Cisco IGMP Explicit Tracking: User and Service Manual PDF

Restrictions for IGMP Explicit Tracking

IGMP Explicit Tracking This module describes the explicit tracking of hosts, groups, and channels for the Internet Group Management Protocol (IGMP). Restrictions for IGMP Explicit Tracking, on page 1 Information About IGMP Explicit Tracking, on page 2 How to Configure IGMP Explicit Tracking, on page 3 Configuration Examples for IGMP Explicit Tracking, on page 4 Verifying IGMP Explicit Tracking, on page 5 Additional References for IGMP Explicit Tracking, on page 7 Feature History for IGMP Explicit Tracking, on page 8 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). IGMP Explicit Tracking 1

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Improved Diagnostic Capabilities

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. IGMP Explicit Tracking Information About IGMP Explicit Tracking IGMP Explicit Tracking 2

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Enabling Explicit Tracking on Layer 3 Interfaces

How to Configure IGMP Explicit Tracking Enabling Explicit Tracking Globally You can enable explicit-tracking globally and on Layer 3 interfaces. Procedure Enabling Explicit Tracking on Layer 3 Interfaces You can enable explicit-tracking globally and on Layer 3 interfaces. Procedure IGMP Explicit Tracking How to Configure IGMP Explicit Tracking 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. 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. IGMP Explicit Tracking 3

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Example: Enabling Explicit Tracking

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 IGMP Explicit Tracking Configuration Examples for IGMP Explicit Tracking Command or Action Purpose 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. IGMP Explicit Tracking 4

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