You can configure the controller as a member of a multicast group and discover multicast reachability in a network. If all the multicast-capable routers and multilayer controllers that you administer are members of a multicast group, pinging that group causes all of these devices to respond. The devices respond to ICMP echo-request packets addressed to a group of which they are members. Another example is the multicast trace-route tools provided in the software.

Caution

Performing this procedure might impact the CPU performance because the CPU will receive all data traffic for the group address.

This procedure is optional.

The controller sends IGMP host-query messages to find which multicast groups have members on attached local networks. The controller then forwards to these group members all packets addressed to the multicast group. You can place a filter on each interface to restrict the multicast groups that hosts on the subnet serviced by the interface can join.

To limit the number of joins on the interface, configure the port for the filter which associates with the IGMP profile.

This procedure is optional.

The controller periodically sends IGMP host-query messages to discover which multicast groups are present on attached networks. These messages are sent to the all-hosts multicast group (224.0.0.1) with a time-to-live (TTL) of 1. The controller sends host-query messages to refresh its knowledge of memberships present on the network. If, after some number of queries, the software discovers that no local hosts are members of a multicast group, the software stops forwarding multicast packets to the local network from remote origins for that group and sends a prune message upstream toward the source.

The controller elects a PIM designated router (DR) for the LAN (subnet). The DR is the router or multilayer controller with the highest IP address for IGMPv2. For IGMPv1, the DR is elected according to the multicast routing protocol that runs on the LAN. The designated router is responsible for sending IGMP host-query messages to all hosts on the LAN. In sparse mode, the designated router also sends PIM register and PIM join messages toward the RP router.

This procedure is optional.

If you are using IGMPv2, you can specify the period of time before the controller takes over as the querier for the interface. By default, the controller waits twice the query interval period controlled by the ip igmp query-interval interface configuration command. After that time, if the controller has received no queries, it becomes the querier.

This procedure is optional.

If you are using IGMPv2, you can change the maximum query response time advertised in IGMP queries. The maximum query response time enables the controller to quickly detect that there are no more directly connected group members on a LAN. Decreasing the value enables the controller to prune groups faster.

This procedure is optional.

At various times, either there is not a group member on a network segment or a host that cannot report its group membership by using IGMP. However, you may want multicast traffic to be sent to that network segment. The following commands are used to pull multicast traffic down to a network segment:

• ip igmp join-group—The controller accepts the multicast packets in addition to forwarding them. Accepting the multicast packets prevents the controller from fast switching.
• ip igmp static-group—The controller does not accept the packets itself, but only forwards them. This method enables fast switching. The outgoing interface appears in the IGMP cache, but the controller itself is not a member, as evidenced by lack of an L (local) flag in the multicast route entry.

This procedure is optional.

To configure an IGMP profile, use the ip igmp profile global configuration command with a profile number to create an IGMP profile and to enter IGMP profile configuration mode. From this mode, you can specify the parameters of the IGMP profile to be used for filtering IGMP join requests from a port. 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 controller to have no IGMP profiles configured. When a profile is configured, if neither the permit nor deny keyword is included, the default is to deny access to the range of IP addresses.

To control access as defined in an IGMP profile, use the ip igmp filter interface configuration command 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.

You can set the maximum number of IGMP groups that a Layer 2 interface can join by using the ip igmp max-groups interface configuration command. Use the no form of this command to set the maximum back to the default, which is no limit.

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.

Beginning in privileged EXEC mode, follow these steps to set the maximum number of IGMP groups in the forwarding table:

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 by using the ip igmp max-groups action replace interface configuration command. Use the no form of this command to return to the default, which is to drop the IGMP join report.

Follow these guidelines when configuring the IGMP throttling action:

• This restriction can be applied only to Layer 2 ports. You can use this 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.
  • If you configure the throttling action as deny, 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 controller drops the next IGMP report received on the interface.
  • If you configure the throttling action as replace, the entries that were previously in the forwarding table are removed. When the maximum number of entries is in the forwarding table, the controller replaces a randomly selected entry with the received IGMP report. To prevent the controller from removing the forwarding-table entries, you can configure the IGMP throttling action before an interface adds entries to the forwarding table.

By default, IGMP snooping is globally enabled on the controller. 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.

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.

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

• Snooping on IGMP queries
• Statically connecting to a multicast router port using the ip igmp snooping mrouter global configuration command

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

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 controller.

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

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

When you enable IGMP Immediate Leave, the controller immediately removes a port when it detects an IGMP Version 2 leave message on that port. You should only use the Immediate-Leave feature 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 controller.

Follow 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. IGMP version 2 is the default version for the controller.
• 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.

Use the following procedure to configure the IGMP robustness variable on the controller.

The robustness variable is the integer used by IGMP snooping during calculations for IGMP messages. The robustness variable provides fine tuning to allow for expected packet loss.

To configure the number of times the controller sends IGMP group-specific or group-source-specific (with IGMP version 3) query messages in response to receiving a group-specific or group-source-specific leave message, use this command.

You can control the time that multicast traffic is flooded after a topology change notification (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 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.

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 controller 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 controller is the spanning-tree root regardless of this configuration command. By default, query solicitation is disabled.

When the controller receives a TCN, multicast traffic is flooded to all the ports until 2 general queries are received. If the controller 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 operation function.

Follow 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 controller virtual interface (SVI) IP address (if one exists). If there is no SVI IP address, the controller uses the first available IP address configured on the controller. 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 controller.
• 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 under these conditions:
  • IGMP snooping is disabled in the VLAN.
  • PIM is enabled on the SVI of the corresponding VLAN.

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.

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

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.

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

This example shows how to enable the controller to join multicast group 255.2.2.2:

          
          
Controller(config)# interface gigabitethernet1/0/1
Controller(config-if)# ip igmp join-group 255.2.2.2
Controller(config-if)#

To limit the number of joins on the interface, configure the port for filter which associates with the IGMP profile.

Controller# configure terminal
Controller(config)# ip igmp profile 10
Controller(config-igmp-profile)# ?

IGMP profile configuration commands:
deny matching addresses are denied
exit Exit from igmp profile configuration mode
no Negate a command or set its defaults
permit matching addresses are permitted
range add a range to the set

Controller(config-igmp-profile)# range 172.16.5.1
Controller(config-igmp-profile)# exit
Controller(config)#
Controller(config)# interface gigabitEthernet 2/0/10
Controller(config-if)# ip igmp filter 10

This example shows how to enable a static connection to a multicast router:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping vlan 200 mrouter interface gigabitethernet1/0/2
Controller(config)# end

This example shows how to statically configure a host on a port:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping vlan 105 static 224.2.4.12 interface gigabitethernet1/0/1
Controller(config)# end

This example shows how to enable IGMP Immediate Leave on VLAN 130:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping vlan 130 immediate-leave
Controller(config)# end

This example shows how to set the IGMP snooping querier source address to 10.0.0.64:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping querier 10.0.0.64
Controller(config)# end

This example shows how to set the IGMP snooping querier maximum response time to 25 seconds:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping querier query-interval 25
Controller(config)# end

This example shows how to set the IGMP snooping querier timeout to 60 seconds:

          
          
Controller# configure terminal
Controller(config)# ip igmp snooping querier timer expiry 60
Controller(config)# end

This example shows how to set the IGMP snooping querier feature to Version 2:

          
          
Controller# configure terminal
Controller(config)# no ip igmp snooping querier version 2
Controller(config)# end

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.

          
          
Controller(config)# ip igmp profile 4
Controller(config-igmp-profile)# permit
Controller(config-igmp-profile)# range 229.9.9.0
Controller(config-igmp-profile)# end
Controller# show ip igmp profile 4
IGMP Profile 4
    permit
    range 229.9.9.0 229.9.9.0

This example shows how to apply IGMP profile 4 to a port:

          
          
Controller(config)# interface gigabitethernet1/0/2
Controller(config-if)# ip igmp filter 4
Controller(config-if)# end

This example shows how to limit to 25 the number of IGMP groups that a port can join:

          
          
Controller(config)# interface gigabitethernet1/0/2
Controller(config-if)# ip igmp max-groups 25
Controller(config-if)# end

This example shows how to configure an interface on the controller as a routed port. This configuration is required on the interface for several IP multicast routing configuration procedures that require running the no switchport command.

Controller configure terminal
Controller(config)#  interface GigabitEthernet1/0/9
Controller(config-if)# description interface to be use as routed port
Controller(config-if)# no switchport
Controller(config-if)# ip address 20.20.20.1 255.255.255.0
Controller(config-if)# ip pim sparse-dense-mode
Controller(config-if)# ip igmp join-group 224.1.2.3 source 15.15.15.2
Controller(config-if)# end
Controller# configure terminal
Controller# show run interface gigabitEthernet 1/0/9

Current configuration : 166 bytes
!
interface GigabitEthernet1/0/9
 no switchport
 ip address 20.20.20.1 255.255.255.0
 ip pim sparse-dense-mode
 ip igmp static-group 224.1.2.3 source 15.15.15.2
end

This example shows how to configure an interface on the controller as an SVI. This configuration is required on the interface for several IP multicast routing configuration procedures that require running the no switchport command.

Controller(config)# interface vlan 150
Controller(config-if)# ip address 20.20.20.1 255.255.255.0
Controller(config-if)# ip pim sparse-dense-mode
Controller(config-if)# ip igmp join-group 224.1.2.3 source 15.15.15.2
Controller(config-if)# end
Controller# configure terminal
Controller(config)#  ip igmp snooping vlan 20 static 224.1.2.3 interface gigabitEthernet 1/0/9
Controller# show run interface vlan 150

Current configuration : 137 bytes
!
interface Vlan150
 ip address 20.20.20.1 255.255.255.0
 ip pim sparse-dense-mode
 ip igmp static-group 224.1.2.3 source 15.15.15.2
end