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Example: Configuring PIM RPF Selection

Requirements

Before you begin:

• Configure the router interfaces. See the Junos OS Network Interfaces Library for Routing Devices.
• Configure an interior gateway protocol or static routing. See the Junos OS Routing Protocols Library for Routing Devices.
• Make sure that the RPF next-hop neighbor you want to specify is operating.

Overview

Multicast PIM RPF neighbor selection allows you to specify the RPF neighbor (next hop) and source address for a single group or multiple groups using a prefix list. RPF neighbor selection can only be configured for VPN routing and forwarding (VRF) instances.

If you have multiple service VRFs through which a receiver VRF can learn the same source or rendezvous point (RP) address, PIM RPF checks typically choose the best path determined by the unicast protocol for all multicast flows. However, if RPF neighbor selection is configured, RPF checks are based on your configuration instead of the unicast routing protocols.

You can use this static RPF selection as a building block for particular applications. For example, an extranet. Suppose you want to split the multicast flows among parallel PIM links or assign one multicast flow to a specific PIM link. With static RPF selection configured, the router sends join and prune messages based on the configuration.

You can use wildcards to designate the source address. Whether or not you use wildcards affects how the PIM joins work:

• If you configure only a source prefix for a group, all (*,G) joins are sent to the next-hop neighbor selected by the unicast protocol, while (S,G) joins are sent to the next-hop neighbor specified for the source.
• If you configure only a wildcard source for a group, all (*,G) and (S,G) joins are sent to the upstream interface pointing to the wildcard source next-hop neighbor.
• If you configure both a source prefix and a wildcard source for a group, all (S,G) joins are sent to the next-hop neighbor defined for the source prefix, while (*,G) joins are sent to the next-hop neighbor specified for the wildcard source.

Figure 1 shows the topology used in this example.

Figure 1: PIM RPF Selection

In this example, the RPF selection is configured on the receiver provider edge router (PE2).

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. On PE2, configure RFP selection in a routing instance.
   [edit routing-instance vpn-a protocols pim]user@host# set rpf-selection group 225.5.0.0/16 wildcard-source next-hop 10.12.5.2user@host# set rpf-selection prefix-list group12 wildcard-source next-hop 10.12.31.2 user@host# set rpf-selection prefix-list group34 source 22.1.12.0/24 next-hop 10.12.32.2 user@host# exit
2. On PE2, configure the policy.
   [edit policy-options]set prefix-list group12 225.1.1.0/24 set prefix-list group12 225.2.0.0/16 set prefix-list group34 225.3.3.3/32 set prefix-list group34 225.4.4.0/24
3. If you are done configuring the device, commit the configuration.
   user@host# commit

Results

From configuration mode, confirm your configuration by entering the show policy-options and show routing-instances commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

To verify the configuration, run the following commands, checking the upstream interface and the upstream neighbor:

• show pim join extensive
• show multicast route