Configuring IGMP Snooping

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Prerequisites for Configuring IGMP Snooping

Prerequisites for IGMP Snooping

Observe these guidelines when configuring the IGMP snooping querier:

  • Configure the VLAN in global configuration mode.

  • Configure an IP address on the VLAN interface. When enabled, the IGMP snooping querier uses the IP address as the query source address.

  • If there is no IP address configured on the VLAN interface, the IGMP snooping querier tries to use the configured global IP address for the IGMP querier. If there is no global IP address specified, the IGMP querier tries to use the VLAN device virtual interface (SVI) IP address (if one exists). If there is no SVI IP address, the device uses the first available IP address configured on the device. The first IP address available appears in the output of the show ip interface privileged EXEC command. The IGMP snooping querier does not generate an IGMP general query if it cannot find an available IP address on the device.

  • The IGMP snooping querier supports IGMP Versions 1 and 2.

  • When administratively enabled, the IGMP snooping querier moves to the nonquerier state if it detects the presence of a multicast router in the network.

  • When it is administratively enabled, the IGMP snooping querier moves to the operationally disabled state if IGMP snooping is disabled in the VLAN.

  • Layer 3 multicast is not supported.

  • MAC based snooping is supported in hardware.

Restrictions for Configuring IGMP Snooping

Restrictions for IGMP Snooping

The following are the restrictions for IGMP snooping:

  • The switch supports homogeneous stacking and mixed stacking. Mixed stacking is supported only with the Catalyst 2960-S switches. A homogenous stack can have up to eight stack members, while a mixed stack can have up to four stack members. All switches in a switch stack must be running the LAN Base image.

  • IGMPv3 join and leave messages are not supported on devices running IGMP filtering or Multicast VLAN registration (MVR).

  • IGMP report suppression is supported only when the multicast query has IGMPv1 and IGMPv2 reports. This feature is not supported when the query includes IGMPv3 reports.

  • The IGMP configurable leave time is only supported on hosts running IGMP Version 2. IGMP version 2 is the default version for the device.

    The actual leave latency in the network is usually the configured leave time. However, the leave time might vary around the configured time, depending on real-time CPU load conditions, network delays and the amount of traffic sent through the interface.

  • The IGMP throttling action restriction can be applied only to Layer 2 ports. You can use ip igmp max-groups action replace interface configuration command on a logical EtherChannel interface but cannot use it on ports that belong to an EtherChannel port group.

    When the maximum group limitation is set to the default (no maximum), entering the ip igmp max-groups action {deny | replace} command has no effect.

    If you configure the throttling action and set the maximum group limitation after an interface has added multicast entries to the forwarding table, the forwarding-table entries are either aged out or removed, depending on the throttling action.

Information About IGMP Snooping

IGMP Snooping

Layer 2 devices can use IGMP snooping to constrain the flooding of multicast traffic by dynamically configuring Layer 2 interfaces so that multicast traffic is forwarded to only those interfaces associated with IP multicast devices. As the name implies, IGMP snooping requires the LAN device to snoop on the IGMP transmissions between the host and the router and to keep track of multicast groups and member ports. When the device receives an IGMP report from a host for a particular multicast group, the device adds the host port number to the forwarding table entry; when it receives an IGMP Leave Group message from a host, it removes the host port from the table entry. It also periodically deletes entries if it does not receive IGMP membership reports from the multicast clients.


Note

For more information on IP multicast and IGMP, see RFC 1112 and RFC 2236.

The multicast router sends out periodic general queries to all VLANs. All hosts interested in this multicast traffic send join requests and are added to the forwarding table entry. The device creates one entry per VLAN in the IGMP snooping IP multicast forwarding table for each group from which it receives an IGMP join request.

The device supports IP multicast group-based bridging, instead of MAC-addressed based groups. With multicast MAC address-based groups, if an IP address being configured translates (aliases) to a previously configured MAC address or to any reserved multicast MAC addresses (in the range 224.0.0.xxx), the command fails. Because the device uses IP multicast groups, there are no address aliasing issues.

The IP multicast groups learned through IGMP snooping are dynamic. However, you can statically configure multicast groups by using the ip igmp snooping vlan vlan-id static ip_address interface interface-id global configuration command. If you specify group membership for a multicast group address statically, your setting supersedes any automatic manipulation by IGMP snooping. Multicast group membership lists can consist of both user-defined and IGMP snooping-learned settings.

You can configure an IGMP snooping querier to support IGMP snooping in subnets without multicast interfaces because the multicast traffic does not need to be routed.

If a port spanning-tree, a port group, or a VLAN ID change occurs, the IGMP snooping-learned multicast groups from this port on the VLAN are deleted.

These sections describe IGMP snooping characteristics:

IGMP Versions

The device supports IGMP version 1, IGMP version 2, and IGMP version 3. These versions are interoperable on the device. For example, if IGMP snooping is enabled and the querier's version is IGMPv2, and the device receives an IGMPv3 report from a host, then the device can forward the IGMPv3 report to the multicast router.

An IGMPv3 device can receive messages from and forward messages to a device running the Source Specific Multicast (SSM) feature.

Joining a Multicast Group

Figure 1. Initial IGMP Join Message.

When a host connected to the device wants to join an IP multicast group and it is an IGMP version 2 client, it sends an unsolicited IGMP join message, specifying the IP multicast group to join. Alternatively, when the device receives a general query from the router, it forwards the query to all ports in the VLAN. IGMP version 1 or version 2 hosts wanting to join the multicast group respond by sending a join message to the device. The device CPU creates a multicast forwarding-table entry for the group if it is not already present. The CPU also adds the interface where the join message was received to the forwarding-table entry. The host associated with that interface receives multicast traffic for that multicast group.

Router A sends a general query to the device, which forwards the query to ports 2 through 5, all of which are members of the same VLAN. Host 1 wants to join multicast group 224.1.2.3 and multicasts an IGMP membership report (IGMP join message) to the group. The device CPU uses the information in the IGMP report to set up a forwarding-table entry that includes the port numbers connected to Host 1 and to the router.

Table 1. IGMP Snooping Forwarding Table

Destination Address

Type of Packet

Ports

224.1.2.3

IGMP

1, 2

The device hardware can distinguish IGMP information packets from other packets for the multicast group. The information in the table tells the switching engine to send frames addressed to the 224.1.2.3 multicast IP address that are not IGMP packets to the router and to the host that has joined the group.

Figure 2. Second Host Joining a Multicast Group. If another host (for example, Host 4) sends an unsolicited IGMP join message for the same group, the CPU receives that message and adds the port number of Host 4 to the forwarding table. Because the forwarding table directs IGMP messages only to the CPU, the message is not flooded to other ports on the device. Any known multicast traffic is forwarded to the group and not to the CPU.
Table 2. Updated IGMP Snooping Forwarding Table

Destination Address

Type of Packet

Ports

224.1.2.3

IGMP

1, 2, 5

Leaving a Multicast Group

The router sends periodic multicast general queries, and the device forwards these queries through all ports in the VLAN. Interested hosts respond to the queries. If at least one host in the VLAN wants to receive multicast traffic, the router continues forwarding the multicast traffic to the VLAN. The device forwards multicast group traffic only to those hosts listed in the forwarding table for that IP multicast group maintained by IGMP snooping.

When hosts want to leave a multicast group, they can silently leave, or they can send a leave message. When the device receives a leave message from a host, it sends a group-specific query to learn if any other devices connected to that interface are interested in traffic for the specific multicast group. The device then updates the forwarding table for that MAC group so that only those hosts interested in receiving multicast traffic for the group are listed in the forwarding table. If the router receives no reports from a VLAN, it removes the group for the VLAN from its IGMP cache.

Immediate Leave

The device uses IGMP snooping Immediate Leave to remove from the forwarding table an interface that sends a leave message without the device sending group-specific queries to the interface. The VLAN interface is pruned from the multicast tree for the multicast group specified in the original leave message. Immediate Leave ensures optimal bandwidth management for all hosts on a switched network, even when multiple multicast groups are simultaneously in use.

Immediate Leave is only supported on IGMP version 2 hosts. IGMP version 2 is the default version for the device.


Note

You should use the Immediate Leave feature only on VLANs where a single host is connected to each port. If Immediate Leave is enabled on VLANs where more than one host is connected to a port, some hosts may be dropped inadvertently.

IGMP Configurable-Leave Timer

You can configure the time that the device waits after sending a group-specific query to determine if hosts are still interested in a specific multicast group. The IGMP leave response time can be configured from 100 to 32767 milliseconds.

IGMP Report Suppression


Note

IGMP report suppression is supported only when the multicast query has IGMPv1 and IGMPv2 reports. This feature is not supported when the query includes IGMPv3 reports.

The device uses IGMP report suppression to forward only one IGMP report per multicast router query to multicast devices. When IGMP report suppression is enabled (the default), the device sends the first IGMP report from all hosts for a group to all the multicast routers. The device does not send the remaining IGMP reports for the group to the multicast routers. This feature prevents duplicate reports from being sent to the multicast devices.

If the multicast router query includes requests only for IGMPv1 and IGMPv2 reports, the device forwards only the first IGMPv1 or IGMPv2 report from all hosts for a group to all the multicast routers.

If the multicast router query also includes requests for IGMPv3 reports, the device forwards all IGMPv1, IGMPv2, and IGMPv3 reports for a group to the multicast devices.

If you disable IGMP report suppression, all IGMP reports are forwarded to the multicast routers.

Default IGMP Snooping Configuration

This table displays the default IGMP snooping configuration for the device.

Table 3. Default IGMP Snooping Configuration

Feature

Default Setting

IGMP snooping

Enabled globally and per VLAN

Multicast routers

None configured

IGMP snooping Immediate Leave

Disabled

Static groups

None configured

TCN1 flood query count

2

TCN query solicitation

Disabled

IGMP snooping querier

Disabled

IGMP report suppression

Enabled

1 (1) TCN = Topology Change Notification

IGMP Filtering and Throttling

In some environments, for example, metropolitan or multiple-dwelling unit (MDU) installations, you might want to control the set of multicast groups to which a user on a device port can belong. You can control the distribution of multicast services, such as IP/TV, based on some type of subscription or service plan. You might also want to limit the number of multicast groups to which a user on a device port can belong.

With the IGMP filtering feature, you can filter multicast joins on a per-port basis by configuring IP multicast profiles and associating them with individual device ports. An IGMP profile can contain one or more multicast groups and specifies whether access to the group is permitted or denied. If an IGMP profile denying access to a multicast group is applied to a device port, the IGMP join report requesting the stream of IP multicast traffic is dropped, and the port is not allowed to receive IP multicast traffic from that group. If the filtering action permits access to the multicast group, the IGMP report from the port is forwarded for normal processing. You can also set the maximum number of IGMP groups that a Layer 2 interface can join.

IGMP filtering controls only group-specific query and membership reports, including join and leave reports. It does not control general IGMP queries. IGMP filtering has no relationship with the function that directs the forwarding of IP multicast traffic.

IGMP filtering applies only to the dynamic learning of IP multicast group addresses, not static configuration.

With the IGMP throttling feature, you can set the maximum number of IGMP groups that a Layer 2 interface can join. If the maximum number of IGMP groups is set, the IGMP snooping forwarding table contains the maximum number of entries, and the interface receives an IGMP join report, you can configure an interface to drop the IGMP report or to replace the randomly selected multicast entry with the received IGMP report.


Note

IGMPv3 join and leave messages are not supported on devices running IGMP filtering.

Default IGMP Filtering and Throttling Configuration

This table displays the default IGMP filtering and throttling configuration for the device.

Table 4. Default IGMP Filtering Configuration

Feature

Default Setting

IGMP filters

None applied.

IGMP maximum number of IGMP groups

No maximum set.

Note

 

When the maximum number of groups is in the forwarding table, the default IGMP throttling action is to deny the IGMP report.

IGMP profiles

None defined.

IGMP profile action

Deny the range addresses.

How to Configure IGMP Snooping

Enabling or Disabling IGMP Snooping on a Device

When IGMP snooping is globally enabled or disabled, it is also enabled or disabled in all existing VLAN interfaces. IGMP snooping is enabled on all VLANs by default, but can be enabled and disabled on a per-VLAN basis.

Global IGMP snooping overrides the VLAN IGMP snooping. If global snooping is disabled, you cannot enable VLAN snooping. If global snooping is enabled, you can enable or disable VLAN snooping.

Follow these steps to globally enable IGMP snooping on the device:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping
  4. end
  5. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping

Example:


Device(config)# ip igmp snooping

Globally enables IGMP snooping in all existing VLAN interfaces.

Note

 

To globally disable IGMP snooping on all VLAN interfaces, use the no ip igmp snooping global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Enabling or Disabling IGMP Snooping on a VLAN Interface

Follow these steps to enable IGMP snooping on a VLAN interface:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping vlan vlan-id
  4. end
  5. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping vlan vlan-id

Example:


Device(config)# ip igmp snooping vlan 7

Enables IGMP snooping on the VLAN interface. The VLAN ID range is 1 to 1001 and 1006 to 4094.

IGMP snooping must be globally enabled before you can enable VLAN snooping.

Note

 

To disable IGMP snooping on a VLAN interface, use the no ip igmp snooping vlan vlan-id global configuration command for the specified VLAN number.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Setting the Snooping Method

Multicast-capable router ports are added to the forwarding table for every Layer 2 multicast entry. The switch learns of the ports through one of these methods:

  • Snooping on IGMP queries, Protocol-Independent Multicast (PIM) packets, and Distance Vector Multicast Routing Protocol (DVMRP) packets.

  • Listening to Cisco Group Management Protocol (CGMP) packets from other routers.

  • Statically connecting to a multicast router port using the ip igmp snooping mrouter global configuration command.


Note

Static connection using the ip igmp snooping mrouter command is supported only for known multicast groups.

You can configure the switch either to snoop on IGMP queries and PIM/DVMRP packets or to listen to CGMP self-join or proxy-join packets. By default, the switch snoops on PIM/DVMRP packets on all VLANs. To learn of multicast router ports through only CGMP packets, use the ip igmp snooping vlan vlan-id mrouter learn cgmp global configuration command. When this command is entered, the router listens to only CGMP self-join and CGMP proxy-join packets and to no other CGMP packets. To learn of multicast router ports through only PIM-DVMRP packets, use the ip igmp snooping vlan vlan-id mrouter learn pim-dvmrp global configuration command.

If you want to use CGMP as the learning method and no multicast routers in the VLAN are CGMP proxy-enabled, you must enter the ip cgmp router-only command to dynamically access the router.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping vlan vlan-id mrouter learn {cgmp | pim-dvmrp }
  4. end
  5. show ip igmp snooping
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping vlan vlan-id mrouter learn {cgmp | pim-dvmrp }

Example:

Device(config)# ip igmp snooping 
vlan 1 mrouter learn cgmp

Specifies the multicast router learning method:

  • cgmp —Listens for CGMP packets. This method is useful for reducing control traffic.

  • pim-dvmrp —Snoops on IGMP queries and PIM-DVMRP packets. This is the default.

Note

 

To return to the default learning method, use the no ip igmp snooping vlan vlan-id mrouter learn cgmp global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping

Example:


Device# show ip igmp snooping

Verifies the configuration.

Step 6

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configuring a Multicast Router Port

Perform these steps to add a multicast router port (enable a static connection to a multicast router) on the device.


Note

Static connections to multicast routers are supported only on device ports.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping vlan vlan-id mrouter interface interface-id
  4. end
  5. show ip igmp snooping mrouter [vlan vlan-id]
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping vlan vlan-id mrouter interface interface-id

Example:


Device(config)# ip igmp snooping vlan 5 mrouter interface gigabitethernet0/1

Specifies the multicast router VLAN ID and the interface to the multicast router.

  • The VLAN ID range is 1 to 1001 and 1006 to 4094.

  • The interface can be a physical interface or a port channel. The port-channel range is 1 to 128.

Note

 

To remove a multicast router port from the VLAN, use the no ip igmp snooping vlan vlan-id mrouter interface interface-id global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping mrouter [vlan vlan-id]

Example:


Device# show ip igmp snooping mrouter vlan 5

Verifies that IGMP snooping is enabled on the VLAN interface.

Step 6

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Enabling IGMP Immediate Leave

When you enable IGMP Immediate Leave, the device immediately removes a port when it detects an IGMP Version 2 leave message on that port. You should use the Immediate-Leave feature only when there is a single receiver present on every port in the VLAN.


Note

Immediate Leave is supported only on IGMP Version 2 hosts. IGMP Version 2 is the default version for the device.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping vlan vlan-id immediate-leave
  4. end
  5. show ip igmp snooping vlan vlan-id
  6. end

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping vlan vlan-id immediate-leave

Example:


Device(config)# ip igmp snooping vlan 21 immediate-leave

Enables IGMP Immediate Leave on the VLAN interface.

Note

 

To disable IGMP Immediate Leave on a VLAN, use the no ip igmp snooping vlan vlan-id immediate-leave global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping vlan vlan-id

Example:


Device# show ip igmp snooping vlan 21

Verifies that Immediate Leave is enabled on the VLAN interface.

Step 6

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Configuring the IGMP Leave Timer

You can configure the leave time globally or on a per-VLAN basis. Follow these steps to enable the IGMP configurable-leave timer:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping last-member-query-interval time
  4. ip igmp snooping vlan vlan-id last-member-query-interval time
  5. end
  6. show ip igmp snooping
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping last-member-query-interval time

Example:


Device(config)# ip igmp snooping last-member-query-interval 1000

Configures the IGMP leave timer globally. The range is 100 to 32767 milliseconds.

The default leave time is 1000 milliseconds.

Note

 

To globally reset the IGMP leave timer to the default setting, use the no ip igmp snooping last-member-query-interval global configuration command.

Step 4

ip igmp snooping vlan vlan-id last-member-query-interval time

Example:


Device(config)# ip igmp snooping vlan 210 last-member-query-interval 1000

(Optional) Configures the IGMP leave time on the VLAN interface. The range is 100 to 32767 milliseconds.

Note

 

Configuring the leave time on a VLAN overrides the globally configured timer.

Note

 

To remove the configured IGMP leave-time setting from the specified VLAN, use the no ip igmp snooping vlan vlan-id last-member-query-interval global configuration command.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show ip igmp snooping

Example:


Device# show ip igmp snooping

(Optional) Displays the configured IGMP leave time.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configuring TCN-Related Commands

Controlling the Multicast Flooding Time After a TCN Event

You can configure the number of general queries by which multicast data traffic is flooded after a topology change notification (TCN) event. If you set the TCN flood query count to 1 the flooding stops after receiving 1 general query. If you set the count to 7, the flooding continues until 7 general queries are received. Groups are relearned based on the general queries received during the TCN event.

Some examples of TCN events are when the client location is changed and the receiver is on same port that was blocked but is now forwarding, and when a port goes down without sending a leave message.

Follow these steps to configure the TCN flood query count:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping tcn flood query count count
  4. end
  5. show ip igmp snooping
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping tcn flood query count count

Example:


Device(config)# ip igmp snooping tcn flood query count 3

Specifies the number of IGMP general queries for which the multicast traffic is flooded.

The range is 1 to 10. The default, the flooding query count is 2.

Note

 

To return to the default flooding query count, use the no ip igmp snooping tcn flood query count global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping

Example:


Device# show ip igmp snooping

Verifies the TCN settings.

Step 6

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Recovering from Flood Mode

When a topology change occurs, the spanning-tree root sends a special IGMP leave message (also known as global leave) with the group multicast address 0.0.0.0. However, you can enable the device to send the global leave message whether it is the spanning-tree root or not. When the router receives this special leave, it immediately sends general queries, which expedite the process of recovering from the flood mode during the TCN event. Leaves are always sent if the device is the spanning-tree root regardless of this configuration.

Follow these steps to enable sending of leave messages:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping tcn query solicit
  4. end
  5. show ip igmp snooping
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping tcn query solicit

Example:


Device(config)# ip igmp snooping tcn query solicit

Sends an IGMP leave message (global leave) to speed the process of recovering from the flood mode caused during a TCN event. By default, query solicitation is disabled.

Note

 

To return to the default query solicitation, use the no ip igmp snooping tcn query solicit global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping

Example:


Device# show ip igmp snooping

Verifies the TCN settings.

Step 6

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Disabling Multicast Flooding During a TCN Event

When the device receives a TCN, multicast traffic is flooded to all the ports until 2 general queries are received. If the device has many ports with attached hosts that are subscribed to different multicast groups, this flooding might exceed the capacity of the link and cause packet loss. Follow these steps to control TCN flooding:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface interface-id
  4. no ip igmp snooping tcn flood
  5. end
  6. show ip igmp snooping
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet 0/1

Specifies the interface to be configured, and enters interface configuration mode.

Step 4

no ip igmp snooping tcn flood

Example:


Device(config-if)# no ip igmp snooping tcn flood

Disables the flooding of multicast traffic during a spanning-tree TCN event.

By default, multicast flooding is enabled on an interface.

Note

 

To re-enable multicast flooding on an interface, use the ip igmp snooping tcn flood interface configuration command.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show ip igmp snooping

Example:


Device# show ip igmp snooping

Verifies the TCN settings.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configuring the IGMP Snooping Querier

Follow these steps to enable the IGMP snooping querier feature in a VLAN:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping querier
  4. ip igmp snooping querier address ip_address
  5. ip igmp snooping querier query-interval interval-count
  6. ip igmp snooping querier tcn query [count count | interval interval]
  7. ip igmp snooping querier timer expiry timeout
  8. ip igmp snooping querier version version
  9. end
  10. show ip igmp snooping vlan vlan-id
  11. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping querier

Example:


Device(config)# ip igmp snooping querier

Enables the IGMP snooping querier.

Step 4

ip igmp snooping querier address ip_address

Example:


Device(config)# ip igmp snooping querier address 172.16.24.1

(Optional) Specifies an IP address for the IGMP snooping querier. If you do not specify an IP address, the querier tries to use the global IP address configured for the IGMP querier.

Note

 

The IGMP snooping querier does not generate an IGMP general query if it cannot find an IP address on the device.

Step 5

ip igmp snooping querier query-interval interval-count

Example:


Device(config)# ip igmp snooping querier query-interval 30

(Optional) Sets the interval between IGMP queriers. The range is 1 to 18000 seconds.

Step 6

ip igmp snooping querier tcn query [count count | interval interval]

Example:


Device(config)# ip igmp snooping querier tcn query interval 20

(Optional) Sets the time between Topology Change Notification (TCN) queries. The count range is 1 to 10. The interval range is 1 to 255 seconds.

Step 7

ip igmp snooping querier timer expiry timeout

Example:


Device(config)# ip igmp snooping querier timer expiry 180

(Optional) Sets the length of time until the IGMP querier expires. The range is 60 to 300 seconds.

Step 8

ip igmp snooping querier version version

Example:


Device(config)# ip igmp snooping querier version 2

(Optional) Selects the IGMP version number that the querier feature uses. Select 1 or 2.

Step 9

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 10

show ip igmp snooping vlan vlan-id

Example:


Device# show ip igmp snooping vlan 30

(Optional) Verifies that the IGMP snooping querier is enabled on the VLAN interface. The VLAN ID range is 1 to 1001 and 1006 to 4094.

Step 11

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Disabling IGMP Report Suppression

Follow these steps to disable IGMP report suppression:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. no ip igmp snooping report-suppression
  4. end
  5. show ip igmp snooping
  6. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

no ip igmp snooping report-suppression

Example:


Device(config)# no ip igmp snooping report-suppression

Disables IGMP report suppression. When report suppression is disabled, all IGMP reports are forwarded to the multicast routers.

IGMP report suppression is enabled by default.

When IGMP report supression is enabled, the device forwards only one IGMP report per multicast router query.

Note

 

To re-enable IGMP report suppression, use the ip igmp snooping report-suppression global configuration command.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 5

show ip igmp snooping

Example:


Device# show ip igmp snooping

Verifies that IGMP report suppression is disabled.

Step 6

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configuring IGMP Profiles

Follow these steps to create an IGMP profile:

This task is optional.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp profile profile number
  4. permit | deny
  5. range ip multicast address
  6. end
  7. show ip igmp profile profile number
  8. show running-config
  9. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp profile profile number

Example:


Device(config)# ip igmp profile 3
Assigns a number to the profile you are configuring, and enters IGMP profile configuration mode. The profile number range is 1 to 4294967295. When you are in IGMP profile configuration mode, you can create the profile by using these commands:

  • deny —Specifies that matching addresses are denied; this is the default.

  • exit —Exits from igmp-profile configuration mode.

  • no —Negates a command or returns to its defaults.

  • permit —Specifies that matching addresses are permitted.

  • range —Specifies a range of IP addresses for the profile. You can enter a single IP address or a range with a start and an end address.

The default is for the device to have no IGMP profiles configured.

Note

 
To delete a profile, use the no ip igmp profile profile number global configuration command.

Step 4

permit | deny

Example:


Device(config-igmp-profile)# permit

(Optional) Sets the action to permit or deny access to the IP multicast address. If no action is configured, the default for the profile is to deny access.

Step 5

range ip multicast address

Example:


Device(config-igmp-profile)# range 229.9.9.0

Enters the IP multicast address or range of IP multicast addresses to which access is being controlled. If entering a range, enter the low IP multicast address, a space, and the high IP multicast address.

You can use the range command multiple times to enter multiple addresses or ranges of addresses.

Note

 

To delete an IP multicast address or range of IP multicast addresses, use the no range ip multicast address IGMP profile configuration command.

Step 6

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 7

show ip igmp profile profile number

Example:


Device# show ip igmp profile 3

Verifies the profile configuration.

Step 8

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 9

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Applying IGMP Profiles

To control access as defined in an IGMP profile, you have to apply the profile to the appropriate interfaces. You can apply IGMP profiles only to Layer 2 access ports; you cannot apply IGMP profiles to routed ports or SVIs. You cannot apply profiles to ports that belong to an EtherChannel port group. You can apply a profile to multiple interfaces, but each interface can have only one profile applied to it.

Follow these steps to apply an IGMP profile to a switch port:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface interface-id
  4. ip igmp filter profile number
  5. end
  6. show running-config
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet0/1

Specifies the physical interface, and enters interface configuration mode. The interface must be a Layer 2 port that does not belong to an EtherChannel port group.

Step 4

ip igmp filter profile number

Example:


Device(config-if)# ip igmp filter 321

Applies the specified IGMP profile to the interface. The range is 1 to 4294967295.

Note

 

To remove a profile from an interface, use the no ip igmp filter profile number interface configuration command.

Step 5

end

Example:


Device(config-if)# end

Returns to privileged EXEC mode.

Step 6

show running-config

Example:


Device# show running-config

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Setting the Maximum Number of IGMP Groups

Follow these steps to set the maximum number of IGMP groups that a Layer 2 interface can join:

Before you begin

This restriction can be applied to Layer 2 ports only; you cannot set a maximum number of IGMP groups on routed ports or SVIs. You also can use this command on a logical EtherChannel interface but cannot use it on ports that belong to an EtherChannel port group.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface interface-id
  4. ip igmp max-groups number
  5. end
  6. show running-config interface interface-id
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet0/2

Specifies the interface to be configured, and enters interface configuration mode. The interface can be a Layer 2 port that does not belong to an EtherChannel group or a EtherChannel interface.

Step 4

ip igmp max-groups number

Example:


Device(config-if)# ip igmp max-groups 20

Sets the maximum number of IGMP groups that the interface can join. The range is 0 to 4294967294. The default is to have no maximum set.

Note

 

To remove the maximum group limitation and return to the default of no maximum, use the no ip igmp max-groups interface configuration command.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show running-config interface interface-id

Example:


Device# interface gigabitethernet0/1

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Configuring the IGMP Throttling Action

After you set the maximum number of IGMP groups that a Layer 2 interface can join, you can configure an interface to replace the existing group with the new group for which the IGMP report was received.

Follow these steps to configure the throttling action when the maximum number of entries is in the forwarding table:

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface interface-id
  4. ip igmp max-groups action {deny | replace}
  5. end
  6. show running-config interface interface-id
  7. copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet0/1

Specifies the physical interface to be configured, and enters interface configuration mode. The interface can be a Layer 2 port that does not belong to an EtherChannel group or an EtherChannel interface. The interface cannot be a trunk port.

Step 4

ip igmp max-groups action {deny | replace}

Example:


Device(config-if)# ip igmp max-groups action replace

When an interface receives an IGMP report and the maximum number of entries is in the forwarding table, specifies the action that the interface takes:

  • deny —Drops the report. If you configure this throttling action, the entries that were previously in the forwarding table are not removed but are aged out. After these entries are aged out and the maximum number of entries is in the forwarding table, the device drops the next IGMP report received on the interface.

  • replace —Replaces the existing group with the new group for which the IGMP report was received. If you configure this throttling action, the entries that were previously in the forwarding table are removed. When the maximum number of entries is in the forwarding table, the device replaces a randomly selected entry with the received IGMP report.

To prevent the device from removing the forwarding-table entries, you can configure the IGMP throttling action before an interface adds entries to the forwarding table.

Note

 

To return to the default action of dropping the report, use the no ip igmp max-groups action interface configuration command.

Step 5

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Step 6

show running-config interface interface-id

Example:


Device# show running-config interface gigabitethernet0/1

Verifies your entries.

Step 7

copy running-config startup-config

Example:


Device# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Monitoring IGMP Snooping

Monitoring IGMP Snooping Information

You can display IGMP snooping information for dynamically learned and statically configured router ports and VLAN interfaces. You can also display MAC address multicast entries for a VLAN configured for IGMP snooping.

Table 5. Commands for Displaying IGMP Snooping Information

Command

Purpose

show ip igmp snooping [vlan vlan-id [detail] ]

Displays the snooping configuration information for all VLANs on the device or for a specified VLAN.

(Optional) Enter vlan vlan-id to display information for a single VLAN. The VLAN ID range is 1 to 1001 and 1006 to 4094.

show ip igmp snooping groups [count | vlan vlan-id]

Displays multicast table information for the device or about a specific parameter:

  • count —Displays the total number of entries for the specified command options instead of the actual entries.

  • vlan-id —The VLAN ID range is 1 to 1001 and 1006 to 4094.

show ip igmp snooping mrouter [vlan vlan-id]

Displays information on dynamically learned and manually configured multicast router interfaces.

Note

 

When you enable IGMP snooping, the device automatically learns the interface to which a multicast router is connected. These are dynamically learned interfaces.

(Optional) Enter the vlan vlan-id to display information for a particular VLAN.

show ip igmp snooping querier [vlan vlan-id] detail

Displays information about the IP address and receiving port of the most-recently received IGMP query message in the VLAN and the configuration and operational state of the IGMP snooping querier in the VLAN.

Monitoring IGMP Filtering

You can display IGMP profile characteristics, and you can display the IGMP profile and maximum group configuration for all interfaces on the device or for a specified interface.

Table 6. Commands for Displaying IGMP Filtering

Command

Purpose

show ip igmp profile [profile number]

Displays the specified IGMP profile or all the IGMP profiles defined on the device.

show running-config [interface interface-id]

Displays the configuration of the specified interface or the configuration of all interfaces on the device, including (if configured) the maximum number of IGMP groups to which an interface can belong and the IGMP profile applied to the interface.

Configuration Examples for IGMP Snooping

Example: Configuring IGMP Snooping Using CGMP Packets

This example shows how to configure IGMP snooping to use CGMP packets as the learning method: 
Device# configure terminal
Device(config)# ip igmp snooping vlan 1 mrouter learn cgmp
Device(config)# end

Example: Enabling a Static Connection to a Multicast Router

This example shows how to enable a static connection to a multicast router: 
Device configure terminal
Device ip igmp snooping vlan 200 mrouter interface gigabitethernet1/0/2
Device end

Example: Enabling IGMP Immediate Leave

This example shows how to enable IGMP Immediate Leave on VLAN 130: 
Device# configure terminal
Device(config)# ip igmp snooping vlan 130 immediate-leave
Device(config)# end

Example: Setting the IGMP Snooping Querier Source Address

This example shows how to set the IGMP snooping querier source address to 10.0.0.64: 
Device# configure terminal
Device(config)# ip igmp snooping querier 10.0.0.64
Device(config)# end

Example: Setting the IGMP Snooping Querier Maximum Response Time

This example shows how to set the IGMP snooping querier maximum response time to 25 seconds: 
Device# configure terminal
Device(config)# ip igmp snooping querier query-interval 25
Device(config)# end

Example: Setting the IGMP Snooping Querier Timeout

This example shows how to set the IGMP snooping querier timeout to 60 seconds: 
Device# configure terminal
Device(config)# ip igmp snooping querier timeout expiry 60
Device(config)# end

Example: Setting the IGMP Snooping Querier Feature

This example shows how to set the IGMP snooping querier feature to Version 2: 
Device# configure terminal
Device(config)# no ip igmp snooping querier version 2
Device(config)# end

Example: Configuring IGMP Profiles

This example shows how to create IGMP profile 4 allowing access to the single IP multicast address and how to verify the configuration. If the action was to deny (the default), it would not appear in the show ip igmp profile output display. 
Device(config)# ip igmp profile 4
Device(config-igmp-profile)# permit
Device(config-igmp-profile)# range 229.9.9.0
Device(config-igmp-profile)# end
Device# show ip igmp profile 4
IGMP Profile 4
    permit
    range 229.9.9.0 229.9.9.0

Example: Applying IGMP Profile

This example shows how to apply IGMP profile 4 to a port: 
Device(config)# interface gigabitethernet0/2
Device(config-if)# ip igmp filter 4
Device(config-if)# end

Example: Setting the Maximum Number of IGMP Groups

This example shows how to limit to 25 the number of IGMP groups that a port can join: 
Device(config)# interface gigabitethernet0/2
Device(config-if)# ip igmp max-groups 25
Device(config-if)# end

Additional References

Related Documents

Related Topic Document Title

For complete syntax and usage information for the commands used in this chapter.

IGMP Snooping and MVR Configuration Guide,Cisco IOS Release 15.2(2)E (Catalyst 2960-X Switch)

Standards and RFCs

Standard/RFC Title

RFC 1112

Host Extensions for IP Multicasting

RFC 2236

Internet Group Management Protocol, Version 2

MIBs

MIB MIBs Link

All the supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/support

Feature History and Information for IGMP Snooping

Release Modification

Cisco IOS Release 15.0(2)EXCisco IOS Release 15.2(5)E

This feature was introduced.