Example: Configuring Source-Specific Multicast Groups with Any-Source Override

This example shows how to extend source-specific multicast (SSM) group operations beyond the default IP address range of 232.0.0.0 through 232.255.255.255. This example also shows how to accept any-source multicast (ASM) join messages (*,G) for group addresses that are within the default or configured range of SSM groups. This allows you to support a mix of any-source and source-specific multicast groups simultaneously.

• Requirements
• Overview
• Configuration
• Verification

Requirements

Before you begin, configure the router interfaces. See the Network Interfaces Configuration Guide.

Overview

To deploy SSM, configure PIM sparse mode on all routing device interfaces and issue the necessary SSM commands, including specifying IGMPv3 or MLDv2 on the receiver's LAN. If PIM sparse mode is not explicitly configured on both the source and group members interfaces, multicast packets are not forwarded. Source lists, supported in IGMPv3 and MLDv2, are used in PIM SSM. Only sources that are specified send traffic to the SSM group.

In a PIM SSM-configured network, a host subscribes to an SSM channel (by means of IGMPv3 or MLDv2) to join group G and source S (see Figure 38). The directly connected PIM sparse-mode router, the receiver's designated router (DR), sends an (S,G) join message to its reverse-path forwarding (RPF) neighbor for the source. Notice in Figure 38 that the RP is not contacted in this process by the receiver, as would be the case in normal PIM sparse-mode operations.

The (S,G) join message initiates the source tree, then builds it out hop by hop until it reaches the source. In Figure 39, the source tree is built across the network to Router 3, the last-hop router connected to the source.

Using the source tree, multicast traffic is delivered to the subscribing host (see Figure 40).

SSM can operate in include mode or in exclude mode. In exclude mode the receiver specifies a list of sources that it does not want to receive the multicast group traffic from. The routing device forwards traffic to the receiver from any source except the sources specified in the exclusion list. The receiver accepts traffic from any sources except the sources specified in the exclusion list.

This example works with the simple topology shown in Figure 41.

Configuration

CLI Quick Configuration

To quickly configure an RPF policy, copy the following commands and paste the commands 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 RPF policy:

1. Configure OSPF.

   [edit]user@host# edit protocols ospf[edit protocols ospf]user@host# set area 0.0.0.0 interface fxp0.0 disable[edit protocols ospf]user@host# set area 0.0.0.0 interface all

2. Configure PIM sparse mode.

   [edit]user@host# edit protocols pim[edit protocols pim]user@host# set rp local address 10.255.72.46[edit protocols pim]user@host# set rp local group-ranges 239.0.0.0/24[edit protocols pim]user@host# set interface fe-1/0/0.0 mode sparse[edit protocols pim]user@host# set interface lo0.0 mode sparse

3. Configure additional SSM groups.

   [edit]user@host# edit routing-options[edit routing-options]user@host# set ssm-groups [ 232.0.0.0/8 239.0.0.0/8 ]

4. Configure the RP to accept ASM join messages for groups within the SSM address range.

   [edit routing-options]user@host# set multicast asm-override-ssm

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

   [edit routing-instances]user@host# commit

Results

Confirm your configuration by entering the show protocols and show routing-options commands.

Verification

To verify the configuration, run the following commands:

• show igmp group
• show igmp statistics
• show pim join

Related Topics

• Source-Specific Multicast Groups Overview