206
Resetting MBGP connections······························································································································207
Clearing MBGP information·······························································································································207
MBGP configuration example ····································································································································208
Configuring multicast VPN ····································································································································· 212
Introduction to Multicast VPN·····························································································································213
viii
Introduction to MD-VPN······································································································································214
Basic concepts in MD-VPN·································································································································214
Introduction to multicast across VPNs ···············································································································217
Protocols and standards ·····································································································································220
Implementing MD-VPN ················································································································································220
Establishing share-MDT·······································································································································220
Share-MDT-based delivery ·································································································································223
MDT switchover ···················································································································································226
Multi-AS MD VPN················································································································································227
Configuring MD-VPN···················································································································································228
Configuration prerequisites································································································································228
Enabling IP multicast routing in a VPN instance ······························································································229
Configuring a share-group and an MTI binding······························································································229
Configuring MDT switchover parameters ·········································································································230
Enabling switch-group reuse logging················································································································230
Configuring BGP MDT·················································································································································231
Configuration prerequisites································································································································231
Configuring BGP MDT peers or peer groups···································································································231
Configuring a BGP MDT route reflector············································································································231
Specifying the source IP address for multicast across VPNs ···················································································232
Configuration prerequisites································································································································232
Configuration procedure ····································································································································232
Displaying and maintaining multicast VPN···············································································································233
Multicast VPN configuration examples······················································································································233
Single-AS MD VPN configuration······················································································································233
Multi-AS MD VPN configuration························································································································246
Troubleshooting MD-VPN configuration ····················································································································260
A share-MDT cannot be established ·················································································································260
Unable to build an MVRF···································································································································260
Configuring IPv6 multicast routing and forwarding ····························································································· 262
RPF check mechanism·········································································································································262
Enabling IPv6 multicast routing ··································································································································264
Configuring IPv6 multicast routing and forwarding ·································································································264
Prerequisites ·························································································································································264
Configuring an IPv6 multicast routing policy ···································································································265
Configuring an IPv6 multicast forwarding range·····························································································265
Configuring the IPv6 multicast forwarding table size······················································································265
Configuring IPv6 Static multicast MAC address entries··················································································266
Displaying and maintaining IPv6 multicast routing and forwarding ······································································267
Troubleshooting IPv6 multicast policy configuration ································································································268
Abnormal termination of IPv6 multicast data ···································································································268
Configuring MLD····················································································································································· 270
MLD versions ································································································································································270
MLDv1 operation ·························································································································································270
MLD querier election···········································································································································270
MLDv2 operation·················································································································································272
MLD message types ············································································································································273
MLD SSM mapping·············································································································································276
MLD proxying ······················································································································································277
Protocols and standards ··············································································································································278
Configuring basic functions of MLD···························································································································278
Prerequisites ·························································································································································278
Enabling MLD ······················································································································································278
Configuring the MLD version ·····························································································································278
ix
Configuring static joining ···································································································································279
Configuring an IPv6 multicast group filter ········································································································280
Configuring the maximum number of IPv6 multicast groups on an interface ···············································280
Adjusting MLD performance ·······································································································································280
Prerequisites ·························································································································································280
Configuring MLD message options ···················································································································281
Configuring MLD query and response parameters··························································································282
Configuring MLD fast leave processing ············································································································284
Enabling the MLD host tracking function ··········································································································285
Configuring MLD SSM mapping ································································································································285
Configuration prerequisites································································································································285
Enabling MLD SSM mapping·····························································································································286
Configuring MLD SSM mapping ·······················································································································286
Configuring MLD proxying ·········································································································································286
Configuration prerequisites································································································································286
Enabling MLD proxying······································································································································286
Configuring IPv6 multicast forwarding on a downstream interface ······························································287
Displaying and maintaining MLD configuration·······································································································287
MLD configuration examples ······································································································································288
Basic MLD functions configuration example·····································································································288
MLD SSM mapping configuration example ·····································································································291
MLD proxying configuration example···············································································································294
Troubleshooting MLD···················································································································································295
No member information on the receiver-side router························································································295
Inconsistent memberships on routers on the same subnet···············································································296
Configuring IPv6 PIM·············································································································································· 297
Understanding IPv6 PIM-DM ······························································································································297
Understanding IPv6 PIM-SM·······························································································································300
Understanding IPv6 BIDIR-PIM ···························································································································305
IPv6 administrative scoping································································································································308
Implementing an SSM model in IPv6 PIM·········································································································310
Configuring IPv6 PIM-DM···································································································································311
Protocols and standards ·····································································································································312
Configuration prerequisites································································································································312
Enabling IPv6 PIM-DM ········································································································································313
Enabling state-refresh capability························································································································313
Configuring state-refresh parameters ················································································································313
Configuring IPv6 PIM-DM graft retry period ····································································································314
Configuring IPv6 PIM-SM ············································································································································314
Prerequisites ·························································································································································314
Enabling IPv6 PIM-SM·········································································································································315
Configuring an RP ···············································································································································315
Configuring a BSR···············································································································································317
Configuring IPv6 administrative scoping··········································································································320
Configuring IPv6 multicast source registration·································································································322
Configuring SPT switchover································································································································323
Configuring IPv6 BIDIR-PIM·········································································································································323
IPv6 BIDIR-PIM configuration task list ················································································································323
Configuration prerequisites································································································································324
Enabling IPv6 PIM-SM·········································································································································324
Enabling IPv6 BIDIR-PIM ·····································································································································325
Configuring an RP ···············································································································································325
Configuring a BSR···············································································································································327
Configuring IPv6 administrative scoping··········································································································330
x
Configuring IPv6 PIM-SSM··········································································································································331
Configuration prerequisites································································································································331
Enabling IPv6 PIM-SM·········································································································································331
Configuring the IPv6 SSM group range ···········································································································332
Configuring IPv6 PIM common features············································································································332
Configuration prerequisites································································································································332
Configuring an IPv6 multicast data filter···········································································································333
Configuring a Hello message filter····················································································································333
Configuring IPv6 PIM Hello options ··················································································································334
Configuring the prune delay ······························································································································335
Configuring IPv6 PIM common timers···············································································································336
Configuring join/prune message sizes·············································································································337
Displaying and maintaining IPv6 PIM ·······················································································································337
IPv6 PIM configuration examples·······························································································································338
IPv6 PIM-DM configuration example·················································································································338
IPv6 PIM-SM non-scoped zone configuration example···················································································342
IPv6 PIM-SM admin-scope zone configuration example·················································································347
IPv6 BIDIR-PIM configuration example ··············································································································359
IPv6 PIM-SSM configuration example ···············································································································364
Troubleshooting IPv6 PIM configuration····················································································································367
Failure of building a multicast distribution tree correctly ················································································367
RPs unable to join SPT in IPv6 PIM-SM ·············································································································368
RPT establishment failure or source registration failure in IPv6 PIM-SM························································368
Configuring IPv6 MBGP configuration·················································································································· 370
Configuring IPv6 MBGP basic functions····················································································································370
Prerequisites ·························································································································································370
Configuring an IPv6 MBGP peer·······················································································································370
Configuring a preferred value for routes from a peer/peer group ·······························································371
Controlling route distribution and reception ·············································································································371
Prerequisites ·························································································································································371
Injecting a local IPv6 MBGP route·····················································································································371
Configuring IPv6 MBGP route redistribution ····································································································372
Configuring IPv6 MBGP route summarization ·································································································372
Advertising a default route to a peer or peer group ·······················································································372
Configuring outbound IPv6 MBGP route filtering ····························································································373
Configuring inbound IPv6 MBGP route filtering ······························································································373
Configuring IPv6 MBGP route dampening·······································································································374
Configuring IPv6 MBGP route attributes····················································································································374
Prerequisites ·························································································································································374
Configuring IPv6 MBGP route preferences ······································································································375
Configuring the default local preference ··········································································································375
Configuring the MED attribute···························································································································375
Configuring the NEXT_HOP attribute················································································································376
Configuring the AS_PATH attribute···················································································································376
Tuning and optimizing IPv6 MBGP networks············································································································377
Prerequisites ·························································································································································377
Configuring IPv6 MBGP soft reset ·····················································································································377
Enabling the IPv6 MBGP ORF capability ·········································································································378
Configuring the maximum number of equal-cost routes for load-balancing ·················································379
Configuring a large scale IPv6 MBGP network········································································································379
Prerequisites ·························································································································································379
Configuring an IPv6 MBGP peer group ···········································································································379
Configuring IPv6 MBGP community··················································································································380
Configuring an IPv6 MBGP route reflector·······································································································381
xi
Displaying and maintaining IPv6 MBGP···················································································································381
Resetting IPv6 MBGP connections ·····················································································································382
Clearing IPv6 MBGP information ······················································································································383
IPv6 MBGP configuration example ····························································································································383
Support and other resources ·································································································································· 387
Contacting HP ······························································································································································387
Subscription service ············································································································································387
Related information······················································································································································387
Documents····························································································································································387
Websites ······························································································································································387
Conventions ··································································································································································388
Index ········································································································································································ 390
1
Configuring IP multicast
This document focuses on the IP multicast technology and device operations. Unless otherwise stated, the
term multicast in this document refers to IP multicast.
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.
Comparing information transmission techniques
As an information transmission 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.
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
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
In Figure 1, assume that Hosts B, D, and 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 users need the information, the information source must send a
copy of the same information to each of these users. Sending many copies can place tremendous
pressure on the information source and the network bandwidth.
2
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 Hosts B, D, and E need the information. If the information is broadcast to the
subnet, Hosts A and C also receive it. In addition to information security issues, broadcasting to hosts that
do not need the information causes traffic flooding on the same subnet.
Broadcast is disadvantageous in transmitting data to specific hosts. Moreover, broadcast transmission is
a significant waste of network resources.
Multicast
Unicast and broadcast techniques cannot provide point-to-multipoint data transmissions with the minimum
network consumption. Multicast transmission can solve this problem. When some hosts on the network
need multicast information, the information sender, or multicast source, sends only one copy of the
information. Multicast distribution trees are built through multicast routing protocols, and the packets are
replicated only on nodes where the trees branch.
3
Figure 3 Multicast transmission
The multicast source sends only one copy of the information to a multicast group. In Figure 3, Hosts B, D,
and 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 Hosts B, D, and E.
The advantages of multicast over unicast and broadcast include:
•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 and does not significatly add to the usage of network resources.
•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, while multicast is not.
Multicast features
Multicast features include:
•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
manage multicast group memberships on stub subnets with attached group members. A multicast
router itself can be a multicast group member.
4
For a better understanding of the multicast concept, you can compare multicast transmission to the
transmission of TV programs.
Table 1 An analogy between TV transmission and multicast transmission
TV transmission Multicast transmission
A TV station transmits a TV program through a
channel.
A multicast source sends multicast data to a multicast
group.
A user tunes the TV set to the channel. A receiver joins the multicast group.
The user starts to watch the TV program
transmitted by the TV station via the channel.
The receiver starts to receive the multicast data that the
source is sending to the multicast group.
The user turns off the TV set or tunes to another
channel.
The receiver leaves the multicast group or joins another
group.
Multicast common notations
The following notations are commonly used in multicast transmission:
•(*, G)—An RPT or a multicast packet that any multicast source sends to multicast group G. The
asterisk represents any multicast source and the G represents a specific multicast group.
•(S, G)—An SPT or a multicast packet that multicast source S sends to multicast group G. The S
represents a specific multicast source and the G represents a specific multicast group.
For more information about the concepts RPT and SPT, sees “Configuring PIM”and “Configuring IPv6
PIM.”
Multicast advantages and applications
Advantages of multicast include:
•Enhanced efficiency—Reduces the processor load related to information source servers and network
devices.
•Optimal performance—Reduces redundant traffic.
•Distributed application—Enables point-to-multipoint applications using minimul network resources.
Applications of multicast include:
•Multimedia and streaming applications, such as web TV, web radio, and realtime 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
Multicast models, including ASM, SFM, and SSM, determine how receivers treat multicast sources.
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 determine the position of 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. In the SFM model, the upper layer software checks
the source address of received multicast packets and permits or denies multicast traffic from specific
sources. Therefore, receivers can receive the multicast data from only part of the multicast sources. To a
receiver, not all multicast sources are valid because they are filtered.
SSM model
Users are sometimes interested in the multicast data from only certain multicast sources. The SSM model
provides a transmission service that enables users to specify, at the client side, the multicast sources they
prefer.
The primary 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 is an end-to-end service with architecture that involves several key areas, including:
•Addressing mechanism—A multicast source sends information to a group of receivers through a
multicast address.
•Host registration—Receiver hosts can join and leave multicast groups dynamically. This mechanism
is the basis for management of group memberships.
•Multicast routing—A multicast distribution tree (a forwarding path tree for multicast data on the
network) is constructed for delivering multicast data from a multicast source to receivers.
•Multicast applications—A software system that supports multicast applications, such as video
conferencing, must be installed on multicast sources and receiver hosts. The TCP/IP stack must
support reception and transmission of multicast data.
6
Multicast addresses
Network-layer multicast addresses (multicast IP addresses) enable 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.
IPv4 multicast addresses
IANA assigned 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.
Group membership is dynamic (hosts can join or leave multicast groups at any time).
Glop is a mechanism for assigning multicast addresses between different ASs. For example, filling an AS
number into the middle two bytes of 233.0.0.0 provides 255 multicast addresses for that AS. For more
information, see RFC 2770.
Table 3 Table 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
224.0.0.12 DHCP server/relay agent
224.0.0.13 All PIM routers
7
Address Description
224.0.0.14 RSVP encapsulation
224.0.0.15 All CBT routers
224.0.0.16 Designated SBM
224.0.0.17 All SBMs
224.0.0.18 VRRP
IPv6 multicast addresses
Figure 4 IPv6 multicast format
Group ID (112 bits)
0xFF Flags Scope
0 7 11 15 31
Referring to Figure 4, the fields of an IPv6 multicast address indicate the following:
•0xFF—Most significant eight bits are 11111111, indicating that this address is an IPv6 multicast
address.
•Flags—Contains four bits.
Figure 5 Format of the Flags field
Table 4 Description of the Flags field bits
Bit Descri
p
tion
0 Reserved, set to 0.
R
•When set to 0, it indicates that this address is an IPv6 multicast address without an
embedded RP address.
•When set to 1, it indicates that this address is an IPv6 multicast address with an
embedded RP address (the P and T bits must also be set to 1).
P
•When set to 0, it indicates that this address is an IPv6 multicast address not based on a
unicast prefix.
•When set to 1, it indicates that this address is an IPv6 multicast address based on a
unicast prefix (the T bit must also be set to 1).
T
•When set to 0, it indicates that this address is an IPv6 multicast address
permanently-assigned by IANA.
•When set to 1, it indicates that this address is a transient, or dynamically assigned IPv6
multicast address.
•Scope—Contains four bits, which indicate the scope of the IPv6 internetwork for which the multicast
traffic is intended.
8
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 and uniquely identifies an IPv6 multicast group that is within the scope
defined by the Scope field.
Ethernet multicast MAC addresses
When a unicast IP packet is transmitted over Ethernet, the destination MAC address is the MAC address
of the receiver. When a multicast packet is transmitted over Ethernet, the destination address is a multicast
MAC address because the packet is directed to a group formed by a number of receivers, rather than to
one specific receiver.
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 remaining 23 bits are the least-significant 23 bits of a multicast IPv4 address.
Figure 6 IPv4-to-MAC address mapping
The most-significant four bits of a multicast IPv4 address are 1110, which indicates that this address is a
multicast address. Only 23 bits of the remaining 28 bits are mapped to a MAC address, so five bits of
the multicast IPv4 address are lost. As a result, 32 multicast IPv4 addresses map to the same IPv4
multicast MAC address. Therefore, in Layer 2 multicast forwarding, a device might receive some multicast
data destined for other IPv4 multicast groups. The upper layer must filter such redundant data.
9
IPv6 multicast MAC addresses
The most-significant 16 bits of an IPv6 multicast MAC address are 0x3333. The remaining 32 bits are the
least-significant 32 bits of a multicast IPv6 address.
Figure 7 An example of IPv6-to-MAC address mapping
Multicast protocols
Generally, Layer 3 multicast refers to IP multicast working at the network layer. The corresponding
multicast protocols are Layer 3 multicast protocols, which include IGMP/MLD, PIM/IPv6 PIM, MSDP, and
MBGP/IPv6 MBGP. Layer 2 multicast refers to IP multicast working at the data link layer. The
corresponding multicast protocols are Layer 2 multicast protocols, which include IGMP snooping/MLD
snooping, and multicast VLAN/IPv6 multicast VLAN.
IGMP snooping, IGMP, multicast VLAN, PIM, MSDP, and MBGP are for IPv4. MLD snooping, MLD, IPv6
multicast VLAN, IPv6 PIM, and IPv6 MBGP are for IPv6.
This section provides only general descriptions about applications and functions of the Layer 2 and Layer
3 multicast protocols in a network. For more information about these protocols, see related documents in
the IP Multicast Configuration Guide.
Layer 3 multicast protocols
Layer 3 multicast protocols include multicast group management protocols and multicast routing
protocols.
Figure 8 Positions of Layer 3 multicast protocols
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