Catalyst 3550 Multilayer Switch Software Configuration Guide, Rel. 12.2(25)SEE - Configuring IGMP Snooping and MVR [Cisco Catalyst 3550 Series Switches]

Table Of Contents

Configuring IGMP Snooping and MVR

Understanding IGMP Snooping

IGMP Versions

Joining a Multicast Group

Leaving a Multicast Group

Immediate-Leave Processing

IGMP Configurable-Leave Timer

IGMP Report Suppression

Source-Only Networks

Configuring IGMP Snooping

Default IGMP Snooping Configuration

Enabling or Disabling IGMP Snooping

Setting the Snooping Method

Configuring a Multicast Router Port

Configuring a Host Statically to Join a Group

Enabling IGMP Immediate-Leave Processing

Configuring the IGMP Leave Timer

Configuring TCN-Related Commands

Controlling the Multicast Flooding Time After a TCN Event

Recovering from Flood Mode

Disabling Multicast Flooding During a TCN Event

Disabling IGMP Report Suppression

Configuring the Aging Time

Displaying IGMP Snooping Information

Understanding Multicast VLAN Registration

Using MVR in a Multicast Television Application

Configuring MVR

Default MVR Configuration

MVR Configuration Guidelines and Limitations

Configuring MVR Global Parameters

Configuring MVR Interfaces

Displaying MVR Information

Configuring IGMP Filtering and Throttling

Default IGMP Filtering and Throttling Configuration

Configuring IGMP Profiles

Applying IGMP Profiles

Setting the Maximum Number of IGMP Groups

Configuring the IGMP Throttling Action

Displaying IGMP Filtering and Throttling Configuration

Configuring IGMP Snooping and MVR

This chapter describes how to configure Internet Group Management Protocol (IGMP) snooping on your Catalyst 3550 switch, including an application of local IGMP snooping, Multicast VLAN Registration (MVR). It also includes procedures for controlling multicast group membership by using IGMP filtering and procedures for configuring the IGMP throttling action.

Note For complete syntax and usage information for the commands used in this chapter, see the switch command reference for this release and the "IP Multicast Routing Commands" section in the Cisco IOS IP Command Reference, Volume 3 of 3:Multicast, Release 12.2.

This chapter consists of these sections:

•Understanding IGMP Snooping

•Configuring IGMP Snooping

•Displaying IGMP Snooping Information

•Understanding Multicast VLAN Registration

•Configuring MVR

•Displaying MVR Information

•Configuring IGMP Filtering and Throttling

•Displaying IGMP Filtering and Throttling Configuration

Note For MAC addresses that map to IP multicast groups, you can either manage them through features such as IGMP snooping and MVR, or you can use static MAC addresses. However, you cannot use both methods simultaneously. Therefore, before using IGMP snooping or MVR, you should remove all statically configured MAC addresses that map to IP multicast groups.

Understanding IGMP Snooping

Layer 2 switches 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 switch to snoop on the IGMP transmissions between the host and the router and to keep track of multicast groups and member ports. When the switch receives an IGMP report from a host for a particular multicast group, the switch 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 (which could be a Catalyst 3550 switch with the enhanced multilayer software image) 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 switch forwards only one join request per IP multicast group to the multicast router. It creates one entry per VLAN in the Layer 2 forwarding table for each MAC group from which it receives an IGMP join request.

Layer 2 multicast groups learned through IGMP snooping are dynamic. However, you can statically configure MAC multicast groups by using the ip igmp snooping vlan static 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.

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 characteristics of IGMP snooping on the switch:

•IGMP Versions

•Joining a Multicast Group

•Leaving a Multicast Group

•Immediate-Leave Processing

•IGMP Configurable-Leave Timer

•IGMP Report Suppression

•Source-Only Networks

IGMP Versions

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

Note The switch supports IGMPv3 snooping based only on the destination multicast MAC address. It does not support snooping based on the source MAC address or on proxy reports.

An IGMPv3 switch supports Basic IGMPv3 Snooping Support (BISS), which includes support for the snooping features on IGMPv1 and IGMPv2 switches and for IGMPv3 membership report messages. BISS constrains the flooding of multicast traffic when your network includes IGMPv3 hosts. It constrains traffic to approximately the same set of ports as the IGMP snooping feature on IGMPv2 or IGMPv1 hosts.

Note IGMPv3 join and leave messages are not supported on switches running IGMP filtering or MVR.

An IGMPv3 switch can receive messages from and forward messages to a device running the Source Specific Multicast (SSM) feature. For more information, see the "Configuring IP Multicast Layer 3 Switching" chapter in the Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, Cisco IOS Release 12.1(12c)EW at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat4000/12_1_12/config/mcastmls.htm

Joining a Multicast Group

When a host connected to the switch wants to join an IP multicast group, it sends an unsolicited IGMP join message, specifying the IP multicast group to join. Alternatively, when the switch receives a general query from the router, it forwards the query to all ports in the VLAN. Hosts wanting to join the multicast group respond by sending a join message to the switch. The switch 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. See Figure 21-1.

Figure 21-1 Initial IGMP Join Message

Router A sends a general query to the switch, which forwards the query to ports 2 through 5, all 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 with the equivalent MAC destination address of 0x0100.5E01.0203. When the CPU receives the IGMP report multicast by Host 1, the CPU uses the information in the IGMP report to set up a forwarding-table entry, as shown in Table 21-1, that includes the port numbers of Host 1, the router, and the switch internal CPU.

Table 21-1 IGMP Snooping Forwarding Table

Destination Address

Type of Packet

Ports

0100.5exx.xxxx

IGMP

0

0100.5e01.0203

!IGMP

1, 2

Note that the switch hardware can distinguish IGMP information packets from other packets for the multicast group.

•The first entry in the table tells the switching engine to send IGMP packets to only the switch CPU. This prevents the CPU from becoming overloaded with multicast frames.

•The second entry tells the switching engine to send frames addressed to the 0x0100.5E01.0203 multicast MAC address that are not IGMP packets (!IGMP) to the router and to the host that has joined the group.

If another host (for example, Host 4) sends an unsolicited IGMP join message for the same group (Figure 21-2), the CPU receives that message and adds the port number of Host 4 to the forwarding table as shown in Table 21-2. Note that because the forwarding table directs IGMP messages only to the CPU, the message is not flooded to other ports on the switch. Any known multicast traffic is forwarded to the group and not to the CPU.

Figure 21-2 Second Host Joining a Multicast Group

Table 21-2 Updated IGMP Snooping Forwarding Table

Destination Address

Type of Packet

Ports

0100.5exx.xxxx

IGMP

0

0100.5e01.0203

!IGMP

1, 2, 5

Leaving a Multicast Group

The router sends periodic multicast general queries and the switch forwards these queries through all ports in the VLAN. Interested hosts respond to the queries. If at least one host in the VLAN wishes to receive multicast traffic, the router continues forwarding the multicast traffic to the VLAN. The switch forwards multicast group traffic to only those hosts listed in the forwarding table for that Layer 2 multicast group.

When hosts want to leave a multicast group, they can either silently leave, or they can send a leave message. When the switch receives a leave message from a host, it sends a group-specific query to determine if any other devices connected to that interface are interested in traffic for the specific multicast group. The switch 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 Processing

Immediate Leave is only supported with IGMP version 2 hosts.

The switch uses IGMP snooping Immediate-Leave processing to remove from the forwarding table an interface that sends a leave message without the switch 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 processing ensures optimal bandwidth management for all hosts on a switched network, even when multiple multicast groups are simultaneously in use.

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

IGMP Configurable-Leave Timer

In Cisco IOS Release 12.2(25)SEA and earlier, the IGMP snooping leave time was fixed at 5 seconds. If membership reports were not received by the switch before the query response time of the query expired, a port was removed from the multicast group membership. However, some applications require a leave latency of less than 5 seconds.

In Cisco IOS Release 12.2(25)SEB and later, you can configure the time that the switch 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 5000 milliseconds. The timer can be set either globally or on a per-VLAN basis. The VLAN configuration of the leave time overrides the global configuration.

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 switch uses IGMP report suppression to forward only one IGMP report per multicast router query to multicast devices. When IGMP router suppression is enabled (the default), the switch sends the first IGMP report from all hosts for a group to all the multicast routers. The switch 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 switch 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 switch 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.

Source-Only Networks

In a source-only network, switch ports are connected to multicast source ports and multicast router ports. The switch ports are not connected to hosts that send IGMP join or leave messages.

The switch learns about IP multicast groups that alias with reserved, destination, multicast IP addresses (224.0.0.x) from the IP multicast data stream by using the source-only learning method. The switch forwards traffic that aliases with these multicast addresses only to the multicast router ports.

The default learning method for traffic that aliases with reserved, destination, multicast IP addresses is IP multicast-source-only learning.Traffic that does not alias with these multicast addresses is forwarded to both the multicast source ports and multicast router ports. You cannot disable IP multicast-source-only learning for the traffic with reserved, destination, multicast IP addresses.

By default, the switch ages out forwarding-table entries that were learned by the source-only learning method and that are not in use. If the aging time is too long or is disabled, the forwarding table is filled with unused entries that the switch learned by using source-only learning or by using the IGMP join messages. When the switch receives traffic for new IP multicast groups, it floods the packet to all ports in the same VLAN. This unnecessary flooding can impact switch performance.

If aging is disabled and you want to delete multicast addresses that the switch learned by using source-only learning, re-enable aging of the forwarding-table entries. The switch can now age out the multicast addresses that were learned by the source-only learning method and are not in use.

Configuring IGMP Snooping

IGMP snooping allows switches to examine IGMP packets and make forwarding decisions based on their content. To enable IGMP snooping on the switch to discover external multicast routers, the Layer 3 interfaces on the routers in the VLAN must already have been configured for multicast routing. For more information, see Chapter 35, "Configuring IP Multicast Routing."

These sections describe how to configure IGMP snooping:

•Default IGMP Snooping Configuration

•Enabling or Disabling IGMP Snooping

•Setting the Snooping Method

•Configuring a Multicast Router Port

•Configuring a Host Statically to Join a Group

•Enabling IGMP Immediate-Leave Processing

•Configuring the IGMP Leave Timer

•Configuring TCN-Related Commands

•Disabling IGMP Report Suppression

•Configuring the Aging Time

•Displaying IGMP Snooping Information

Default IGMP Snooping Configuration

Table 21-3 shows the default IGMP snooping configuration.

Table 21-3 Default IGMP Snooping Configuration

Feature

Default Setting

IGMP snooping

Enabled globally and per VLAN.

Multicast routers

None configured.

Multicast router learning (snooping) method

PIM-DVMRP.

IGMP snooping Immediate Leave

Disabled.

Static groups

None configured.

Topology change notification flood query count

2

Topology change notification query solicitation

Disabled

Aging forward-table entries (for traffic that aliases with reserved, destination, multicast IP addresses)

Enabled. The default is 600 seconds (10 minutes).

IGMP report suppression

Enabled.

Enabling or Disabling IGMP Snooping

By default, IGMP snooping is globally enabled on the switch. When globally enabled or disabled, it is also enabled or disabled in all existing VLAN interfaces. IGMP snooping is by default enabled on all VLANs, but can be enabled and disabled on a per-VLAN basis. After you configure the VLAN interface for multicast routing, no configuration is needed for the switch to dynamically access external multicast routers by using IGMP snooping.

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.

Beginning in privileged EXEC mode, follow these steps to globally enable IGMP snooping on the switch:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

ip igmp snooping

Globally enable IGMP snooping in all existing VLAN interfaces.

Step 3

end

Return to privileged EXEC mode.

Step 4

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

Beginning in privileged EXEC mode, follow these steps to enable IGMP snooping on a VLAN interface:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

ip igmp snooping vlan vlan-id

Enable IGMP snooping on the VLAN interface.

Step 3

end

Return to privileged EXEC mode.

Step 4

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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.

Setting the Snooping Method

Multicast-capable router ports are added to the forwarding table for every Layer 2 multicast entry. The switch learns of such 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 with the ip igmp snooping mrouter global configuration command

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 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.

Note 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. For more information, see Chapter 35, "Configuring IP Multicast Routing."

Beginning in privileged EXEC mode, follow these steps to alter the method in which a VLAN interface dynamically accesses a multicast router:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

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

Enable IGMP snooping on a VLAN. The VLAN ID range is 1 to 4094.

Specify the multicast router learning method:

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

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

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping

Verify the configuration.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

This example shows how to configure IGMP snooping to use CGMP packets as the learning method:
Switch# configure terminal
Switch(config)# ip igmp snooping vlan 1 mrouter learn cgmp
Switch(config)# end       
To return to the default learning method, use the no ip igmp snooping vlan vlan-id mrouter learn cgmp global configuration command.

Configuring a Multicast Router Port

To add a multicast router port (add a static connection to a multicast router), use the ip igmp snooping vlan mrouter global configuration command on the switch.

Note Static connections to multicast routers are supported only on switch ports.

Beginning in privileged EXEC mode, follow these steps to enable a static connection to a multicast router:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

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

Specify the multicast router VLAN ID and specify the interface to the multicast router. The VLAN ID range is 1 to 4094.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping mrouter [vlan vlan-id]

Verify that IGMP snooping is enabled on the VLAN interface.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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.

This example shows how to enable a static connection to a multicast router and verify the configuration:
Switch# configure terminal
Switch(config)# ip igmp snooping vlan 200 mrouter interface gigabitethernet0/1
Switch(config)# end
Configuring a Host Statically to Join a Group

Hosts or Layer 2 ports normally join multicast groups dynamically, but you can also statically configure a host on an interface.

Beginning in privileged EXEC mode, follow these steps to add a Layer 2 port as a member of a multicast group:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode

Step 2

ip igmp snooping vlan vlan-id static mac-address interface interface-id

Statically configure a Layer 2 port as a member of a multicast group:

•vlan-id is the multicast group VLAN ID.

•mac-address is the group MAC address.

•interface-id is the member port.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping groups

Verify the member port and the IP address.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To remove the Layer 2 port from the multicast group, use the no ip igmp snooping vlan vlan-id static mac-address interface interface-id global configuration command.

This example shows how to statically configure a host on an interface and verify the configuration:
Switch# configure terminal
Switch(config)# ip igmp snooping vlan 1 static 0100.5e00.0203 interface gigabitethernet0/1
Switch(config)# end
Enabling IGMP Immediate-Leave Processing

When you enable IGMP Immediate-Leave processing, the switch 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 with only IGMP version 2 hosts.

Beginning in privileged EXEC mode, follow these steps to enable IGMP Immediate-Leave processing:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode

Step 2

ip igmp snooping vlan vlan-id immediate-leave

Enable IGMP Immediate-Leave processing on the VLAN interface.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping vlan vlan-id

Verify that Immediate Leave is enabled on the VLAN.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

This example shows how to enable IGMP immediate-leave processing on VLAN 130:
Switch# configure terminal
Switch(config)# ip igmp snooping vlan 130 immediate-leave
Switch(config)# end
Configuring the IGMP Leave Timer

Follows these guidelines when configuring the IGMP leave timer:

•You can configure the leave time globally or on a per-VLAN basis.

•Configuring the leave time on a VLAN overrides the global setting.

•The default leave time is 1000 milliseconds.

•The IGMP configurable leave time is only supported on hosts running IGMP Version 2.

•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.

Beginning in privileged EXEC mode, follow these steps to enable the IGMP configurable-leave timer:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

ip igmp snooping last-member-query-interval time

Configure the IGMP leave timer globally. The range is 100 to 5000 milliseconds.

Step 3

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

(Optional) Configure the IGMP leave time on the VLAN interface. The range is 100 to 5000 milliseconds.

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

Step 4

end

Return to privileged EXEC mode.

Step 5

show ip igmp snooping

(Optional) Display the configured IGMP leave time.

Step 6

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Use the no ip igmp snooping last-member-query-interval global configuration command to globally reset the IGMP leave timer to the default setting (1000 milliseconds).

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

Configuring TCN-Related Commands

These sections describe how to control flooded multicast traffic during a TCN event:

•Controlling the Multicast Flooding Time After a TCN Event

•Recovering from Flood Mode

•Disabling Multicast Flooding During a TCN Event

Controlling the Multicast Flooding Time After a TCN Event

You can control the time that multicast traffic is flooded after a TCN event by using the ip igmp snooping tcn flood query count global configuration command. This command configures the number of general queries for which multicast data traffic is flooded after a TCN event. Some examples of TCN events are when the client changed its location and the receiver is on same port that was blocked but is now forwarding, and when a port went down without sending a leave message.

If you set the TCN flood query count to 1 by using the ip igmp snooping tcn flood query count command, the flooding stops after receiving one general query. If you set the count to 7, the flooding of multicast traffic due to the TCN event lasts until seven general queries are received. Groups are relearned based on the general queries received during the TCN event.

Beginning in privileged EXEC mode, follow these steps to configure the TCN flood query count:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

ip igmp snooping tcn flood query count count

Specify the number of IGMP general queries for which the multicast traffic is flooded. The range is 1 to 10. By default, the flooding query count is 2.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping

Verify the TCN settings.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

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, when you enable the ip igmp snooping tcn query solicit global configuration command, the switch sends the global leave message whether or not it is the spanning-tree root. 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 switch is the spanning-tree root regardless of this configuration command. By default, query solicitation is disabled.

Beginning in privileged EXEC mode, follow these steps to enable the switch to send the global leave message whether or not it is the spanning-tree root:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

ip igmp snooping tcn query solicit

Send 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.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping

Verify the TCN settings.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

Disabling Multicast Flooding During a TCN Event

When the switch receives a TCN, multicast traffic is flooded to all the ports until two general queries are received. If the switch 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. You can use the ip igmp snooping tcn flood interface configuration command to control this behavior.

Beginning in privileged EXEC mode, follow these steps to disable multicast flooding on an interface:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

interface interface-id

Specify the interface to be configured, and enter interface configuration mode.

Step 3

no ip igmp snooping tcn flood

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

By default, multicast flooding is enabled on an interface.

Step 4

exit

Return to privileged EXEC mode.

Step 5

show ip igmp snooping

Verify the TCN settings.

Step 6

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

Disabling IGMP Report Suppression

IGMP report suppression is enabled by default. When it is enabled, the switch forwards only one IGMP report per multicast router query. When report suppression is disabled, all IGMP reports are forwarded to the multicast routers.

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.

Beginning in privileged EXEC mode, follow these steps to disable IGMP report suppression:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

no ip igmp snooping report-suppression

Disable IGMP report suppression.

Step 3

end

Return to privileged EXEC mode.

Step 4

show ip igmp snooping

Verify that IGMP report suppression is disabled.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

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

Configuring the Aging Time

You can set the aging time for forwarding-table entries that the switch learns by using the IP multicast-source-only learning method.

Beginning in privileged EXEC mode, follow these steps to configure the aging time:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode

Step 2

ip igmp snooping source-only learning age-timer time

Set the aging time. The range is 0 to 2880 seconds. The default is 600 seconds (10 minutes).

Step 3

end

Return to privileged EXEC mode.

Step 4

show running-config | include source-only-learning

Verify the aging time.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To disable the aging of the forwarding table entries, enter the ip igmp snooping source-only-learning age-timer 0 global configuration command.

Displaying 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.

To display IGMP snooping information, use one or more of the privileged EXEC commands in Table 21-4.

Table 21-4 Commands for Displaying IGMP Snooping Information

Command

Purpose

show ip igmp snooping [vlan vlan-id]

Display the snooping configuration information for all VLANs on the switch or for a specified VLAN.

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

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

Display multicast table information for the switch, for a multicast VLAN, or about a specific parameter:

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

•ip_address—Display information for multicast group with the specified group IP address.

show ip igmp snooping mrouter [vlan vlan-id]

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

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

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

show mac address-table multicast [vlan vlan-id] [user | igmp-snooping] [count]

Display the Layer 2 MAC address table entries for a VLAN. The keywords are all optional and limit the display as shown:

•vlan vlan-id—Displays only the specified multicast group VLAN.

•user—Displays only the user-configured multicast entries.

•igmp-snooping—Displays only entries learned through IGMP snooping.

•count—Displays only the total number of entries for the selected criteria, not the actual entries.

For more information about the keywords and options in these commands, see the command reference for this release.

For examples of output from the commands in Table 21-4, see the command reference for this release.

Understanding Multicast VLAN Registration

Multicast VLAN Registration (MVR) is designed for applications using wide-scale deployment of multicast traffic across an Ethernet ring-based service provider network (for example, the broadcast of multiple television channels over a service-provider network). MVR allows a subscriber on a port to subscribe and unsubscribe to a multicast stream on the network-wide multicast VLAN. It allows the single multicast VLAN to be shared in the network while subscribers remain in separate VLANs. MVR provides the ability to continuously send multicast streams in the multicast VLAN, but to isolate the streams from the subscriber VLANs for bandwidth and security reasons.

MVR assumes that subscriber ports subscribe and unsubscribe (join and leave) these multicast streams by sending out IGMP join and leave messages. These messages can originate from an IGMP version-2-compatible host with an Ethernet connection. Although MVR operates on the underlying mechanism of IGMP snooping, the two features operate independently of each other. One can be enabled or disabled without affecting the behavior of the other feature. However, if IGMP snooping and MVR are both enabled, MVR reacts only to join and leave messages from multicast groups configured under MVR. Join and leave messages from all other multicast groups are managed by IGMP snooping.

The switch CPU identifies the MVR IP multicast streams and their associated MAC addresses in the switch forwarding table, intercepts the IGMP messages, and modifies the forwarding table to include or remove the subscriber as a receiver of the multicast stream, even though the receivers might be in a different VLAN from the source. This forwarding behavior selectively allows traffic to cross between different VLANs.

The switch has these modes of MVR operation: dynamic and compatible.

•When operating in MVR dynamic mode, the switch performs standard IGMP snooping. IGMP information packets are sent to the switch CPU, but multicast data packets are not sent to the CPU. Dynamic mode allows the multicast router to run normally because the switch sends the IGMP join messages to the router, and the router forwards multicast streams for a particular group to an interface only if it has received a join message from the interface for the group. Receiver ports are treated as members of the multicast VLAN for MVR multicast control and data traffic. IGMP reports for MVR groups are sent out source ports in the multicast VLAN.

•When in MVR compatible mode, MVR on the Catalyst 3550 switch interoperates with MVR on Catalyst 3500 XL and Catalyst 2900 XL switches. It works the same as dynamic mode for all multicast data packets and IGMP query and leave packets. However, received IGMP report packets for MVR groups are not sent out on the multicast VLAN source ports. In contrast to dynamic mode, the switch does not send join messages to the router. The router must be statically configured for the interface to receive the multicast stream. Therefore, in this mode, MVR does not support dynamic membership joins on source ports.

Note IGMPv3 join and leave messages are not supported on switches running MVR.

Using MVR in a Multicast Television Application

In a multicast television application, a PC or a television with a set-top box can receive the multicast stream. Multiple set-top boxes or PCs can be connected to one subscriber port, which is a switch port configured as an MVR receiver port. Figure 21-3 is an example configuration. DHCP assigns an IP address to the set-top box or the PC. When a subscriber selects a channel, the set-top box or PC sends an IGMP report to Switch A to join the appropriate multicast. If the IGMP report matches one of the configured multicast MAC addresses, the switch CPU modifies the hardware address table to include this receiver port and VLAN as a forwarding destination of the specified multicast stream when it is received from the multicast VLAN. Uplink ports that send and receive multicast data to and from the multicast VLAN are called MVR source ports.

When a subscriber changes channels or turns off the television, the set-top box sends an IGMP leave message for the multicast stream. The switch CPU sends an IGMP group-specific query through the receiver port VLAN. If there is another set-top box in the VLAN still subscribing to this group, that set-top box must respond within the maximum response time. If the CPU does not receive a response, it eliminates the receiver port as a forwarding destination for this group.

Without Immediate Leave, when the switch receives an IGMP leave message from a subscriber on a receiver port, it sends out an IGMP query on that port and waits for IGMP group membership reports. If no reports are received in a configured time period, the receiver port is removed from multicast group membership. With Immediate Leave, an IGMP query is not sent from the receiver port on which the IGMP leave was received. As soon as the leave message is received, the receiver port is removed from multicast group membership, which speeds up leave latency. Enable the Immediate Leave feature only on receiver ports to which a single receiver device is connected.

Figure 21-3 Multicast VLAN Registration Example

MVR eliminates the need to duplicate television-channel multicast traffic for subscribers in each VLAN. Multicast traffic for all channels is only sent around the VLAN trunk once—only on the multicast VLAN. Although the IGMP leave and join message in the VLAN to which the subscriber port is assigned. These messages dynamically register for streams of multicast traffic in the multicast VLAN on the Layer 3 device. The access layer switch (Switch A) modifies the forwarding behavior to allow the traffic to be forwarded from the multicast VLAN to the subscriber port in a different VLAN, selectively allowing traffic to cross between two VLANs.

IGMP reports are sent to the same MAC addresses as the multicast data. The Switch A CPU must capture all IGMP join and leave messages from receiver ports and forward them to the multicast VLAN of the source (uplink) port.

Configuring MVR

These sections include basic MVR configuration information:

•Default MVR Configuration

•MVR Configuration Guidelines and Limitations

•Configuring MVR Global Parameters

•Configuring MVR Interfaces

Default MVR Configuration

Table 21-5 shows the default MVR configuration.

Table 21-5 Default MVR Configuration

Feature

Default Setting

MVR

Disabled globally and per interface

Multicast addresses

None configured

Query response time

0.5 second

Multicast VLAN

VLAN 1

Mode

Compatible

Interface (per port) default

Neither a receiver nor a source port

Immediate Leave

Disabled on all ports

MVR Configuration Guidelines and Limitations

Follow these guidelines when configuring MVR:

•Receiver ports cannot be trunk ports. Receiver ports on a switch can be in different VLANs, but should not belong to the multicast VLAN.

•The maximum number of multicast entries that can be configured on a switch (that is, the maximum number of television channels that can be received) is 256.

•Each channel is one multicast stream destined for a unique IP multicast address. These IP addresses cannot alias between themselves or with the reserved IP multicast addresses (in the range 224.0.0.xxx).

•Multicast routing and MVR cannot coexist on a switch. If you enable multicast routing and a multicast routing protocol while MVR is enabled, MVR is disabled, and you receive a warning message. If you try to enable MVR while multicast routing and a multicast routing protocol are enabled, the operation to enable MVR is cancelled, and you receive an error message.

•MVR does not support IGMPv3 messages.

Note For complete syntax and usage information for the commands used in this section, see the command reference for this release.

Configuring MVR Global Parameters

You do not need to set the optional MVR parameters if you choose to use the default settings. If you do want to change the default parameters (except for the MVR VLAN), you must first enable MVR.

Beginning in privileged EXEC mode, follow these steps to configure MVR parameters:

Command

Purpose

Step 1

configure terminal

Enter global configuration mode.

Step 2

mvr

Enable MVR on the switch.

Step 3

mvr group ip-address [count]

Configure an IP multicast address on the switch or use the count parameter to configure a contiguous series of MVR group addresses (the range for count is 1 to 256; the default is 1). Any multicast data sent to this address is sent to all source ports on the switch and all receiver ports that have elected to receive data on that multicast address. Each multicast address would correspond to one television channel.

Note Each IP address translates to a multicast 48-bit MAC address. If an IP address being configured translates (aliases) to a previously configured MAC address or to any reserved multicast MAC addresses, the command fails.

Step 4

mvr querytime value

(Optional) Define the maximum time to wait for IGMP report memberships on a receiver port before removing the port from multicast group membership. The value is in units of tenths of a second. The range is from 1 to 100 and the default is 5 tenths or one-half second.

Step 5

mvr vlan vlan-id

(Optional) Specify the VLAN in which multicast data is received; all source ports must belong to this VLAN. The VLAN ID range is 1 to 4094. The default is VLAN 1.

Step 6

mvr mode {dynamic | compatible}

(Optional) Specify the MVR mode of operation:

•dynamic—Allows dynamic MVR membership on source ports.

•compatible—Is compatible with Catalyst 3500 XL and Catalyst 2900 XL switches and does not support IGMP dynamic joins on source ports.

The default is compatible mode.

Step 7

end

Return to privileged EXEC mode.

Step 8

show mvr

or

show mvr members

Verify the configuration.

Step 9