H3C S9500 Series Operating instructions

Brand: H3C

Model: S9500 Series

Category: Network switches

Type: Operating instructions

Operation Manual – IGMP Snooping

H3C S9500 Series Routing Switches Table of Contents

Table of Contents

Chapter 1 IGMP Snooping Configuration ...................................................................................1-1

1.1 IGMP Snooping Overview .................................................................................................1-1

1.1.1 Principle of IGMP Snooping....................................................................................1-1

1.1.2 Basic Concepts in IGMP Snooping.........................................................................1-2

1.1.3 Work Mechanism of IGMP Snooping......................................................................1-4

1.1.4 Processing of Multicast Protocol Messages ...........................................................1-6

1.1.5 Protocols and Standards.........................................................................................1-7

1.2 IGMP Snooping Configuration Task List ...........................................................................1-7

1.3 Configuring Basic Functions of IGMP Snooping ...............................................................1-8

1.3.1 Configuration Prerequisites.....................................................................................1-8

1.3.2 Enabling IGMP Snooping........................................................................................1-8

1.3.3 Configuring the Version of IGMP Snooping............................................................1-9

1.3.4 Configuring the Function of Dropping Unknown Multicast Data.............................1-9

1.4 Configuring IGMP Snooping Port Functions....................................................................1-10

1.4.1 Configuration Prerequisites...................................................................................1-10

1.4.2 Configuring Static Ports ........................................................................................1-10

1.4.3 Configuring Simulated Joining ..............................................................................1-11

1.4.4 Configuring Fast Leave Processing......................................................................1-12

1.4.5 Configuring Aging Timers for Dynamic Ports........................................................1-13

1.5 Configuring IGMP-Related Functions..............................................................................1-14

1.5.1 Configuration Prerequisites...................................................................................1-14

1.5.2 Enabling IGMP Snooping Querier.........................................................................1-15

1.5.3 Configuring IGMP Queries and Responses..........................................................1-15

1.5.4 Configuring Source IP Address of IGMP Queries.................................................1-17

1.5.5 Configuring IGMP Report Suppression.................................................................1-18

1.6 Configuring a Multicast Group Policy...............................................................................1-18

1.6.1 Configuration Prerequisites...................................................................................1-18

1.6.2 Configuring a Multicast Group Filter......................................................................1-18

1.6.3 Configuring Maximum Multicast Groups that Can Be Joined on a Port................1-19

1.6.4 Configuring Multicast Group Replacement ...........................................................1-20

1.7 Displaying and Maintaining IGMP Snooping...................................................................1-21

1.8 IGMP Snooping Configuration Examples........................................................................1-22

1.8.1 Configuring Simulated Joining ..............................................................................1-22

1.8.2 IGMP Snooping Querier Configuration.................................................................1-24

1.8.3 Static Router Port Configuration ...........................................................................1-26

1.9 Troubleshooting IGMP Snooping Configuration..............................................................1-28

1.9.1 Switch Fails in Layer 2 Multicast Forwarding........................................................1-28

1.9.2 Configured Multicast Group Policy Fails to Take Effect........................................1-29

Operation Manual – IGMP Snooping

H3C S9500 Series Routing Switches Table of Contents

Operation Manual – IGMP Snooping

H3C S9500 Series Routing Switches Chapter 1 IGMP Snooping Configuration

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Chapter 1 IGMP Snooping Configuration

When configuration IGMP Snooping, go to the following sections for information you

are interested in:

z IGMP Snooping Overview

z Configuring Basic Functions of IGMP Snooping

z Configuring IGMP Snooping Port Functions

z Configuring IGMP-Related Functions

z Configuring a Multicast Group Policy

z Displaying and Maintaining IGMP Snooping

z IGMP Snooping Configuration Examples

z Troubleshooting IGMP Snooping Configuration

 Note:

For details about IGMP and PIM, refer to IGMP Configuration and PIM Configuration in

the IP Multicast Volume.

1.1 IGMP Snooping Overview

Internet Group Management Protocol Snooping (IGMP Snooping) is a multicast

constraining mechanism that runs on Layer 2 devices to manage and control multicast

groups.

1.1.1 Principle of IGMP Snooping

By analyzing received IGMP messages, a switch (Layer 2 device) running IGMP

Snooping establishes mappings between ports and multicast MAC addresses and

forwards multicast data based on these mappings.

As shown in

Figure 1-1, when IGMP Snooping is not running on the switch, multicast

packets are broadcast to all devices at Layer 2. When IGMP Snooping is running on the

switch, multicast packets for known multicast groups are multicast to the receivers,

rather than broadcast to all hosts, at Layer 2.

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Multicast packet transmission

without IGMP Snooping

Source

Multicast router

Host A

Receiver

Host B

Host C

Receiver

Multicast packets

Layer 2 switch

Multicast packet transmission

when IGMP Snooping runs

Source

Multicast router

Host A

Receiver

Host B

Host C

Receiver

Layer 2 switch

Figure 1-1 Before and after IGMP Snooping is enabled on Layer 2 device

1.1.2 Basic Concepts in IGMP Snooping

I. IGMP Snooping related ports

As shown in Figure 1-2, Router A connects to the multicast source, IGMP Snooping

runs on Switch A and Switch B, Host A and Host C are receiver hosts (namely, multicast

group members).

Router A Switch A

Switch B

Eth1/1/10 Eth1/1/1

Eth1/1/2

Eth1/1/10

Eth1/1/1

Receiver

Host A

Host B

Host C

Host D

Source

Multicast packets

Router port

Member port

Figure 1-2 IGMP Snooping related ports

Ports involved in IGMP Snooping, as shown in

Figure 1-2, are described as follows:

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z Router port: A router port is a port on the Layer-3 multicast device or the IGMP

querier side of the Ethernet switch. In the figure, Ethernet 1/1/10 of Switch A and

Ethernet 1/0 of Switch B are router ports. A switch registers all its local router ports

(including dynamic and static router ports) in its router port list.

z Member port: Also known as a listener port, a member port is a port on the

multicast group member side of the Ethernet switch. In the figure, Ethernet 1/1/1

and Ethernet 1/1/2 of Switch A and Ethernet 1/1/1 of Switch B are member ports.

The switch records all member ports (including dynamic and static member ports)

on the local device in the IGMP Snooping forwarding table.

 Note:

z Whenever mentioned in this document, a router port is a port on a switch that leads

the switch to a Layer 3 multicast device, rather than a port on a router.

z An IGMP-snooping-enabled switch deems all its ports on which IGMP general

queries with the source address other than 0.0.0.0 or PIM hello messages are

received to be dynamic router ports. For details about PIM hello messages, see PIM

Configuration of the IP Multicast Volume.

II. Port aging timers in IGMP Snooping and related messages and actions

Table 1-1 Port aging timers in IGMP Snooping and related messages and actions

Timer Description

Message before

expiry

Action after

expiry

Dynamic

router port

aging timer

For each dynamic router

port, the switch sets a

timer initialized to the

dynamic router port aging

time

IGMP general

query of which the

source address is

not 0.0.0.0 or PIM

hello

The switch

removes this

port from its

router port list

Dynamic

member port

aging timer

When a port dynamically

joins a multicast group, the

switch sets a timer for the

port, which is initialized to

the dynamic member port

aging time.

IGMP report

The switch

removes this

port from the

IGMP Snooping

forwarding

table.

 Note:

The port aging mechanism of IGMP Snooping works only on dynamic ports; a static

port will never age out.

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1.1.3 Work Mechanism of IGMP Snooping

Caution:

Only dynamic ports can be automatically added or deleted by the system. Static ports

can be added or deleted only through the corresponding configurations.

A switch running IGMP Snooping performs different actions when it receives different

IGMP messages, as follows:

I. When receiving a general query

The IGMP querier periodically sends IGMP general queries to all hosts and routers on

the local subnet (224.0.0.1) to find out whether active multicast group members exist

on the subnet.

Upon receiving an IGMP general query, the switch forwards it through all ports in the

VLAN except the receiving port, and performs the following to the port on which it

received the query message:

z If the port is a dynamic router port existing in the router port list, the switch resets

the aging timer for this dynamic router port.

z If the port is not a dynamic router port existing in its router port list, the switch adds

it into the router port list and sets an aging timer for this dynamic router port.

II. When receiving a membership report

A host sends an IGMP report to the IGMP querier in the following circumstances:

z Upon receiving an IGMP query, a multicast group member host responds with an

IGMP report.

z When intended to join a multicast group, a host sends an IGMP report to the IGMP

querier to announce that it is interested in the multicast information addressed to

that group.

Upon receiving an IGMP report, the switch forwards it through all the router ports in the

VLAN, resolves the address of the multicast group the host is interested in, and

performs the following to the receiving port:

z If no forwarding table entry exists for the reported group, the switch creates an

entry, adds the port as a dynamic member port into the outgoing port list, and

starts a member port aging timer for that port.

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z If a forwarding table entry exists for the reported group, but the port is not included

in the outgoing port list for that group in the forwarding entry, the switch adds the

port as a dynamic member port into the outgoing port list, and starts an aging timer

for that port.

z If a forwarding table entry exists for the reported group and the port is included in

the outgoing port list, which means that this port is already a dynamic member port

for that group, the switch resets the aging timer for that port.

 Note:

A switch will not forward an IGMP report through a non-router port.

III. When receiving a leave message

When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave

message, so the switch cannot know immediately that the host has left the multicast

group. However, as the host stops sending IGMP reports as soon as it leaves a

multicast group, the switch deletes the forwarding entry for the dynamic member port

corresponding to the host from the forwarding table when its aging timer expires.

When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP

leave message to the multicast router.

When the switch receives an IGMP leave message on a dynamic member port, the

switch first checks whether a forwarding table entry for the group address in the leave

message exists, and, if one exists, whether the outgoing port list contains that port.

z If the forwarding table entry does not exist or if the outgoing port list does not

contain the port, the switch discards the IGMP leave message instead of

forwarding it to any port.

z If the forwarding table entry exists and the outgoing port list contains the port, the

switch forwards the leave message to all router ports in the VLAN. Because the

switch does not know whether any other hosts attached to the port are still

listening to that group address, the switch does not immediately remove the port

from the outgoing port list of the forwarding table entry for that group; instead, it

resets the aging timer for the port.

Upon receiving the IGMP leave message from a host, the IGMP querier resolves the

multicast group address in the message and sends an IGMP group-specific query to

that multicast group through the port that received the leave message. Upon receiving

the IGMP group-specific query, the switch (non-IGMP querier) forwards it through all its

router ports in the VLAN and all member ports for that multicast group, and performs

the following to the port on which it received the IGMP leave message:

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z If any IGMP report in response to the group-specific query is received on the port

(suppose it is a dynamic member port) before its aging timer expires, this means

that some host attached to the port is receiving or expecting to receive multicast

data for that multicast group. The switch resets the aging timer of the port.

z If no IGMP report in response to the group-specific query is received on the port

before its aging timer expires, this means that no hosts attached to the port are still

listening to that group address: the switch removes the port from the outgoing port

list of the forwarding table entry for that multicast group when the aging timer

expires.

1.1.4 Processing of Multicast Protocol Messages

With Layer 3 multicast routing enabled, an IGMP Snooping–capable S9500 series

Ethernet switch processes multicast protocol messages differently under different

conditions, specifically as follows:

1) If only IGMP is enabled, or both IGMP and PIM are enabled on the switch, the

switch handles multicast protocol messages in the normal way.

2) In only PIM is enabled on the switch:

z The switch broadcasts IGMP messages as unknown messages in the VLAN.

z Upon receiving a PIM hello message, the switch will maintain the corresponding

router port.

3) When IGMP is disabled on the switch:

z If PIM is disabled, the switch deletes all its dynamic member ports and dynamic

router ports.

z If PIM is enabled, the switch deletes only its dynamic member ports without

deleting its dynamic router ports.

4) When PIM is disabled on the switch:

z If IGMP is disabled, the switch deletes only its dynamic router ports without

deleting its dynamic member ports.

z If IGMP is enabled, the switch maintains all its dynamic member ports and

dynamic router ports.

 Note:

On a switch with Layer-3 multicast routing enabled, use the display igmp group

port-info command to view Layer-2 port information. For details about this command,

refer to IGMP Commands in the IP Multicast Volume.

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1.1.5 Protocols and Standards

IGMP Snooping is documented in RFC 4541: Considerations for Internet Group

Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping

Switches.

1.2 IGMP Snooping Configuration Task List

Complete these tasks to configure IGMP Snooping:

Task Remarks

Enabling IGMP Snooping Required

Configuring the Version of IGMP Snooping Optional

Configuring Basic

Functions of IGMP

Snooping

Configuring the Function of Dropping

Unknown Multicast Data

Optional

Configuring Static Ports Optional

Configuring Simulated Joining Optional

Configuring Fast Leave Processing Optional

Configuring IGMP

Snooping Port

Functions

Configuring Aging Timers for Dynamic

Ports

Optional

Enabling IGMP Snooping Querier Optional

Configuring IGMP Queries and

Responses

Optional

Configuring Source IP Address of IGMP

Queries

Optional

Configuring

IGMP-Related

Functions

IGMP Snooping Configuration Optional

Configuring a Multicast Group Filter Optional

Configuring Maximum Multicast Groups

that Can Be Joined on a Port

Optional

Configuring a Multicast

Group Policy

Configuring Multicast Group Replacement Optional

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 Note:

z Configurations made in IGMP Snooping view are effective for all VLANs, while

configurations made in VLAN view are effective only for ports belonging to the

current VLAN. For a given VLAN, a configuration made in IGMP Snooping view is

effective only if the same configuration is not made in VLAN view.

z Configurations made in IGMP Snooping view are effective for all ports;

configurations made in interface view are effective only for the current interface;

configurations made in manual port group view are effective only for all the ports in

the current port group; configurations made in aggregation port group view are

effective only for the master port of the group. For a given port, a configuration made

in IGMP Snooping view is effective only if the same configuration is not made in

interface view or port group view.

1.3 Configuring Basic Functions of IGMP Snooping

1.3.1 Configuration Prerequisites

Before configuring the basic functions of IGMP Snooping, complete the following task:

z Configure the corresponding VLANs

Before configuring the basic functions of IGMP Snooping, consider the following points:

z Version of IGMP Snooping

z Whether to enable the function of dropping unknown multicast data.

1.3.2 Enabling IGMP Snooping

Follow these steps to enable IGMP Snooping:

To do... Use the command... Remarks

Enter system view

system-view

—

Enable IGMP Snooping

globally and enter IGMP

Snooping view

igmp-snooping

Required

Disabled by default

Return to system view

quit

—

Enter VLAN view

vlan vlan-id

—

Enable IGMP Snooping in

the VLAN

igmp-snooping enable

Required

Disabled by default

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 Note:

z IGMP Snooping must be enabled globally before it can be enabled in a VLAN.

z When you enable IGMP Snooping in a specified VLAN, this function takes effect for

Ethernet ports in this VLAN only.

z After enabling IGMP Snooping in a VLAN, you cannot enable IGMP and/or PIM on

the corresponding VLAN interface, and vice versa.

1.3.3 Configuring the Version of IGMP Snooping

By configuring the IGMP Snooping version, you actually configure the version of IGMP

messages that IGMP Snooping can process.

z IGMP Snooping version 2 can process IGMPv1 and IGMPv2 messages, but not

IGMPv3 messages, which will be flooded in the VLAN.

z IGMP Snooping version 3 can process IGMPv1, IGMPv2 and IGMPv3 messages.

Follow these steps to configure the version of IGMP Snooping:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter VLAN view

vlan vlan-id

—

Configure the version of

IGMP Snooping

igmp-snooping version

version-number

Optional

Version 2 by default

Caution:

If you switch IGMP Snooping from version 3 to version 2, the system will clear all IGMP

Snooping forwarding entries from dynamic joins, and will:

z Keep forwarding entries for version 3 static (*, G) joins;

z Clear forwarding entries for version 3 static (S, G) joins, which will be restored when

IGMP Snooping is switched back to version 3.

For details about static joining, refer to

Configuring Static Ports.

1.3.4 Configuring the Function of Dropping Unknown Multicast Data

Unknown multicast data refers to multicast data whose forwarding entries do not exist

in the IGMP Snooping forwarding table:

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z With the function of dropping unknown multicast data enabled, the switch drops all

the unknown multicast data received.

z With the function of dropping unknown multicast data disabled, the switch floods

unknown multicast data in the native VLAN.

Follow these steps to configure the function of dropping unknown multicast data:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter IGMP Snooping view

igmp-snooping

—

Enable the function of dropping

unknown multicast data

drop-unknown

Required

Disabled by default

 Note:

An S9500 series routing switch still forward unknown multicast data to other router

ports in the VLAN even if enabled to drop unknown multicast data.

1.4 Configuring IGMP Snooping Port Functions

1.4.1 Configuration Prerequisites

Before configuring IGMP Snooping port functions, complete the following tasks:

z Enable IGMP Snooping in the VLAN or enable IGMP on the VLAN interface

z Configure the corresponding port groups.

Before configuring IGMP Snooping port functions, consider the following points:

z Multicast group and multicast source addresses

z Whether to configure simulated joining

z Whether to enable fast leave processing

z Dynamic router port aging time

z Dynamic member port aging time

1.4.2 Configuring Static Ports

If all the hosts attached to a port are interested in the multicast data addressed to a

particular multicast group or the multicast data that a particular multicast source sends

to a particular group, you can configure static (*, G) or (S, G) joining on that port,

namely configure the port as a group-specific or source-and-group-specific static

member port.

You can configure a port of a switch to be a static router port, through which the switch

can forward all the multicast traffic it received.

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Follow these steps to configure static ports:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter Ethernet

interface view

interface interface-type

interface-number

Enter the

corresponding

view

Enter interface

group view

port-group { manual

port-group-name |

aggregation agg-id }

Required

Use either

command

Configure the port(s) as static

member port(s)

igmp-snooping

static-group group-address

[ source-ip

source_address ] vlan

vlan-id

Required

A port is not a

static member

port by default

Configure the port(s) as static

router port(s)

igmp-snooping

static-router-port vlan

vlan-id

Required

A port is not a

static router

port by default

 Note:

z A static (S, G) joining configuration can take effect only if a valid multicast source

address is specified and IGMP Snooping version 3 is currently running on the

switch.

z A static member port does not respond to queries from the IGMP querier; when

static (*, G) or (S, G) joining is enabled or disabled on a port, the port does not send

an unsolicited IGMP report or an IGMP leave message.

z Static member ports and static router ports never age out. To remove such a port,

you need to use the corresponding undo command.

1.4.3 Configuring Simulated Joining

Generally, a host running IGMP responds to IGMP queries from the IGMP querier. If a

host fails to respond due to some reasons, the multicast router may deem that no

member of this multicast group exists on the network segment, and therefore will

remove the corresponding forwarding path.

To avoid this situation from happening, you can enable simulated joining on a port of

the switch, namely configure the port as a simulated member host for a multicast group.

When an IGMP query is received, the simulated host gives a response. Thus, the

switch can continue receiving multicast data.

A simulated host acts like a real host, as follows:

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z When a port is configured as a simulated member host, the switch sends an

unsolicited IGMP report through that port.

z After a port is configured as a simulated member host, the switch responds to

IGMP general queries by sending IGMP reports through that port.

z When the simulated joining function is disabled on a port, the switch sends an

IGMP leave message through that port.

Follow these steps to configure simulated joining:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter Ethernet

interface view

interface interface-type

interface-number

Enter the

correspon

ding view

Enter interface

group view

port-group { manual

port-group-name |

aggregation agg-id }

Use either command

Configure simulated (*, G)

or (S, G) joining

igmp-snooping host-join

group-address [ source-ip

source-address ] vlan

vlan-id

Required

Disabled by default

 Note:

z Each simulated host is equivalent to an independent host. For example, when

receiving an IGMP query, the simulated host corresponding to each configuration

responds respectively.

z Unlike a static member port, a port configured as a simulated member host will age

out like a dynamic member port.

1.4.4 Configuring Fast Leave Processing

The fast leave processing feature allows the switch to process IGMP leave messages

in a fast way. With the fast leave processing feature enabled, when receiving an IGMP

leave message on a port, the switch immediately removes that port from the outgoing

port list of the forwarding table entry for the indicated group. Then, when receiving

IGMP group-specific queries for that multicast group, the switch will not forward them to

that port.

In VLANs where only one host is attached to each port, fast leave processing helps

improve bandwidth and resource usage.

I. Configuring fast leave processing globally

Follow these steps to configure fast leave processing globally:

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To do... Use the command... Remarks

Enter system view

system-view

—

Enter IGMP Snooping

view

igmp-snooping

—

Enable fast leave

processing

fast-leave [ vlan vlan-list ]

Required

Disabled by default

II. Configuring fast leave processing on a port or a group of ports

Follow these steps to configure fast leave processing on a port or a group of ports:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter

Ethernet

interface view

interface interface-type

interface-number

Enter the

correspon

ding view

Enter

interface

group view

port-group { manual

port-group-name |

aggregation agg-id }

Use either

command

Enable fast leave

processing

igmp-snooping fast-leave

[ vlan vlan-list ]

Required

Disabled by default

Caution:

z If fast leave processing is enabled on a port to which more than one host is attached,

when one host leaves a multicast group, the other hosts attached to the port and

interested in the same multicast group will fail to receive multicast data for that

group.

z Fast leave processing is effective on a port only when IGMPv2 or IGMPv3 runs on

all the hosts of a multicast group attached to this port. If IGMPv1 runs on a host, fast

leave processing does not take effect even if it is configured.

1.4.5 Configuring Aging Timers for Dynamic Ports

If the switch receives no IGMP general queries or PIM hello messages on a dynamic

router port, the switch removes the port from the router port list when the aging timer of

the port expires.

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If the switch receives no IGMP reports for a multicast group on a dynamic member port,

the switch removes the port from the outgoing port list of the forwarding table entry for

that multicast group when the aging timer of the port for that group expires.

If multicast group memberships change frequently, you can set a relatively small value

for the dynamic member port aging timer, and vice versa.

I. Configuring aging timers for dynamic ports globally

Follow these steps to configure aging timers for dynamic ports globally:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter IGMP Snooping

view

igmp-snooping

—

Configure dynamic router

port aging time

router-aging-time

interval

Optional

105 seconds by default

Configure dynamic

member port aging time

host-aging-time interval

Optional

260 seconds by default

II. Configuring aging timers for dynamic ports in a VLAN

Follow these steps to configure aging timers for dynamic ports in a VLAN:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter VLAN view

vlan vlan-id

—

Configure dynamic router

port aging time

igmp-snooping

router-aging-time

interval

Optional

105 seconds by default

Configure dynamic

member port aging time

igmp-snooping

host-aging-time interval

Optional

260 seconds by default

1.5 Configuring IGMP-Related Functions

1.5.1 Configuration Prerequisites

Before configuring IGMP-related functions, complete the following task:

z Enable IGMP Snooping in the VLAN

Before configuring IGMP-related functions, consider the following points:

z IGMP general query interval

z IGMP last-member query interval

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z Maximum response time to IGMP general queries

z Source address of IGMP general queries

z Source address of IGMP group-specific queries

z Whether to enable IGMP report suppression

1.5.2 Enabling IGMP Snooping Querier

In an IP multicast network running IGMP, a Layer 3 multicast device acts as the IGMP

querier, which periodically sends IGMP queries so that all Layer 3 multicast devices can

create and maintain multicast forwarding entries at the network layer, thus to forward

multicast traffic correctly at the network layer.

In a network that does not comprise Layer 3 multicast devices, however, it is a problem

to implement an IGMP querier, because Layer 2 devices do not support IGMP. To solve

this problem, you can enable the IGMP Snooping querier function on a Layer 2 device

so that it can work as an IGMP Snooping querier to create and maintain multicast

forwarding entries at the data link layer.

Follow these steps to enable IGMP Snooping querier:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter VLAN view

vlan vlan-id

—

Enable IGMP Snooping

querier

igmp-snooping querier

Required

Disabled by default

Caution:

z An IGMP Snooping querier does not take part in IGMP querier elections.

z It is meaningless to configure an IGMP Snooping querier in a multicast network

running IGMP. It may affect IGMP querier elections because it sends IGMP general

queries with a low source IP address.

z When a device is configured as the IGMP Snooping querier of multiple attached

subnets, excessive query tasks will affect device performance. In this case, you can

configure properly longer query intervals than usual.

1.5.3 Configuring IGMP Queries and Responses

You can tune the IGMP general query interval based on actual condition of the network.

Upon receiving an IGMP query (general query or group-specific query), a host starts a

timer for each multicast group it has joined. This timer is initialized to a random value in

Operation Manual – IGMP Snooping

H3C S9500 Series Routing Switches Chapter 1 IGMP Snooping Configuration

1-16

the range of 0 to the maximum response time (the host obtains the value of the

maximum response time from the Max Response Time field in the IGMP query it

received). When the timer value comes down to 0, the host sends an IGMP report to the

corresponding multicast group.

An appropriate setting of the maximum response time for IGMP queries allows hosts to

respond to queries quickly and avoids bursts of IGMP traffic on the network caused by

reports simultaneously sent by a large number of hosts when corresponding timers

expires simultaneously.

z For IGMP general queries, you can configure the maximum response time to fill

their Max Response time field.

z For IGMP group-specific queries, you can configure the IGMP last-member query

interval to fill their Max Response time field. Namely, for IGMP group-specific

queries, the maximum response time equals to the IGMP last-member query

interval.

I. Configuring IGMP queries and responses globally

Follow these steps to configure IGMP queries and responses globally:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter IGMP Snooping

view

igmp-snooping

—

Configure the maximum

response time to IGMP

general queries

max-response-time

interval

Optional

10 seconds by default

Configure the IGMP

last-member query

interval

last-member-query-inter

val interval

Optional

1 second by default

II. Configuring IGMP queries and responses in a VLAN

Follow these steps to configure IGMP queries and responses in a VLAN:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter VLAN view

vlan vlan-id

—

Configure IGMP general

query interval

igmp-snooping

query-interval interval

Optional

60 second by default

Configure the maximum

response time to IGMP

general queries

igmp-snooping

max-response-time

interval

Optional

10 seconds by default

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H3C S9500 Series Routing Switches Chapter 1 IGMP Snooping Configuration

1-17

To do... Use the command... Remarks

Configure the IGMP

last-member query

interval

igmp-snooping

last-member-query-inter

val interval

Optional

1 second by default

Caution:

Make sure that the IGMP general query interval is larger than the maximum response

time for IGMP general queries. Otherwise, multicast group members may be deleted by

mistake.

1.5.4 Configuring Source IP Address of IGMP Queries

Upon receiving an IGMP query whose source IP address is 0.0.0.0 on a port, the switch

will not set that port as a dynamic router port. This may prevent multicast forwarding

entries from being correctly created at the data link layer and cause multicast traffic

forwarding failure in the end. When a Layer-2 device acts as an IGMP-Snooping querier,

to avoid the aforesaid problem, you are commended configure a non-all-zero IP

address as the source IP address of IGMP queries.

Follow these steps to configure source IP address of IGMP queries:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter VLAN view

vlan vlan-id

—

Configure the source

address of IGMP general

queries

igmp-snooping general-query

source-ip { current-interface |

ip-address }

Optional

0.0.0.0 by default

Configure the source IP

address of IGMP

group-specific queries

igmp-snooping special-query

source-ip { current-interface |

ip-address }

Optional

0.0.0.0 by default

Caution:

The source address of IGMP query messages may affect IGMP querier election within

the segment.

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H3C S9500 Series Routing Switches Chapter 1 IGMP Snooping Configuration

1-18

1.5.5 Configuring IGMP Report Suppression

When a Layer 2 device receives an IGMP report from a multicast group member, the

device forwards the message to the Layer 3 device directly connected with it. Thus,

when multiple members of a multicast group are attached to the Layer 2 device, the

Layer 3 device directly connected with it will receive duplicate IGMP reports from these

members.

With the IGMP report suppression function enabled, within each query cycle, the Layer

2 device forwards only the first IGMP report per multicast group to the Layer 3 device

and will not forward the subsequent IGMP reports from the same multicast group to the

Layer 3 device. This helps reduce the number of packets being transmitted over the

network.

Follow these steps to configure IGMP report suppression:

To do... Use the command... Remarks

Enter system view

system-view

—

Enter IGMP Snooping

view

igmp-snooping

—

Enable IGMP report

suppression

report-aggregation

Optional

Enabled by default

1.6 Configuring a Multicast Group Policy

1.6.1 Configuration Prerequisites

Before configuring a multicast group filtering policy, complete the following tasks:

z Enable IGMP Snooping in the VLAN or enable IGMP on the desired VLAN

interface

z Configure the corresponding port group

Before configuring a multicast group filtering policy, consider the following points:

z ACL rule for multicast group filtering

z The maximum number of multicast groups that can be joined on a port

z Whether to configure multicast group replacement

1.6.2 Configuring a Multicast Group Filter

On an IGMP Snooping–enabled switch, the configuration of a multicast group allows

the service provider to define limits of multicast programs available to different users.

In an actual application, when a user requests a multicast program, the user’s host

initiates an IGMP report. Upon receiving this report message, the switch checks the

report against the ACL rule configured on the receiving port. If the receiving port can

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H3C S9500 Series Operating instructions

Brand: H3C

Model: S9500 Series

Category: Network switches

Type: Operating instructions

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H3C S9500 Series Operating instructions

H3C S9500 Series Operating instructions

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