Published On: August 10ᵗʰ, 2021 02:10

IP Multicast Routing Configuration Guide, Cisco IOS XE Amsterdam 17.3.x (Catalyst 9500 Switches)

Contents

This module describes the explicit tracking of hosts, groups, and channels for the Internet Group Management Protocol (IGMP).

Restrictions for IGMP Explicit Tracking

The following restrictions apply to this feature.

  • If one or more hosts that supports only IGMP Version 1 or Version 2 are present on a network, the leave latencies for the multicast groups to which these hosts are joined will revert to the leave latencies of the IGMP version of the hosts—approximately 3 seconds for IGMP Version 2 and up to 180 seconds for IGMP Version 1. This condition affects only multicast groups to which these legacy hosts are actually joined at any given point in time. In addition, the membership reports for these multicast groups sent by IGMPv3 hosts may revert to IGMP Version 1 or Version 2 membership reports, thus disabling explicit tracking of those host memberships.

  • Explicit tracking of IGMP Version 3 lite (IGMP v3lite) or URL Rendezvous Directory (URD) channel membership reports is not supported. Therefore, the leave latency for multicast groups sending traffic to hosts using IGMPv3 lite or URD will be determined by the leave latency of the version of IGMP configured on the hosts (for IGMPv3, the leave latency is typically 3 seconds when explicit tracking is not configured).

Information About IGMP Explicit Tracking

IGMP Explicit Tracking

The Internet Group Management Protocol (IGMP) is used by IP hosts to report their multicast group memberships to neighboring multicast devices. The IGMP Explicit Tracking feature enables a multicast device to explicitly track the membership of all multicast hosts in a particular multiaccess network. IGMP explicit tracking can be enabled globally and on Layer3 interfaces.

The explicit tracking of hosts, groups, and channels enables the device to keep track of each individual host that is joined to a particular group or channel. The main benefits of this feature are that it provides minimal leave latencies, faster channel changing, and improved diagnostics capabilities for IGMP.

Minimal Leave Latencies

The main benefit of the explicit tracking of hosts, groups, and channels in IGMP is to allow minimal leave latencies when a host leaves a multicast group or channel. The length of time between a host wanting to leave and a device stopping traffic forwarding is called the IGMP leave latency. A device configured with IGMP Version 3 (IGMPv3) and explicit tracking can immediately stop forwarding traffic if the last host to request to receive traffic from the device indicates that it no longer wants to receive traffic. The leave latency is thus bound only by the packet transmission latencies in the multiaccess network and the processing time in the device.

In IGMP Version 2, when a device receives an IGMP leave message from a host, it must first send an IGMP group-specific query to learn if other hosts on the same multiaccess network are still requesting to receive traffic. If after a specific time (the default value is approximately 3 seconds) no host replies to the query, the device will then stop forwarding the traffic. This query process is required because, in IGMP Version 1 and 2, IGMP membership reports are suppressed if the same report is already sent by another host in the network. Therefore, it is impossible for the device to reliably know how many hosts on a multiaccess network are requesting to receive traffic.

Faster Channel Changing

In networks where bandwidth is constrained between multicast devices and hosts (like in xDSL deployments), the bandwidth between devices and hosts is typically large enough to only sustain, in general, N multicast streams to be received in parallel. In these deployments, each host will typically join to only one multicast stream and the overall number of allowed hosts will be limited to N. The effective leave latency in these environments defines the channel change time of the receiver application—a single host cannot receive the new multicast stream before forwarding of the old stream has stopped. If an application tries to change the channel faster than the leave latency, the application will overload the bandwidth of the access network, resulting in a temporary degradation of traffic flow for all hosts. The explicit tracking of hosts, groups, and channels in IGMP allows for minimal leave latencies, and thus allows for fast channel changing capabilities.

Improved Diagnostic Capabilities

The explicit tracking of hosts, groups, and channels in IGMP allows network administrators to easily determine which multicast hosts are joined to other multicast groups or channels.

How to Configure IGMP Explicit Tracking

Enabling Explicit Tracking Globally

You can enable explicit-tracking globally and on Layer 3 interfaces.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip igmp snooping vlan vlan-id explicit-tracking
  4. exit

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

ip igmp snooping vlan vlan-id explicit-tracking

Example:

Device(config)# ip igmp snooping vlan 1 explicit-tracking

Enables IGMP explicit host tracking.

Step 4

exit

Example:

Device(config)# exit

Exits global configuration mode and returns to privileged EXEC mode.

Enabling Explicit Tracking on Layer 3 Interfaces

You can enable explicit-tracking globally and on Layer 3 interfaces.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. ip address ip-address mask
  5. ip pim sparse-mode
  6. ip igmp version 3
  7. ip igmp explicit-tracking
  8. exit

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:

Device(config)# interface vlan 77

Configures an interface and enters interface configuration mode.

Step 4

ip address ip-address mask

Example:

Device(config-if)# ip address 10.1.1.1 255.255.255.254

Sets a primary or secondary IP address for an interface.

Step 5

ip pim sparse-mode

Example:

Device(config-if)# ip pim sparse-mode

Enables Protocol Independent Multicast (PIM) sparse mode on an interface.

Step 6

ip igmp version 3

Example:

Device(config-if)# ip igmp version 3

Configure Internet Group Management Protocol (IGMP) Version 3 (IGMPv3) on the device.

Step 7

ip igmp explicit-tracking

Example:

Device(config-if)# ip igmp explicit-tracking

Enables IGMP explicit host tracking.

Step 8

exit

Example:

Device(config)# exit

Exits global configuration mode and returns to privileged EXEC mode.

Configuration Examples for IGMP Explicit Tracking

Example: Enabling Explicit Tracking

The following example shows a basic configuration to enable IGMP explicit tracking globally:


Device# configure terminal 
Device(config)# ip multicast routing
Device(config)# ip igmp snooping vlan 1 explicit-tracking
Device(config)# end


The following example shows a basic configuration to enable IGMP explicit tracking on Layer 3 interfaces:


Device# configure terminal 
Device(config)# interface vlan 77
Device(config-if)# ip address 10.1.1.1 255.255.255.254
Device(config-if)# ip pim sparse-mode
Device(config-if)# ip igmp version 3
Device(config-if)# ip igmp explicit-tracking
Device(config-if)# end


Verifying IGMP Explicit Tracking

SUMMARY STEPS

  1. enable
  2. show ip igmp snooping vlan vlan-ID
  3. show ip igmp groups interface-type interface-number
  4. show ip igmp membership tracked
  5. show ip igmp snooping vlan vlan-ID

DETAILED STEPS

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

show ip igmp snooping vlan vlan-ID

Example:

Device# show ip igmp snooping vlan 77
Displays snooping information in a Catalyst VLAN.

Device# show  ip igmp  snooping vlan  77

Global IGMP Snooping configuration:
-------------------------------------------
IGMP snooping                : Enabled
IGMPv3 snooping              : Enabled
Report suppression           : Enabled
TCN solicit query            : Disabled
TCN flood query count        : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval   : 1000

Vlan 77:
--------
IGMP snooping                       : Enabled
IGMPv2 immediate leave              : Disabled
Explicit host tracking              : Enabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000
Device#


Step 3

show ip igmp groups interface-type interface-number

Example:

Device# show ip igmp groups GigabitEthernet 1/0/24
Displays the multicast groups that are directly connected to a device, and that are learned through IGMP.
show ip igmp groups GigabitEthernet 1/0/24

IGMP Connected Group Membership
Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted
203.0.113.245    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.244    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.247    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.246    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.241    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.240    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.243    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.242    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.253    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.252    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.221    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.254    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.249    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.248    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.251    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.250    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.228    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.229    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.230    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.231    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2      
203.0.113.224    GigabitEthernet1/0/24    00:00:35  stopped   10.34.34.2   


Step 4

show ip igmp membership tracked

Example:

Device# show ip igmp membership tracked

Displays the multicast groups with the explicit tracking feature enabled.


Device# show ip igmp  membership tracked

Flags: A  - aggregate, T - tracked
       L  - Local, S - static, V - virtual, R - Reported through v3 
       I - v3lite, U - Urd, M - SSM (S,G) channel 
       1,2,3 - The version of IGMP, the group is in
Channel/Group-Flags: 
       / - Filtering entry (Exclude mode (S,G), Include mode (G))
Reporter:
       <mac-or-ip-address> - last reporter if group is not explicitly tracked
       <n>/<m>      - <n> reporter in include mode, <m> reporter in exclude

 Channel/Group                  Reporter        Uptime   Exp.  Flags  Interface 
 *,203.0.113.10                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.10        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.11                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.11        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.14                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.14        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.15                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.15        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.12                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.12        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.13                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.13        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.19                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.19        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.18                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.18        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.17                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.17        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.16                  1/0             00:20:46 stop  3AT    Gi1/0/24
 192.168.0.2,203.0.113.16        10.34.34.2      00:20:46 02:59 T      Gi1/0/24
 *,203.0.113.40                  0/1             00:20:48 02:16 3LAT   Gi1/0/24
 *,209.165.201.1                 10.34.34.1      00:20:48 02:16 3LT    Gi1/0/24
Device#


Step 5

show ip igmp snooping vlan vlan-ID

Example:

Device# show ip igmp snooping vlan 77

Displays the IGMP snooping configuration on a VLAN.


Device# show  ip igmp  snooping vlan  77

Global IGMP Snooping configuration:
-------------------------------------------
IGMP snooping                : Enabled
IGMPv3 snooping              : Enabled
Report suppression           : Enabled
TCN solicit query            : Disabled
TCN flood query count        : 2
Robustness variable          : 2
Last member query count      : 2
Last member query interval   : 1000

Vlan 77:
--------
IGMP snooping                       : Enabled
IGMPv2 immediate leave              : Disabled
Explicit host tracking              : Enabled
Multicast router learning mode      : pim-dvmrp
CGMP interoperability mode          : IGMP_ONLY
Robustness variable                 : 2
Last member query count             : 2
Last member query interval          : 1000
Device#



Additional References for IGMP Explicit Tracking

Related Documents

Related Topic Document Title

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

See the IP Multicast Routing Commands section of the Command Reference (Catalyst 9500 Series Switches)

Feature History for IGMP Explicit Tracking

This table provides release and related information for the features explained in this module.

These features are available in all the releases subsequent to the one they were introduced in, unless noted otherwise.

Release

Feature

Feature Information

Cisco IOS XE Everest 16.6.1

IGMP Explicit Tracking

IGMP explicit tracking enables a multicast device to explicitly track the membership of all multicast hosts in a particular multiaccess network

Support for this feature was introduced only on the C9500-12Q, C9500-16X, C9500-24Q, C9500-40X models of the Cisco Catalyst 9500 Series Switches.

Cisco IOS XE Fuji 16.8.1a

IGMP Explicit Tracking

Support for this feature was introduced only on the C9500-32C, C9500-32QC, C9500-48Y4C, and C9500-24Y4C models of the Cisco Catalyst 9500 Series Switches.

Use the Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.