H3C S3100-52P User manual

Operation Manual – Multicast
H3C S3100-52P Ethernet Switch Table of Contents
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Table of Contents
Chapter 1 Multicast Overview ......................................................................................................1-1
1.1 Multicast Overview.............................................................................................................1-1
1.1.1 Information Transmission in the Unicast Mode.......................................................1-1
1.1.2 Information Transmission in the Broadcast Mode...................................................1-2
1.1.3 Information Transmission in the Multicast Mode.....................................................1-3
1.1.4 Roles in Multicast....................................................................................................1-4
1.1.5 Advantages and Applications of Multicast ..............................................................1-5
1.2 Multicast Models................................................................................................................1-6
1.3 Multicast Architecture ........................................................................................................1-7
1.3.1 Multicast Protocols................................................................................................1-10
1.4 Multicast Packet Forwarding Mechanism........................................................................1-12
1.4.1 Implementation of the RPF Mechanism................................................................1-13
1.4.2 RPF Check............................................................................................................ 1-13
Chapter 2 Common Multicast Configuration..............................................................................2-1
2.1 Common Multicast Configuration.......................................................................................2-1
2.1.1 Configuring Suppression on the Multicast Source Port ..........................................2-1
2.1.2 Configuring a Multicast MAC Address Entry...........................................................2-2
2.1.3 Configuring Dropping Unknown Multicast Packets.................................................2-3
2.2 Displaying Common Multicast Configuration.....................................................................2-4
Chapter 3 IGMP Snooping Configuration ...................................................................................3-1
3.1 IGMP Snooping Overview .................................................................................................3-1
3.1.1 Principle of IGMP Snooping....................................................................................3-1
3.1.2 Basic Concepts in IGMP Snooping.........................................................................3-2
3.1.3 Work Mechanism of IGMP Snooping......................................................................3-3
3.2 IGMP Snooping Configuration Task List ...........................................................................3-5
3.2.1 Enabling IGMP Snooping........................................................................................3-6
3.2.2 Configuring the Version of IGMP Snooping............................................................3-6
3.2.3 Configuring Timers..................................................................................................3-7
3.2.4 Configuring Fast Leave Processing........................................................................3-8
3.2.5 Configuring a Multicast Group Filter........................................................................3-9
3.2.6 Configuring the Maximum Number of Multicast Groups on a Port .......................3-10
3.2.7 Configuring IGMP Snooping Querier .................................................................... 3-11
3.2.8 Suppressing Flooding of Unknown Multicast Traffic in a VLAN............................3-12
3.2.9 Configuring Static Member Port for a Multicast Group .........................................3-13
3.2.10 Configuring a Static Router Port ......................................................................... 3-14
3.2.11 Configuring a Port as a Simulated Group Member.............................................3-14
3.2.12 Configuring a VLAN Tag for Query Messages.................................................... 3-16

Operation Manual – Multicast
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3.2.13 Configuring Multicast VLAN................................................................................3-16
3.3 Displaying and Maintaining IGMP Snooping...................................................................3-18
3.4 IGMP Snooping Configuration Examples........................................................................3-19
3.4.1 Configuring IGMP Snooping .................................................................................3-19
3.4.2 Configuring Multicast VLAN..................................................................................3-21
3.5 Troubleshooting IGMP Snooping.....................................................................................3-24

Operation Manual – Multicast
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Chapter 1 Multicast Overview
Note:
In this manual, the term “router” refers to a router in the generic sense and a Layer 3
Ethernet switch running an IP multicast protocol.
zIGMPv3 Snooping features. Refer to Configuring the Version of IGMP Snooping
and Configuring a Port as a Simulated Group Member
zSuppressing Flooding of Unknown Multicast Traffic in a VLAN
zConfiguring Static Member Port for a Multicast Group
zConfiguring a Static Router Port
zConfiguring a VLAN Tag for Query Messages
1.1 Multicast Overview
With the development of the Internet, more and more interaction services such as data,
voice, and video services are running on the networks. In addition, highly bandwidth-
and time-critical services, such as e-commerce, Web conference, online auction, video
on demand (VoD), and tele-education have come into being. These services have
higher requirements for information security, legal use of paid services, and network
bandwidth.
In the network, packets are sent in three modes: unicast, broadcast and multicast. The
following sections describe and compare data interaction processes in unicast,
broadcast, and multicast.
1.1.1 Information Transmission in the Unicast Mode
In unicast, the system establishes a separate data transmission channel for each user
requiring this information, and sends a separate copy of the information to the user, as
shown in Figure 1-1:

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Source
Server
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
Figure 1-1 Information transmission in the unicast mode
Assume that Hosts B, D and E need this information. The source server establishes
transmission channels for the devices of these users respectively. As the transmitted
traffic over the network is in direct proportion to the number of users that receive this
information, when a large number of users need this information, the server must send
many pieces of information with the same content to the users. Therefore, the limited
bandwidth becomes the bottleneck in information transmission. This shows that unicast
is not good for the transmission of a great deal of information.
1.1.2 Information Transmission in the Broadcast Mode
When you adopt broadcast, the system transmits information to all users on a network.
Any user on the network can receive the information, no matter the information is
needed or not. Figure 1-2 shows information transmission in broadcast mode.

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Source
Server
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for all the network
Figure 1-2 Information transmission in the broadcast mode
Assume that Hosts B, D, and E need the information. The source server broadcasts this
information through routers, and Hosts A and C on the network also receive this
information.
As we can see from the information transmission process, the security and legal use of
paid service cannot be guaranteed. In addition, when only a small number of users on
the same network need the information, the utilization ratio of the network resources is
very low and the bandwidth resources are greatly wasted.
Therefore, broadcast is disadvantageous in transmitting data to specific users;
moreover, broadcast occupies large bandwidth.
1.1.3 Information Transmission in the Multicast Mode
As described in the previous sections, unicast is suitable for networks with sparsely
distributed users, whereas broadcast is suitable for networks with densely distributed
users. When the number of users requiring information is not certain, unicast and
broadcast deliver a low efficiency.
Multicast solves this problem. When some users on a network require specified
information, the multicast information sender (namely, the multicast source) sends the
information only once. With multicast distribution trees established for multicast data
packets through multicast routing protocols, the packets are duplicated and distributed
at the nearest nodes, as shown in Figure 1-3:

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Source
Server
Receiver
Receiver
Receiver
Host A
Host B
Host C
Host D
Host E
Packets for the multicast group
Figure 1-3 Information transmission in the multicast mode
Assume that Hosts B, D and E need the information. To transmit the information to the
right users, it is necessary to group Hosts B, D and E into a receiver set. The routers on
the network duplicate and distribute the information based on the distribution of the
receivers in this set. Finally, the information is correctly delivered to Hosts B, D, and E.
The advantages of multicast over unicast are as follows:
zNo matter how many receivers exist, there is only one copy of the same multicast
data flow on each link.
zWith the multicast mode used to transmit information, an increase of the number of
users does not add to the network burden remarkably.
The advantages of multicast over broadcast are as follows:
zA multicast data flow can be sent only to the receiver that requires the data.
zMulticast brings no waste of network resources and makes proper use of
bandwidth.
1.1.4 Roles in Multicast
The following roles are involved in multicast transmission:
zAn information sender is referred to as a multicast source (“Source” in Figure 1-3).
zEach receiver is a multicast group member (“Receiver” in Figure 1-3).
zAll receivers interested in the same information form a multicast group. Multicast
groups are not subject to geographic restrictions.

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zA router that supports Layer 3 multicast is called multicast router or Layer 3
multicast device. In addition to providing multicast routing, a multicast router can
also manage multicast group members.
For a better understanding of the multicast concept, you can assimilate multicast
transmission to the transmission of TV programs, as shown in Table 1-1.
Table 1-1 An analogy between TV transmission and multicast transmission
Step TV transmission Multicast transmission
1 A TV station transmits a TV
program through a television
channel.
A multicast source sends multicast
data to a multicast group.
2 A user tunes the TV set to the
channel. A receiver joins the multicast group.
3 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 sends
to the multicast group.
4 The user turns off the TV set. The receiver leaves the multicast
group.
Note:
zA multicast source does not necessarily belong to a multicast group. Namely, a
multicast source is not necessarily a multicast data receiver.
zA 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.
1.1.5 Advantages and Applications of Multicast
I. Advantages of multicast
Advantages of multicast include:
zEnhanced efficiency: Multicast decreases network traffic and reduces server load
and CPU load.
zOptimal performance: Multicast reduces redundant traffic.
zDistributive application: Multicast makes multiple-point application possible.
II. Application of multicast
The multicast technology effectively addresses the issue of point-to-multipoint data
transmission. By enabling high-efficiency point-to-multipoint data transmission, over an
IP network, multicast greatly saves network bandwidth and reduces network load.

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Multicast provides the following applications:
zApplications of multimedia and flow media, such as Web TV, Web radio, and
real-time video/audio conferencing.
zCommunication for training and cooperative operations, such as remote
education.
zDatabase and financial applications (stock), and so on.
zAny point-to-multiple-point data application.
1.2 Multicast Models
Based on the multicast source processing modes, there are three multicast models:
zAny-source multicast (ASM)
zSource-filtered multicast (SFM)
zSource-specific multicast (SSM)
I. ASM model
In the ASM model, any sender can become a multicast source and send information to
a multicast group; numbers of receivers can join a multicast group identified by a group
address and obtain multicast information addressed to that multicast group. In this
model, receivers are not aware of the position of a multicast source in advance.
However, they can join or leave the multicast group at any time.
II. SFM model
The SFM model is derived from the ASM model. From the view of a sender, the two
models have the same multicast group membership architecture.
Functionally, the SFM model is an extension of the ASM model. In the SFM model, the
upper layer software checks the source address of received multicast packets so as to
permit or deny multicast traffic from specific sources. Therefore, receivers can receive
the multicast data from only part of the multicast sources. From the view of a receiver,
multicast sources are not all valid: they are filtered.
III. SSM model
In the practical life, users may be interested in the multicast data from only certain
multicast sources. The SSM modelprovides a transmission service that allows users to
specify the multicast sources they are interested in at the client side.
The radical difference between the SSM model and the ASM model is that in the SSM
model, receivers already know the locations of the multicast sources by some means.
In addition, the SSM model uses a multicast address range that is different from that of
the ASM model, and dedicated multicast forwarding paths are established between
receivers and the specified multicast sources.

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1.3 Multicast Architecture
The purpose of IP multicast is to transmit information from a multicast source to
receivers in the multicast mode and to satisfy information requirements of receivers.
You should be concerned about:
zHost registration: What receivers reside on the network?
zTechnologies of discovering a multicast source: Which multicast source should
the receivers receive information from?
zMulticast addressing mechanism: Where should the multicast source transports
information?
zMulticast routing: How is information transported?
IP multicast is a kind of peer-to-peer service. Based on the protocol layer sequence
from bottom to top, the multicast mechanism contains addressing mechanism, host
registration, multicast routing, and multicast application:
zAddressing mechanism: Information is sent from a multicast source to a group of
receivers through multicast addresses.
zHost registration: A receiving host joins and leaves a multicast group dynamically
using the membership registration mechanism.
zMulticast routing: A router or switch transports packets from a multicast source to
receivers by building a multicast distribution tree with multicast routes.
zMulticast application: A multicast source must support multicast applications, such
as video conferencing. The TCP/IP protocol suite must support the function of
sending and receiving multicast information.
Multicast Address
As receivers are multiple hosts in a multicast group, you should be concerned about the
following questions:
zWhat destination should the information source send the information to in the
multicast mode?
zHow to select the destination address?
These questions are about multicast addressing. To enable the communication
between the information source and members of a multicast group (a group of
information receivers), network-layer multicast addresses, namely, IP multicast
addresses must be provided. In addition, a technology must be available to map IP
multicast addresses to link-layer MAC multicast addresses. The following sections
describe these two types of multicast addresses:
I. IP multicast address
Internet Assigned Numbers Authority (IANA) categorizes IP addresses into five classes:
A, B, C, D, and E. Unicast packets use IP addresses of Class A, B, and C based on
network scales. Class D IP addresses are used as destination addresses of multicast

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packets. Class D address must not appear in the IP address field of a source IP
address of IP packets. Class E IP addresses are reserved for future use.
In unicast data transport, a data packet is transported hop by hop from the source
address to the destinationaddress. In an IP multicast environment, there are a group of
destination addresses (called group address), rather than one address. All the
receivers join a group. Once they join the group, the data sent to this group of
addresses starts to be transported to the receivers. All the members in this group can
receive the data packets. This group is a multicast group.
A multicast group has the following characteristics:
zThe membership of a group is dynamic. A host can join and leave a multicast
group at any time.
zA multicast group can be either permanent or temporary.
zA multicast group whose addresses are assigned by IANA is a permanent
multicast group. It is also called reserved multicast group.
Note that:
zThe IP addresses of a permanent multicast group keep unchanged, while the
members of the group can be changed.
zThere can be any number of, or even zero, members in a permanent multicast
group.
zThose IP multicast addresses not assigned to permanent multicast groups can be
used by temporary multicast groups.
Class D IP addresses range from 224.0.0.0 to 239.255.255.255. For details, see Table
1-2.
Table 1-2 Range and description of Class D IP addresses
Class D address range Description
224.0.0.0 to 224.0.0.255
Reserved multicast addresses (IP addresses for
permanent multicast groups). The IP address
224.0.0.0 is reserved. Other IP addresses can be
used by routing protocols.
224.0.1.0 to 231.255.255.255
233.0.0.0 to 238.255.255.255
Available any-source multicast (ASM) multicast
addresses (IP addresses for temporary groups).
They are valid for the entire network.
232.0.0.0 to 232.255.255.255 Available source-specific multicast (SSM)
multicast group addresses.
239.0.0.0 to 239.255.255.255 Administratively scoped multicast addresses,
which are for specific local use only.
As specified by IANA, the IP addresses ranging from 224.0.0.0 to 224.0.0.255 are
reserved for network protocols on local networks. The following table lists commonly
used reserved IP multicast addresses: