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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
Before you begin, configure the router interfaces.
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 1). 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 1 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 and then builds it out hop by hop until it reaches the source. In Figure 2, 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 3).
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.
Topology
This example works with the simple RPF topology shown in Figure 4.
Configuration
Procedure
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,
copy and paste the commands into the CLI at the [edit] hierarchy
level, and then enter commit from configuration mode.
set protocols ospf area 0.0.0.0 interface fxp0.0 disable set protocols ospf area 0.0.0.0 interface all set protocols pim rp local address 10.255.72.46 set protocols pim rp local group-ranges 239.0.0.0/24 set protocols pim interface fe-1/0/0.0 mode sparse set protocols pim interface lo0.0 mode sparse set routing-options multicast ssm-groups 232.0.0.0/8 set routing-options multicast ssm-groups 239.0.0.0/8 set routing-options multicast asm-override-ssm
Step-by-Step Procedure
The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.
To configure an RPF policy:
Configure OSPF.
[edit protocols ospf] user@host# set area 0.0.0.0 interface fxp0.0 disable user@host# set area 0.0.0.0 interface all
Configure PIM sparse mode.
[edit protocols pim] user@host# set rp local address 10.255.72.46 user@host# set rp local group-ranges 239.0.0.0/24 user@host# set interface fe-1/0/0.0 mode sparse user@host# set interface lo0.0 mode sparse
Configure additional SSM groups.
[edit routing-options] user@host# set ssm-groups [ 232.0.0.0/8 239.0.0.0/8 ]
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
If you are done configuring the device, commit the configuration.
user@host# commit
Results
Confirm your configuration by entering the show
protocols and show routing-options commands.
user@host# show protocols
ospf {
area 0.0.0.0 {
interface fxp0.0 {
disable;
}
interface all;
}
}
pim {
rp {
local {
address 10.255.72.46;
group-ranges {
239.0.0.0/24;
}
}
}
interface fe-1/0/0.0 {
mode sparse;
}
interface lo0.0 {
mode sparse;
}
}
user@host# show routing-options
multicast {
ssm-groups [ 232.0.0.0/8 239.0.0.0/8 ];
asm-override-ssm;
}
Verification
To verify the configuration, run the following commands:
show igmp group
show igmp statistics
show pim join