Example: Configuring the PIM SPT Threshold Policy

This example shows how to apply a policy that suppresses the transition from the rendezvous-point tree (RPT) rooted at the RP to the shortest-path tree (SPT) rooted at the source.

• Requirements
• Overview
• Configuration
• Verification

Requirements

Before you begin:

• Configure the router interfaces. See the Network Interfaces Configuration Guide.
• Configure an interior gateway protocol or static routing. See the Routing Protocols Configuration Guide.
• Configure PIM Sparse Mode on the interfaces. See Enabling PIM Sparse Mode.

Overview

Multicast routing devices running PIM sparse mode can forward the same stream of multicast packets onto the same LAN through an RPT rooted at the RP or through an SPT rooted at the source. In some cases, the last-hop routing device needs to stay on the shared RPT to the RP and not transition to a direct SPT to the source. Receiving the multicast data traffic on SPT is optimal but introduces more state in the network, which might not be desirable in some multicast deployments. Ideally, low-bandwidth multicast streams can be forwarded on the SPT, and high-bandwidth streams can use the SPT. This examples shows how to configure such a policy.

This example includes the following settings:

• spt-threshold—Enables you to configure an SPT threshold policy on the last-hop routing device to control the transition to a direct SPT. When you include this statement in the main PIM instance, the PE router stays on the RPT for control traffic.
• infinity—An SPT cutover threshold of infinity applied to a source-group address pair means the last-hop routing device never transitions to a direct SPT. For all other source-group address pairs, the last-hop routing device transitions immediately to a direct SPT rooted at the source DR. This statement must reference a properly configured policy to set the SPT cutover threshold for a particular source-group pair to infinity. The use of values other than infinity for the SPT threshold is not supported. You can configure more than one policy.
• policy-statement—Configures the policy.

  The simplest type of SPT threshold policy uses a route filter and source address filter to specify the multicast group and source addresses and to set the SPT threshold for that pair of addresses to infinity. The policy is applied to the main PIM instance.

  This example sets the SPT transition value for the source-group pair 10.10.10.1 and 224.1.1.1 to infinity. When the policy is applied to the last-hop router, multicast traffic from this source-group pair will never transition to a direct SPT to the source. Traffic will continue to arrive through the RP. However, traffic for any other source-group address combination at this router will transition to a direct SPT to the source.

Several points are important when configuring the SPT threshold policy.

Configuration changes to the SPT threshold policy affect how the routing device handles the SPT transition:

• When the policy is configured for the first time, the routing device continues to transition to the direct SPT for the source-group address pair until the PIM-join state is cleared with the clear pim join command.

  Note: If you do not clear the PIM-join state when you apply the infinity policy configuration for the first time, you must apply it before the PE router is brought up.

• When the policy is deleted for a source-group address pair for the first time, the routing device does not transition to the direct SPT for that source-group address pair until the PIM-join state is cleared with the clear pim join command.
• When the policy is changed for a source-group address pair for the first time, the routing device does not use the new policy until the PIM-join state is cleared with the clear pim join command.

Configuration

CLI Quick Configuration

To quickly configure an SPT threshold policy, copy the following commands and paste them into the CLI.

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Modification of the Junos OS Configuration in Junos OS CLI, Release 10.3.

To configure an SPT threshold policy:

1. Apply the policy.

   [edit]user@host# edit protocols pim[edit protocols pim]user@host# set spt-threshold infinity spt-infinity-policy[edit protocols pim]user@host# exit
2. Configure the policy.
   [edit]user@host# edit policy-options policy-statement spt-infinity-policy[edit policy-options policy-statement spt-infinity-policy]user@host# set term one from route-filter 224.1.1.1/32 exact[edit policy-options policy-statement spt-infinity-policy]user@host# set term one from source-address-filter 10.10.10.1/32 exact[edit policy-options policy-statement spt-infinity-policy]user@host# set term one then accept[edit policy-options policy-statement spt-infinity-policy]user@host# set term two then reject[edit policy-options policy-statement spt-infinity-policy]user@host# exitpolicy-statement {

3. If you are done configuring the device, commit the configuration.

   [edit]user@host# commit

4. Cause the configuration to take effect.

   [edit]user@host# run clear pim join

Results

Confirm your configuration by entering the show policy-options command and the show protocols command from configuration mode. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

Verification

To verify the configuration, run the show pim join command.

Related Topics

• SPT Cutover Control