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Example: Enabling Join Suppression

Requirements

Before you begin:

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

Overview

PIM join suppression enables a router on a multiaccess network to defer sending join messages to an upstream router when it sees identical join messages on the same network. Eventually, only one router sends these join messages, and the other routers suppress identical messages. Limiting the number of join messages improves scalability and efficiency by reducing the number of messages sent to the same router.

• override-interval—Sets the maximum time in milliseconds to delay sending override join messages. When a router sees a prune message for a join it is currently suppressing, it waits before it sends an override join message. Waiting helps avoid multiple downstream routers sending override join messages at the same time. The override interval is a random timer with a value of 0 through the maximum override value.
• propagation-delay—Sets a value in milliseconds for a prune pending timer, which specifies how long to wait before executing a prune on an upstream router. During this period, the router waits for any prune override join messages that might be currently suppressed. The period for the prune pending timer is the sum of the override-interval value and the value specified for propagation-delay.
• reset-tracking-bit—Enables PIM join suppression on each multiaccess downstream interface. This statement resets a tracking bit field (T-bit) on the LAN prune delay hello option from the default of 1 (join suppression disabled) to 0 (join suppression enabled).

  When multiple identical join messages are received, a random join suppression timer is activated, with a range of 66 through 84 milliseconds. The timer is reset each time join suppression is triggered.

Figure 1 shows the topology used in this example.

Figure 1: Join Suppression

• Host 0 is the multicast source.
• Host 1, Host 2, Host 3, and Host 4 are receivers.
• Router R0 is the first-hop router and the RP.
• Router R1 is an upstream router.
• Routers R2, R3, R4, and R5 are downstream routers in the multicast LAN.

This example shows the configuration of the downstream devices: Routers R2, R3, R4, and R5.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Step-by-Step Procedure

1. Configure PIM sparse mode on the interfaces.

   [edit]user@host# edit protocols pim[edit protocols pim]user@host# set rp static address 10.255.112.160[edit protocols pim]user@host# set interface all mode sparse version 2[edit protocols pim]user@host# set interface all version 2[edit protocols pim]user@host# set interface fxp0.0 disable

2. Enable the join suppression timer.

   [edit protocols pim]user@host# set reset-tracking-bit

3. Configure the prune override interval value.

   [edit protocols pim]user@host# set override-interval 4000

4. Configure the propagation delay of the link.

   [edit protocols pim]user@host# set propagation-delay 500

5. (Optional) Configure PIM tracing operations.

   [edit protocols pim]user@host# set traceoptions file pim.log size 5m world-readable[edit protocols pim]user@host# set traceoptions flag join detail[edit protocols pim]user@host# set traceoptions flag normal detail[edit protocols pim]user@host# set traceoptions flag register detail

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

   [edit protocols pim]user@host# commit

Results

From configuration mode, confirm your configuration by entering the show protocols command. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

• show pim join extensive
• show multicast route extensive