Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
Configuring IGMP
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Configuring IGMP

This chapter describes how to configure the Internet Group Management Protocol (IGMP) on Cisco NX-OS devices for IPv4 networks.

Information About IGMP

IGMP is an IPv4 protocol that a host uses to request multicast data for a particular group. Using the information obtained through IGMP, the software maintains a list of multicast group or channel memberships on a per-interface basis. The systems that receive these IGMP packets send multicast data that they receive for requested groups or channels out the network segment of the known receivers.

By default, the IGMP process is running. You cannot enable IGMP manually on an interface. IGMP is automatically enabled when you perform one of the following configuration tasks on an interface:

  • Enable PIM
  • Statically bind a local multicast group
  • Enable link-local group reports

IGMP Versions

The device supports IGMPv2 and IGMPv3, as well as IGMPv1 report reception.

By default, the software enables IGMPv2 when it starts the IGMP process. You can enable IGMPv3 on interfaces where you want its capabilities.

IGMPv3 includes the following key changes from IGMPv2:

  • Support for Source-Specific Multicast (SSM), which builds shortest path trees from each receiver to the source, through the following features:
    • Host messages that can specify both the group and the source.
    • The multicast state that is maintained for groups and sources, not just for groups as in IGMPv2.
  • Hosts no longer perform report suppression, which means that hosts always send IGMP membership reports when an IGMP query message is received.

For detailed information about IGMPv2, see RFC 2236.

For detailed information about IGMPv3, see RFC 3376.

IGMP Basics

The basic IGMP process of a router that discovers multicast hosts is shown in the Figure below. Hosts 1, 2, and 3 send unsolicited IGMP membership report messages to initiate receiving multicast data for a group or channel.

Figure 1. IGMPv1 and IGMPv2 Query-Response Process

In the Figure below, , router A, which is the IGMP designated querier on the subnet, sends query messages to the all-hosts multicast group at 224.0.0.1 periodically to discover whether any hosts want to receive multicast data. You can configure the group membership timeout value that the router uses to determine that no members of a group or source exist on the subnet. For more information about configuring the IGMP parameters, see Configuring IGMP Interface Parameters.

The software elects a router as the IGMP querier on a subnet if it has the lowest IP address. As long as a router continues to receive query messages from a router with a lower IP address, it resets a timer that is based on its querier timeout value. If the querier timer of a router expires, it becomes the designated querier. If that router later receives a host query message from a router with a lower IP address, it drops its role as the designated querier and sets its querier timer again.

In this Figure, host 1’s membership report is suppressed and host 2 sends its membership report for group 224.1.1.1 first. Host 1 receives the report from host 2. Because only one membership report per group needs to be sent to the router, other hosts suppress their reports to reduce network traffic. Each host waits for a random time interval to avoid sending reports at the same time. You can configure the query maximum response time parameter to control the interval in which hosts randomize their responses.


Note

IGMPv1 and IGMPv2 membership report suppression occurs only on hosts that are connected to the same port.

In this Figure, router A sends the IGMPv3 group-and-source-specific query to the LAN. Hosts 2 and 3 respond to the query with membership reports that indicate that they want to receive data from the advertised group and source. This IGMPv3 feature supports SSM. For information about configuring SSM translation to support SSM for IGMPv1 and IGMPv2 hosts, seeConfiguring an IGMP SSM Translation.

Figure 2. IGMPv3 Group-and-Source-Specific Query


Note

IGMPv3 hosts do not perform IGMP membership report suppression.

Messages sent by the designated querier have a time-to-live (TTL) value of 1, which means that the messages are not forwarded by the directly connected routers on the subnet. You can configure the frequency and number of query messages sent specifically for IGMP startup, and you can configure a short query interval at startup so that the group state is established as quickly as possible. Although usually unnecessary, you can tune the query interval used after startup to a value that balances the responsiveness to host group membership messages and the traffic created on the network.


Caution

Changing the query interval can severely impact multicast forwarding.

When a multicast host leaves a group, a host that runs IGMPv2 or later sends an IGMP leave message. To check if this host is the last host to leave the group, the software sends an IGMP query message and starts a timer that you can configure called the last member query response interval. If no reports are received before the timer expires, the software removes the group state. The router continues to send multicast traffic for a group until its state is removed.

You can configure a robustness value to compensate for packet loss on a congested network. The robustness value is used by the IGMP software to determine the number of times to send messages.

Link local addresses in the range 224.0.0.0/24 are reserved by the Internet Assigned Numbers Authority (IANA). Network protocols on a local network segment use these addresses; routers do not forward these addresses because they have a TTL of 1. By default, the IGMP process sends membership reports only for nonlink local addresses, but you can configure the software to send reports for link local addresses.

For more information about configuring the IGMP parameters, seeConfiguring IGMP Interface Parameters.

Virtualization Support

A virtual device context (VDC) is a logical representation of a set of system resources. Within each VDC, you can define multiple virtual routing and forwarding (VRF) instances. One IGMP process can run per VDC. The IGMP process supports all VRFs in that VDC and performs the function of IGMP snooping within that VDC. For information about IGMP snooping, see Configuring IGMP Snooping.

You can use the show commands with a VRF argument to provide a context for the information displayed. The default VRF is used if no VRF argument is supplied.

For information about configuring VDCs, see Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide.

For information about configuring VRFs, see Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide.

Licensing Requirements for IGMP

Product

License Requirement

Cisco NX-OS

IGMP requires no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see theCisco NX-OS Licensing Guide.

Prerequisites for IGMP

IGMP has the following prerequisites:

  • You are logged onto the device.
  • You are in the correct virtual device context (VDC). A VDC is a logical representation of a set of system resources. You can use the switchto vdc command with a VDC number.
  • For global configuration commands, you are in the correct virtual routing and forwarding (VRF) mode. The default configuration mode shown in the examples in this chapter applies to the default VRF.

Default Settings for IGMP

This Table lists the default settings for IGMP parameters.

Table 1 Default IGMP Parameters

Parameters

Default

IGMP version

2

Startup query interval

30 seconds

Startup query count

2

Robustness value

2

Querier timeout

255 seconds

Query timeout

255 seconds

Query max response time

10 seconds

Query interval

125 seconds

Last member query response interval

1 second

Last member query count

2

Group membership timeout

260 seconds

Report link local multicast groups

Disabled

Enforce router alert

Disabled

Immediate leave

Disabled

Configuring IGMP Parameters

You can configure the IGMP global and interface parameters to affect the operation of the IGMP process.


Note

If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Configuring IGMP Interface Parameters

You can configure the optional IGMP interface parameters described in the Table below.

Table 2 IGMP Interface Parameters

Parameter

Description

IGMP version

IGMP version that is enabled on the interface. The IGMP version can be 2 or 3. The default is 2.

Static multicast groups

Multicast groups that are statically bound to the interface. You can configure the groups to join the interface with the (*, G) state or specify a source IP to join with the (S, G) state. You can specify a route-map policy name that lists the group prefixes, group ranges, and source prefixes to use with thematch ip multicast command.

Note   

Although you can configure the (S, G) state, the source tree is built only if you enable IGMPv3. For information about SSM translation, see Configuring an IGMP SSM Translation .

You can configure a multicast group on all the multicast-capable routers on the network so that pinging the group causes all the routers to respond.

Static multicast groups on OIF

Multicast groups that are statically bound to the output interface. You can configure the groups to join the output interface with the (*, G) state or specify a source IP to join with the (S, G) state. You can specify a route-map policy name that lists the group prefixes, group ranges, and source prefixes to use with the match ip multicast command.

Note   

Although you can configure the (S, G) state, the source tree is built only if you enable IGMPv3. For information about SSM translation, see the Configuring an IGMP SSM Translation .

Startup query interval

Startup query interval. By default, this interval is shorter than the query interval so that the software can establish the group state as quickly as possible. Values range from 1 to 18,000 seconds. The default is 31 seconds.

Startup query count

Number of queries sent at startup that are separated by the startup query interval. Values range from 1 to 10. The default is 2.

Robustness value

Robustness variable that you can tune to reflect expected packet loss on a congested network. You can increase the robustness variable to increase the number of times that packets are resent. Values range from 1 to 7. The default is 2.

Querier timeout

Number of seconds that the software waits after the previous querier has stopped querying and before it takes over as the querier. Values range from 1 to 65,535 seconds. The default is 255 seconds.

Query max response time

Maximum response time advertised in IGMP queries. You can tune the burstiness of IGMP messages on the network by setting a larger value so that host responses are spread out over a longer time. This value must be less than the query interval. Values range from 1 to 25 seconds. The default is 10 seconds.

Query interval

Frequency at which the software sends IGMP host query messages. You can tune the number of IGMP messages on the network by setting a larger value so that the software sends IGMP queries less often. Values range from 1 to 18,000 seconds. The default is 125 seconds.

Last member query response interval

Interval in which the software sends a response to an IGMP query after receiving a host leave message from the last known active host on the subnet. If no reports are received in the interval, the group state is deleted. You can use this value to tune how quickly the software stops transmitting on the subnet. The software can detect the loss of the last member of a group or source more quickly when the values are smaller. Values range from 1 to 25 seconds. The default is 1 second.

Last member query count

Number of times that the software sends an IGMP query, separated by the last member query response interval, in response to a host leave message from the last known active host on the subnet. Values range from 1 to 5. The default is 2.

Setting this value to 1 means that a missed packet in either direction causes the software to remove the multicast state from the queried group or channel. The software may wait until the next query interval before the group is added again.

Group membership timeout

Group membership interval that must pass before the router decides that no members of a group or source exist on the network. Values range from 3 to 65,535 seconds. The default is 260 seconds.

Report link local multicast groups

Option that enables sending reports for groups in 224.0.0.0/24. Link local addresses are used only by protocols on the local network. Reports are always sent for nonlink local groups. The default is disabled.

Report policy

Access policy for IGMP reports that is based on a route-map policy.

1

Access groups

Option that configures a route-map policy to control the multicast groups that hosts on the subnet serviced by an interface can join.

Note   

Only the match ip multicast group command is supported in this route map policy. The match ip address command for matching an ACL is not supported.

Immediate leave

Option that minimizes the leave latency of IGMPv2 group memberships on a given IGMP interface because the device does not send group-specific queries. When immediate leave is enabled, the device will remove the group entry from the multicast routing table immediately upon receiving a leave message for the group. The default is disabled.

Note   

Use this command only when there is one receiver behind the interface for a given group.
1

To configure route-map policies, see the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide.

For information about configuring multicast route maps, see Configuring Route Maps to Control RP Information Distributior.

Procedure
     Command or ActionPurpose
    Step 1config t


    Example:
    switch# config t
switch(config)#
     

    Enters configuration mode.

     
    Step 2interface interface


    Example:
    switch(config)# interface ethernet 2/1
switch(config-if)#
     

    Enters interface mode on the interface type and number, such as ethernet slot/port.

     
    Step 3
    Option Description
    ip igmp version value

    Example

    switch(config-if)# ip igmp version 3

    Sets the IGMP version to the value specified. Values can be 2 or 3. The default is 2.

    Theno form of the command sets the version to 2.
    ip igmp join-group {group [source source] | route-map policy-name}

    Example

    switch(config-if)# ip igmp join-group 230.0.0.0

    Statically binds a multicast group to the outgoing interface, which is handled by the device hardware. If you specify only the group address, the (*, G) state is created. If you specify the source address, the (S, G) state is created. You can specify a route-map policy name that lists the group prefixes, group ranges, and source prefixes to use with the match ip multicast command.

    Note   

    A source tree is built for the (S, G) state only if you enable IGMPv3.

    Caution   

    The device CPU must be able to handle the traffic generated by using this command. Because of CPU load constraints, using this command, especially in any form of scale, is not recommended. Consider using the ip igmp static-oif command instead.
    ip igmp static-oif {group [source source] | route-map policy-name}

    Example

    switch(config-if)# ip igmp static-oif 230.0.0.0

    Statically binds a multicast group to the outgoing interface, which is handled by the device hardware. If you specify only the group address, the (*, G) state is created. If you specify the source address, the (S, G) state is created. You can specify a route-map policy name that lists the group prefixes, group ranges, and source prefixes to use with the match ip multicast command.

    Note   

    A source tree is built for the (S, G) state only if you enable IGMPv3.
    ip igmp startup-query-interval seconds

    Example

    switch(config-if)# ip igmp startup-query-interval 25

    Sets the query interval used when the software starts up. Values can range from 1 to 18,000 seconds. The default is 31 seconds.
    ip igmp startup-query-count count

    Example

    switch(config-if)# ip igmp startup-query-count 3

    Sets the query count used when the software starts up. Values can range from 1 to 10. The default is 2.
    ip igmp robustness-variable value

    Example

    switch(config-if)# ip igmp robustness-variable 3

    Sets the robustness variable. You can use a larger value for a lossy network. Values can range from 1 to 7. The default is 2.
    ip igmp querier-timeout seconds

    Example

    switch(config-if)# ip igmp querier-timeout 300

    Sets the querier timeout that the software uses when deciding to take over as the querier. Values can range from 1 to 65,535 seconds. The default is 255 seconds.
    ip igmp query-timeout seconds

    Example

    switch(config-if)# ip igmp query-timeout 300

    Sets the query timeout that the software uses when deciding to take over as the querier. Values can range from 1 to 65,535 seconds. The default is 255 seconds.

    Note   

    This command has the same functionality as the ip igmp querier-timeout command.
    ip igmp query-max-response-time seconds

    Example

    switch(config-if)# ip igmp query-max-response-time 15

    Sets the response time advertised in IGMP queries. Values can range from 1 to 25 seconds. The default is 10 seconds.
    ip igmp query-interval interval

    Example

    switch(config-if)# ip igmp query-interval 100

    Sets the frequency at which the software sends IGMP host query messages. Values can range from 1 to 18,000 seconds. The default is 125 seconds.
    ip igmp last-member-query-response-time seconds

    Example

    switch(config-if)# ip igmp last-member-query-response-time 3

    Sets the query interval waited after sending membership reports before the software deletes the group state. Values can range from 1 to 25 seconds. The default is 1 second.
    ip igmp last-member-query-count count

    Example

    switch(config-if)# ip igmp last-member-query-count 3

    Sets the number of times that the software sends an IGMP query in response to a host leave message. Values can range from 1 to 5. The default is 2.
    ip igmp group-timeout seconds

    Example

    switch(config-if)# ip igmp group-timeout 300

    Sets the group membership timeout for IGMPv2. Values can range from 3 to 65,535 seconds. The default is 260 seconds.
    ip igmp report-link-local-groups

    Example

    switch(config-if)# ip igmp report-link-local-groups

    Enables sending reports for groups in 224.0.0.0/24. Reports are always sent for nonlink local groups. By default, reports are not sent for link local groups.
    ip igmp report-policy policy

    Example

    switch(config-if)# ip igmp report-policy my_report_policy

    Configures an access policy for IGMP reports that is based on a route-map policy.
    ip igmp access-group policy

    Example

    switch(config-if)# ip igmp access-group my_access_policy

    Configures a route-map policy to control the multicast groups that hosts on the subnet serviced by an interface can join.

    Note   

    Only the match ip multicast group command is supported in this route map policy. The match ip address command for matching an ACL is not supported.
    ip igmp immediate-leave

    Example

    switch(config-if)# ip igmp immediate-leave

    Enables the device to remove the group entry from the multicast routing table immediately upon receiving a leave message for the group. Use this command to minimize the leave latency of IGMPv2 group memberships on a given IGMP interface because the device does not send group-specific queries. The default is disabled.

    Note   

    Use this command only when there is one receiver behind the interface for a given group.
     

    These commands are used to configure the IGMP interface parameters.

     
    Step 4show ip igmp interface [interface] [vrf vrf-name | all] [brief]


    Example:
    switch(config)# show ip igmp interface
     

    (Optional) Displays IGMP information about the interface.

     
    Step 5copy running-config startup-config


    Example:
    switch(config)# copy running-config startup-config
     

    (Optional) Saves configuration changes.

     

    Configuring an IGMP SSM Translation

    You can configure an SSM translation to provide SSM support when the router receives IGMPv1 or IGMPv2 membership reports. Only IGMPv3 provides the capability to specify group and source addresses in membership reports. By default, the group prefix range is 232.0.0.0/8. To modify the PIM SSM range, see Configuring SSM.

    This Table lists the example SSM translations.

    Table 3 Example SSM Translations

    Group Prefix

    Source Address

    232.0.0.0/8

    10.1.1.1

    232.0.0.0/8

    10.2.2.2

    232.1.0.0/16

    10.3.3.3

    232.1.1.0/24

    10.4.4.4

    This Table shows the resulting MRIB routes that the IGMP process creates when it applies an SSM translation to the IGMP membership report. If more than one translation applies, the router creates the (S, G) state for each translation.

    Table 4 Example Result of Applying SSM Translations

    IGMPv2 Membership Report

    Resulting MRIB Route

    232.1.1.1

    (10.4.4.4, 232.1.1.1)

    232.2.2.2

    (10.1.1.1, 232.2.2.2)
(10.2.2.2, 232.2.2.2)

    Note

    This feature is similar to SSM mapping found in some Cisco IOS software.

    Procedure
       Command or ActionPurpose
      Step 1config t Example:


      Example:
      switch# config t
switch(config)#
       

      Enters configuration mode.

       
      Step 2ip igmp ssm-translategroup-prefix source-addr


      Example:
      switch(config)# ip igmp ssm-translate 232.0.0.0/8 10.1.1.1
       

      Configures the translation of IGMPv1 or IGMPv2 membership reports by the IGMP process to create the (S,G) state as if the router had received an IGMPv3 membership report.

       
      Step 3show running-configuration igmp


      Example:
      switch(config)# show running-configuration igmp
       

      (Optional) Shows the running-configuration information, including ssm-translate command lines.

       
      Step 4copy running-config startup-config


      Example:
      switch(config)# copy running-config startup-config
       

      (Optional) Saves configuration changes.

       

      Configuring the Enforce Router Alert Option Check

      You can configure the enforce router alert option check for IGMPv2 and IGMPv3 packets.

      Procedure
         Command or ActionPurpose
        Step 1config t


        Example:
        switch# config t
switch(config)#
         

        Enters configuration mode.

         
        Step 2ip igmp enforce-router-alert


        Example:
        switch(config)# ip igmp enforce-router-alert
         

        Enables the enforce router alert option check for IGMPv2 and IGMPv3 packets. By default, the enforce router alert option check is enabled.

         
        Step 3no ip igmp enforce-router-alert


        Example:
        switch(config)# no ip igmp enforce-router-alert
         

        Disables the enforce router alert option check for IGMPv2 and IGMPv3 packets. By default, the enforce router alert option check is enabled.

         
        Step 4show running-configuration igmp


        Example:
        switch(config)# show running-configuration igmp
         

        (Optional) Shows the running-configuration information, including the enforce-router-alert command line.

         
        Step 5copy running-config startup-config


        Example:
        switch(config)# copy running-config startup-config
         

        (Optional) Saves configuration changes.

         

        Restarting the IGMP Process

        You can restart the IGMP process and optionally flush all routes.

        Procedure
           Command or ActionPurpose
          Step 1restart igmp


          Example:
          switch# restart igmp
           

          Restarts the IGMP process.

           
          Step 2config t


          Example:
          switch# config t
switch(config)#
           

          Enters configuration mode.

           
          Step 3ip igmp flush-routes


          Example:
          switch(config)# ip igmp flush-routes
           

          Removes routes when the IGMP process is restarted. By default, routes are not flushed.

           
          Step 4show running-configuration igmp


          Example:
          switch(config)# show running-configuration igmp
           

          (Optional) Shows the running-configuration information, including flush-routescommand lines.

           
          Step 5copy running-config startup-config


          Example:
          switch(config)# copy running-config startup-config
           

          (Optional) Saves configuration changes.

           

          Verifying the IGMP Configuration

          To display the IGMP configuration information, perform one of the following tasks:

             

          show ip igmp interface [interface] [vrf vrf-name | all] [brief]

          Displays IGMP information about all interfaces or a selected interface, the default VRF, a selected VRF, or all VRFs. If IGMP is in vPC mode. Use this command to display vPC statistics.

          show ip igmp groups [{source [group]}] | {group [source]}] [interface] [summary] [vrf vrf-name | all]

          Displays the IGMP attached group membership for a group or interface, the default VRF, a selected VRF, or all VRFs.

          show ip igmp route [{source [group]}] | {group [source]}] [interface] [summary] [vrf vrf-name | all]

          Displays the IGMP attached group membership for a group or interface, the default VRF, a selected VRF, or all VRFs.

          show ip igmp local-groups

          Displays the IGMP local group membership.

          show running-configuration igmp

          Displays the IGMP running-configuration information.

          show startup-configuration igmp

          Displays the IGMP startup-configuration information.

          For detailed information about the fields in the output from these commands, see the Cisco Nexus 7000 Series NX-OS Multicast Routing Command Reference.

          Configuration Examples for IGMP

          The following example shows how to configure the IGMP parameters:

          
config t
  ip igmp ssm-translate 232.0.0.0/8 10.1.1.1
  interface ethernet 2/1
    ip igmp version 3
    ip igmp join-group 230.0.0.0
    ip igmp startup-query-interval 25
    ip igmp startup-query-count 3
    ip igmp robustness-variable 3
    ip igmp querier-timeout 300
    ip igmp query-timeout 300
    ip igmp query-max-response-time 15
    ip igmp query-interval 100
    ip igmp last-member-query-response-time 3
    ip igmp last-member-query-count 3
    ip igmp group-timeout 300
    ip igmp report-link-local-groups
    ip igmp report-policy my_report_policy
    ip igmp access-group my_access_policy

          Feature History for IGMP

          This Table lists the release history for this feature.

          Table 5 Feature History for IGMP

          Feature Name

          Releases

          Feature Information

          ip igmp groups and ip igmp route commands.

          6.1(1)

          Commands updated with summary parameter.

          • ip igmp groups
          • ip igmp route

          vPC

          4.1(3)

          Displays vPC statistics with the show ip igmp interface command.

          The following section provides information about this feature:

          • Verifying the IGMP Configuration

          Immediate Leave

          4.1(3)

          Minimizes the leave latency of IGMPv2 or MLDv1 group memberships on a given IGMP or MLD interface because the device does not send group-specific queries.

          For more information, see Configuring IGMP Interface Parameters