HPE FlexFabric 12900E User manual

HPE FlexFabric 12900E Switch Series
IP Multicast Configuration Guide
Part number: 5200-1231b
Software version: Release 2606 and later
Document version: 6W101-20161201

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Contents
Multicast overview ············································································1
Introduction to multicast ················································································································ 1
Information transmission techniques ························································································· 1
Multicast features ·················································································································· 3
Common notations in multicast ································································································ 4
Multicast benefits and applications···························································································· 4
Multicast models ·························································································································· 4
IP multicast architecture ················································································································ 5
Multicast addresses ··············································································································· 5
Multicast protocols ················································································································· 8
Multicast packet forwarding mechanism ························································································· 10
Multicast support for VPNs ··········································································································· 11
Introduction to VPN instances ································································································ 11
Multicast application in VPNs ································································································· 12
Configuring IGMP snooping ······························································ 13
Overview ·································································································································· 13
IGMP snooping ports ··········································································································· 13
How IGMP snooping works ··································································································· 15
IGMP snooping proxying ······································································································· 16
Protocols and standards ······································································································· 17
IGMP snooping configuration task list ···························································································· 17
IGMP snooping configuration task list for VLANs ······································································· 17
IGMP configuration task list for VSIs ······················································································· 18
Configuring basic IGMP snooping features ····················································································· 18
Enabling IGMP snooping ······································································································ 19
Specifying an IGMP snooping version ····················································································· 19
Setting the maximum number of IGMP snooping forwarding entries ·············································· 20
Configuring static multicast MAC address entries ······································································ 21
Setting the IGMP last member query interval ············································································ 21
Configuring IGMP snooping port features ······················································································· 22
Setting aging timers for dynamic ports ····················································································· 22
Configuring static ports ········································································································· 23
Configuring a port as a simulated member host ········································································· 24
Enabling fast-leave processing ······························································································ 24
Disabling a port from becoming a dynamic router port ································································ 25
Enabling inner VLAN ID-based forwarding ··············································································· 25
Configuring the IGMP snooping querier ·························································································· 26
Configuration prerequisites···································································································· 26
Enabling the IGMP snooping querier ······················································································· 26
Configuring parameters for IGMP general queries and responses ················································ 27
Enabling IGMP snooping proxying ································································································· 27
Configuring parameters for IGMP messages ··················································································· 28
Configuration prerequisites···································································································· 28
Configuring source IP addresses for IGMP messages ································································ 28
Setting the 802.1p priority for IGMP messages ········································································· 30
Configuring IGMP snooping policies ······························································································ 30
Configuring a multicast group policy ························································································ 31
Enabling multicast source port filtering ···················································································· 31
Enabling dropping unknown multicast data ··············································································· 32
Enabling IGMP report suppression ························································································· 32
Setting the maximum number of multicast groups on a port ························································· 32
Enabling multicast group replacement ····················································································· 33
Enabling host tracking ·········································································································· 34
Displaying and maintaining IGMP snooping ···················································································· 34
IGMP snooping configuration examples ························································································· 36
Group policy and simulated joining configuration example(for VLANs) ··········································· 36

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Static port configuration example (for VLANs) ··········································································· 38
IGMP snooping querier configuration example (for VLANs) ························································· 40
IGMP snooping proxying configuration example (for VLANs) ······················································· 43
Troubleshooting IGMP snooping ··································································································· 44
Layer 2 multicast forwarding cannot function ············································································ 44
Multicast group policy does not work ······················································································· 45
Configuring PIM snooping ································································ 46
Overview ·································································································································· 46
Configuring PIM snooping ············································································································ 47
Displaying and maintaining PIM snooping ······················································································· 48
PIM snooping configuration example (for VLANs) ············································································· 48
Network requirements ·········································································································· 48
Configuration procedure ······································································································· 49
Verifying the configuration ····································································································· 51
Troubleshooting PIM snooping ····································································································· 52
PIM snooping does not work on a Layer 2 device ······································································ 52
Configuring multicast VLANs ···························································· 53
Overview ·································································································································· 53
Multicast VLAN configuration task list····························································································· 55
Configuring a sub-VLAN-based multicast VLAN ··············································································· 55
Configuration prerequisites···································································································· 55
Configuration restrictions and guidelines ·················································································· 55
Configuration procedure ······································································································· 55
Configuring a port-based multicast VLAN ······················································································· 56
Configuration prerequisites···································································································· 56
Configuring user port attributes ······························································································ 56
Assigning user ports to a multicast VLAN ················································································· 56
Setting the maximum number of multicast VLAN forwarding entries ····················································· 57
Displaying and maintaining multicast VLANs ··················································································· 57
Multicast VLAN configuration examples ·························································································· 58
Sub-VLAN-based multicast VLAN configuration example ···························································· 58
Port-based multicast VLAN configuration example ····································································· 61
Configuring multicast routing and forwarding ········································ 65
Overview ·································································································································· 65
RPF check mechanism ········································································································· 65
Static multicast routes ·········································································································· 67
Multicast forwarding across unicast subnets ············································································· 68
Configuration task list·················································································································· 69
Enabling IP multicast routing ········································································································ 69
Configuring multicast routing and forwarding ··················································································· 70
Configuring static multicast routes ·························································································· 70
Specifying the longest prefix match principle············································································· 70
Configuring multicast load splitting ·························································································· 71
Configuring a multicast forwarding boundary ············································································ 71
Setting the multicast hardware resource mode················································································· 71
Displaying and maintaining multicast routing and forwarding ······························································ 72
Configuration examples ··············································································································· 73
Changing an RPF route ········································································································ 73
Creating an RPF route ········································································································· 75
Troubleshooting multicast routing and forwarding ············································································· 77
Static multicast route failure··································································································· 77
Configuring IGMP ··········································································· 79
Overview ·································································································································· 79
IGMPv1 overview ················································································································ 79
IGMPv2 enhancements ········································································································ 80
IGMPv3 enhancements ········································································································ 81
IGMP SSM mapping ············································································································ 82
IGMP proxying ···················································································································· 83

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IGMP support for VPNs ········································································································ 84
Protocols and standards ······································································································· 84
IGMP configuration task list ·········································································································· 85
Configuring basic IGMP features ··································································································· 85
Enabling IGMP ··················································································································· 85
Specifying an IGMP version ·································································································· 86
Configuring a static group member ························································································· 86
Configuring a multicast group policy ························································································ 86
Adjusting IGMP performance ········································································································ 87
Configuring IGMP query and response parameters ···································································· 87
Enabling fast-leave processing ······························································································ 89
Configuring IGMP SSM mappings ································································································· 90
Configuration prerequisites···································································································· 90
Configuration procedure ······································································································· 90
Configuring IGMP proxying ·········································································································· 90
Configuration prerequisites···································································································· 90
Enabling IGMP proxying ······································································································· 90
Enabling multicast forwarding on a non-querier interface ···························································· 91
Configuring multicast load splitting on an IGMP proxy ································································ 91
Enabling IGMP NSR ··················································································································· 92
Displaying and maintaining IGMP ·································································································· 92
IGMP configuration examples ······································································································· 93
Basic IGMP features configuration example ············································································· 93
IGMP SSM mapping configuration example·············································································· 95
IGMP proxying configuration example ····················································································· 98
Troubleshooting IGMP ················································································································ 99
No membership information on the receiver-side router ······························································ 99
Inconsistent membership information on the routers on the same subnet ······································· 99
Configuring PIM ··········································································· 101
Overview ································································································································ 101
PIM-DM overview ·············································································································· 101
PIM-SM overview ·············································································································· 103
BIDIR-PIM overview ·········································································································· 109
Administrative scoping overview ··························································································· 112
PIM-SSM overview ············································································································ 114
Relationship among PIM protocols························································································ 115
PIM support for VPNs ········································································································ 116
Protocols and standards ····································································································· 116
Configuring PIM-DM ················································································································· 116
PIM-DM configuration task list ····························································································· 117
Configuration prerequisites·································································································· 117
Enabling PIM-DM ·············································································································· 117
Enabling the state refresh feature ························································································· 117
Configuring state refresh parameters ···················································································· 118
Configuring the PIM-DM graft retry timer ················································································ 118
Configuring PIM-SM ················································································································· 119
PIM-SM configuration task list ······························································································ 119
Configuration prerequisites·································································································· 119
Enabling PIM-SM ·············································································································· 119
Configuring an RP ············································································································· 120
Configuring a BSR ············································································································· 122
Configuring multicast source registration ················································································ 124
Configuring the switchover to SPT ························································································ 125
Configuring BIDIR-PIM ·············································································································· 125
BIDIR-PIM configuration task list ·························································································· 125
Configuration prerequisites·································································································· 126
Enabling BIDIR-PIM ··········································································································· 126
Configuring an RP ············································································································· 126
Configuring a BSR ············································································································· 128
Configuring PIM-SSM ··············································································································· 131
PIM-SSM configuration task list ···························································································· 131

iv
Configuration prerequisites·································································································· 131
Enabling PIM-SM ·············································································································· 131
Configuring the SSM group range ························································································· 131
Configuring common PIM features ······························································································ 132
Configuration task list ········································································································· 132
Configuration prerequisites·································································································· 132
Configuring a multicast source policy ···················································································· 132
Configuring a PIM hello policy ······························································································ 133
Configuring PIM hello message options ················································································· 133
Configuring common PIM timers ·························································································· 135
Setting the maximum size of a join or prune message ······························································ 136
Enabling BFD for PIM ········································································································ 136
Enabling PIM passive mode ································································································ 137
Enabling PIM NSR············································································································· 137
Enabling SNMP notifications for PIM ····················································································· 137
Setting a DSCP value for outgoing PIM messages ··································································· 138
Displaying and maintaining PIM ·································································································· 138
PIM configuration examples ······································································································· 139
PIM-DM configuration example ···························································································· 139
PIM-SM non-scoped zone configuration example ···································································· 142
PIM-SM admin-scoped zone configuration example ································································· 144
BIDIR-PIM configuration example ························································································· 149
PIM-SSM configuration example ·························································································· 153
Troubleshooting PIM················································································································· 156
A multicast distribution tree cannot be correctly built ································································ 156
Multicast data is abnormally terminated on an intermediate router ·············································· 157
An RP cannot join an SPT in PIM-SM ··················································································· 157
An RPT cannot be built or multicast source registration fails in PIM-SM ······································· 157
Configuring MSDP ········································································ 159
Overview ································································································································ 159
How MSDP works ············································································································· 159
MSDP support for VPNs ····································································································· 164
Protocols and standards ····································································································· 164
MSDP configuration task list ······································································································· 165
Configuring basic MSDP features ································································································ 165
Configuration prerequisites·································································································· 165
Enabling MSDP ················································································································ 165
Specifying an MSDP peer ··································································································· 166
Configuring a static RPF peer ······························································································ 166
Configuring an MSDP peering connection ····················································································· 166
Configuration prerequisites·································································································· 166
Configuring a description for an MSDP peer ··········································································· 167
Configuring an MSDP mesh group ························································································ 167
Controlling MSDP peering connections ·················································································· 167
Configuring SA message-related parameters ················································································ 168
Configuration prerequisites·································································································· 168
Enabling multicast data encapsulation in SA messages ···························································· 168
Configuring the originating RP of SA messages ······································································ 169
Configuring SA request messages ························································································ 169
Configuring SA message policies ························································································· 170
Configuring the SA cache mechanism ··················································································· 171
Enabling MSDP NSR ················································································································ 171
Displaying and maintaining MSDP ······························································································· 171
MSDP configuration examples ···································································································· 172
PIM-SM inter-domain multicast configuration ·········································································· 172
Inter-AS multicast configuration by leveraging static RPF peers ················································· 177
Anycast RP configuration ···································································································· 181
SA message filtering configuration ························································································ 185
Troubleshooting MSDP ············································································································· 188
MSDP peers stay in disabled state ······················································································· 189
No SA entries exist in the router's SA message cache ······························································ 189

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No exchange of locally registered (S, G) entries between RPs ··················································· 190
Configuring MLD snooping ····························································· 191
Overview ································································································································ 191
MLD snooping ports ··········································································································· 191
How MLD snooping works··································································································· 193
MLD snooping proxying ······································································································ 194
MLD snooping version ········································································································ 195
Protocols and standards ····································································································· 195
MLD snooping configuration task list ···························································································· 195
MLD snooping configuration task list for VLANs ······································································ 195
MLD snooping configuration task list for VSIs ········································································· 196
Configuring basic MLD snooping features ····················································································· 197
Enabling MLD snooping ······································································································ 197
Setting the maximum number of MLD snooping forwarding entries ············································· 198
Configuring static IPv6 multicast MAC address entries ····························································· 198
Setting the MLD last listener query interval ············································································· 199
Configuring MLD snooping port features ······················································································· 199
Setting aging timers for dynamic ports ··················································································· 200
Configuring static ports ······································································································· 201
Configuring a port as a simulated member host ······································································· 201
Enabling fast-leave processing ···························································································· 202
Disabling a port from becoming a dynamic router port ······························································ 202
Enabling inner VLAN ID-based forwarding ············································································· 203
Configuring the MLD snooping querier ························································································· 203
Configuration prerequisites·································································································· 203
Enabling the MLD snooping querier ······················································································ 203
Configuring parameters for MLD general queries and responses ················································ 204
Enabling MLD snooping proxying ································································································ 205
Configuring parameters for MLD messages ·················································································· 205
Configuration prerequisites·································································································· 205
Configuring source IPv6 addresses for MLD messages ···························································· 205
Setting the 802.1p priority for MLD messages ········································································· 207
Configuring MLD snooping policies ······························································································ 208
Configuring an IPv6 multicast group policy ············································································· 208
Enabling IPv6 multicast source port filtering············································································ 209
Enabling dropping unknown IPv6 multicast data ······································································ 209
Enabling MLD report suppression ························································································· 210
Setting the maximum number of IPv6 multicast groups on a port ················································ 210
Enabling IPv6 multicast group replacement ············································································ 211
Enabling host tracking ········································································································ 211
Displaying and maintaining MLD snooping ···················································································· 212
MLD snooping configuration examples ························································································· 214
IPv6 group policy and simulated joining configuration example (for VLANs) ·································· 214
Static port configuration example (for VLANs) ········································································· 216
MLD snooping querier configuration example (for VLANs) ························································· 218
MLD snooping proxying configuration example (for VLANs)······················································· 220
Troubleshooting MLD snooping ·································································································· 222
Layer 2 multicast forwarding cannot function ·········································································· 222
IPv6 multicast group policy does not work ·············································································· 223
Document conventions and icons ···················································· 224
Conventions ···························································································································· 224
Network topology icons ············································································································· 225
Support and other resources··························································· 226
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Index ························································································· 228

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

2
Broadcast
In broadcast transmission, the information source sends information to all hosts on the subnet, even
if some hosts do not need the information.
Figure 2 Broadcast transmission
In Figure 2, only Host B, Host D, and Host E need the information. If the information is broadcast to
the subnet, Host 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
Multicast provides point-to-multipoint data transmissions with the minimum network consumption.
When some hosts on the network need multicast information, the information sender, or multicast
source, sends only one copy of the information. Multicast distribution trees are built through multicast
routing protocols, and the packets are replicated only on nodes where the trees branch.
Source
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for all hosts
A network segment

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

4
Table 1 Comparing TV program transmission and multicast transmission
TV program transmission
Multicast transmission
A TV station transmits a TV program through a
channel.
A multicast source sends multicast data to a multicast
group.
A user tunes the TV set to the channel. A receiver joins the multicast group.
The user starts to watch the TV program
transmitted by the TV station on the channel.
The receiver starts to receive the multicast data sent by
the source to the multicast group.
The user turns off the TV set or tunes to another
channel.
The receiver leaves the multicast group or joins another
group.
Common notations in multicast
The following notations are commonly used in multicast transmission:
•
(*, G)—Rendezvous point tree (RPT), or a multicast packet that any multicast source sends to
multicast group G. The asterisk (*) represents any multicast source, and "G" represents a
specific multicast group.
•
(S, G)—Shortest path tree (SPT), or a multicast packet that multicast source "S" sends to
multicast group "G." "S" represents a specific multicast source, and "G" represents a specific
multicast group.
For more information about the concepts RPT and SPT, see "Configuring PIM."
Multicast benefits and applications
Multicast benefits
•
Enhanced efficiency—Reduces the processor load of information source servers and network
devices.
•
Optimal performance—Reduces redundant traffic.
•
Distributed application—Enables point-to-multipoint applications at the price of minimum
network resources.
Multicast applications
•
Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audio
conferencing
•
Communication for training and cooperative operations, such as distance learning and
telemedicine
•
Data warehouse and financial applications (stock quotes)
•
Any other point-to-multipoint application for data distribution
Multicast models
Based on how the receivers treat the multicast sources, the multicast models include any-source
multicast (ASM), source-filtered multicast (SFM), and source-specific multicast (SSM).
ASM model
In the ASM model, any multicast sources can send information to a multicast group. Receivers can
join a multicast group and get multicast information addressed to that multicast group from any
multicast sources. In this model, receivers do not know the positions of the multicast sources in
advance.

5
SFM model
The SFM model is derived from the ASM model. To a multicast source, the two models appear to
have the same multicast membership architecture.
The SFM model functionally extends the ASM model. The upper-layer software checks the source
address of received multicast packets and permits or denies multicast traffic from specific sources.
The receivers obtain the multicast data from only part of the multicast sources. To a receiver,
multicast sources are not all valid, but are filtered.
SSM model
The SSM model provides a transmission service that enables multicast receivers to specify the
multicast sources in which they are interested.
In the SSM model, receivers have already determined the locations of the multicast sources. This is
the main difference between the SSM model and the ASM model. In addition, the SSM model uses a
different multicast address range than the ASM/SFM model. Dedicated multicast forwarding paths
are established between receivers and the specified multicast sources.
IP multicast architecture
IP multicast addresses the following issues:
•
Where should the multicast source transmit information to? (Multicast addressing.)
•
What receivers exist on the network? (Host registration.)
•
Where is the multicast source that will provide data to the receivers? (Multicast source
discovery.)
•
How is the information transmitted to the receivers? (Multicast routing.)
IP multicast is an end-to-end service. The multicast architecture involves the following parts:
•
Addressing mechanism—A multicast source sends information to a group of receivers
through a multicast address.
•
Host registration—Receiver hosts can join and leave multicast groups dynamically. This
mechanism is the basis for management of group memberships.
•
Multicast routing—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.
Multicast addresses
IP multicast addresses
•
IPv4 multicast addresses:
IANA assigned the Class D address block (224.0.0.0 to 239.255.255.255) to IPv4 multicast.
Table 2 Class D IP address blocks and description
Address block
Description
224.0.0.0 to 224.0.0.255
Reserved permanent group addresses. The IP address 224.0.0.0
is reserved. Other IP addresses can be used by routing protocols
and for topology searching, protocol maintenance, and so on.
Table 3 lists common
permanent 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.

6
Address block
Description
224.0.1.0 to 238.255.255.255
Globally scoped group addresses. This block includes the
following types of designated group addresses:
• 232.0.0.0/8—SSM group addresses.
• 233.0.0.0/8—Glop group addresses.
239.0.0.0 to 239.255.255.255
Administratively scoped multicast addresses. These addresses
are considered locally unique rather than globally unique. You can
reuse them in domains administered by different organizations
without causing conflicts. For more information, see RFC 2365.
NOTE:
Glop is a mechanism for assigning multicast addresses between different ASs. By filli
ng an AS
number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS. For more
information, see RFC 2770.
Table 3 Common permanent multicast group addresses
Address
Description
224.0.0.1 All systems on this subnet, including hosts and routers.
224.0.0.2 All multicast routers on this subnet.
224.0.0.3 Unassigned.
224.0.0.4 DVMRP routers.
224.0.0.5 OSPF routers.
224.0.0.6 OSPF designated routers and backup designated routers.
224.0.0.7 Shared Tree (ST) routers.
224.0.0.8 ST hosts.
224.0.0.9 RIPv2 routers.
224.0.0.11 Mobile agents.
224.0.0.12 DHCP server/relay agent.
224.0.0.13 All Protocol Independent Multicast (PIM) routers.
224.0.0.14 RSVP encapsulation.
224.0.0.15 All Core-Based Tree (CBT) routers.
224.0.0.16 Designated SBM.
224.0.0.17 All SBMs.
224.0.0.18 VRRP.
•
IPv6 multicast addresses:
Figure 4 IPv6 multicast format
Group ID (112 bits)
0xFF Flags Scope
0 7 11 15 31

7
The following describes the fields of an IPv6 multicast address:
 0xFF—The most significant eight bits are 11111111.
 Flags—The Flags field contains four bits.
Figure 5 Flags field format
Table 4 Flags field description
Bit
Description
0 Reserved, set to 0.
R
• When set to 0, this address is an IPv6 multicast address
without an embedded RP address.
• When set to 1, this address is an IPv6 multicast address with
an embedded RP address. (The P and T bits must also be set
to 1.)
P
• When set to 0, this address is an IPv6 multicast address not
based on a unicast prefix.
• When set to 1, this address is an IPv6 multicast address
based on a unicast prefix. (The T bit must also be set to 1.)
T
• When set to 0, this address is an IPv6 multicast address
permanently-assigned by IANA.
• When set to 1
, this address is a transient or dynamically
assigned IPv6 multicast address.
 Scope—The Scope field contains four bits, which represent the scope of the IPv6
internetwork for which the multicast traffic is intended.
Table 5 Values of the Scope field
Value
Meaning
0, F Reserved.
1 Interface-local scope.
2 Link-local scope.
3 Subnet-local scope.
4 Admin-local scope.
5 Site-local scope.
6, 7, 9 through D Unassigned.
8 Organization-local scope.
E Global scope.
 Group ID—The Group ID field contains 112 bits. It uniquely identifies an IPv6 multicast
group in the scope that the Scope field defines.
Ethernet multicast MAC addresses
•
IPv4 multicast MAC addresses:
As defined by IANA, the most significant 24 bits of an IPv4 multicast MAC address are
0x01005E. Bit 25 is 0, and the other 23 bits are the least significant 23 bits of an IPv4 multicast
address.
0RPT

8
Figure 6 IPv4-to-MAC address mapping
The most significant four bits of an IPv4 multicast address are fixed at 1110. In an IPv4-to-MAC
address mapping, five bits of the IPv4 multicast address are lost. As a result, 32 IPv4 multicast
addresses are mapped to the same IPv4 multicast MAC address. A device might receive
unwanted multicast data at Layer 2 processing, which needs to be filtered by the upper layer.
•
IPv6 multicast MAC addresses:
As defined by IANA, the most significant 16 bits of an IPv6 multicast MAC address are 0x3333.
The least significant 32 bits are mapped from the least significant 32 bits of an IPv6 multicast
address. Therefore, the problem of duplicate IPv6-to-MAC address mapping also arises like
IPv4-to-MAC address mapping.
Figure 7 IPv6-to-MAC address mapping
IMPORTAN
T:
Because of the duplicate mapping from
multicast IP address to multicast MAC address
, the device
might
inadvertently send multicast protocol packets as multicast data in Layer 2 forwarding. To avoid
this, do not use the IP multicast addresses that are ma
pped to multicast MAC addresses
0100-5E00-00xx and 3333-0000-00xx (where "x" represents any hexadecimal number from 0 to F).
Multicast protocols
Multicast protocols include the following categories:
•
Layer 3 and Layer 2 multicast protocols:
 Layer 3 multicast refers to IP multicast operating at the network layer.
Layer 3 multicast protocols—IGMP, MLD, PIM, IPv6 PIM, MSDP, MBGP, and IPv6
MBGP.
 Layer 2 multicast refers to IP multicast operating at the data link layer.
Layer 2 multicast protocols—IGMP snooping, MLD snooping, PIM snooping, IPv6 PIM
snooping, multicast VLAN, and IPv6 multicast VLAN.
XXXX X
XXXX XXXX XXXX XXXX XXXX XXXX
1110 XXXX
0XXX XXXX XXXX XXXX XXXX XXXX
0000 0001 0000 0000 0101 1110
32-bit IPv4 address
48-bit MAC address
5 bits lost
25-bit MAC address prefix
…23 bits
mapped
…
FF1 E 0000 0000 0000 0000 0000 F30E0101
0101aF 30E
48-bit MAC address 3333
32 bits
mapped
128-bit IPv6 address
… …
16-bit MAC
address prefix

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

10
For the SSM model, multicast routes are not divided into intra-domain routes and inter-domain
routes. Because receivers know the positions of the multicast sources, channels established
through PIM-SM are sufficient for the transport of multicast information.
Layer 2 multicast protocols
In Figure 9, Layer 2 multicast protocols include IGMP snooping, MLD snooping, PIM snooping, IPv6
PIM snooping, multicast VLAN, and IPv6 multicast VLAN.
Figure 9 Positions of Layer 2 multicast protocols
•
IGMP snooping and MLD snooping:
IGMP snooping and MLD snooping are multicast constraining mechanisms that run on Layer 2
devices. They manage and control multicast groups by monitoring and analyzing IGMP or MLD
messages exchanged between the hosts and Layer 3 multicast devices. This effectively
controls the flooding of multicast data in Layer 2 networks.
•
PIM snooping and IPv6 PIM snooping:
PIM snooping and IPv6 PIM snooping run on Layer 2 devices. They work with IGMP snooping
or MLD snooping to analyze received PIM messages. Then, they add the ports that are
interested in specific multicast data to a PIM snooping routing entry or IPv6 PIM snooping
routing entry. In this way, multicast data can be forwarded to only the ports that are interested in
the data.
•
Multicast VLAN and IPv6 multicast VLAN:
Multicast VLAN or IPv6 multicast VLAN runs on a Layer 2 device in a multicast network where
multicast receivers for the same group exist in different VLANs. With these protocols, the Layer
3 multicast device sends only one copy of multicast to the multicast VLAN or IPv6 multicast
VLAN on the Layer 2 device. This method avoids waste of network bandwidth and extra burden
on the Layer 3 device.
Multicast packet forwarding mechanism
In a multicast model, receiver hosts of a multicast group are usually located at different areas on the
network. They are identified by the same multicast group address. To deliver multicast packets to
these receivers, a multicast source encapsulates the multicast data in an IP packet with the multicast
group address as the destination address. Multicast routers on the forwarding paths forward
multicast packets that an incoming interface receives through multiple outgoing interfaces.
Compared to a unicast model, a multicast model is more complex in the following aspects:
IPv4/IPv6 multicast packets (S1, G1) IPv4/IPv6 multicast packets (S2, G2)
Source 1
Source 2
Receiver
IGMP Snooping
/MLD Snooping
Receiver Receiver
Multicast VLAN
/IPv6 Multicast VLAN
PIM Snooping
/IPv6 PIM Snooping

11
•
To ensure multicast packet transmission on the network, different routing tables are used to
guide multicast forwarding. These routing tables include unicast routing tables, routing tables
for multicast (for example, the MBGP routing table), and static multicast routing tables.
•
To process the same multicast information from different peers received on different interfaces,
the multicast device performs an RPF check on each multicast packet. The RPF check result
determines whether the packet will be forwarded or discarded. The RPF check mechanism is
the basis for most multicast routing protocols to implement multicast forwarding.
For more information about the RPF mechanism, see "Configuring multicast routing and
forwarding."
Multicast support for VPNs
Multicast support for VPNs refers to multicast applied in VPNs.
Introduction to VPN instances
VPNs are isolated from one another and from the public network. As shown in Figure 10, VPN A and
VPN B separately access the public network through PE devices.
Figure 10 VPN networking diagram
•
The P device belongs to the public network. The CE devices belong to their respective VPNs.
Each CE device serves its own VPN and maintains only one set of forwarding mechanisms.
•
The PE devices connect to the public network and the VPNs. Each PE device must strictly
distinguish the information for different networks, and maintain a separate forwarding
mechanism for each network. On a PE device, a set of software and hardware that serve the
same network forms an instance. Multiple instances can exist on the same PE device, and an
instance can reside on different PE devices. On a PE device, the instance for the public network
is called the public network instance, and those for VPNs are called VPN instances.
VPN A
VPN A
VPN A
VPN BVPN B
Public network
P
PE 1
PE 2
PE 3
CE b3
CE a2
CE a3
CE b1
CE a1
CE b2

12
Multicast application in VPNs
A PE device that supports multicast for VPNs performs the following operations:
•
Maintains an independent set of multicast forwarding mechanisms for each VPN, including the
multicast protocols, PIM neighbor information, and multicast routing table. In a VPN, the device
forwards multicast data based on the forwarding table or routing table for that VPN.
•
Implements the isolation between different VPNs.
•
Implements information exchange and data conversion between the public network and VPN
instances.
For example, as shown in Figure 10, a multicast source in VPN A sends multicast data to a multicast
group. Only receivers that belong to both the multicast group and VPN A can receive the multicast
data. The multicast data is multicast both in VPN A and on the public network.