Using SSM

Problem

You want to directly join a multicast group without going through an RP.

Solution

Configure an SSM-only domain. First, enable PIM-SM on all interfaces on all routers in the domain:

	[edit protocols pim]
	aviva@RouterA# set interface all

Disable PIM on the routers out-of-band management interface. On J-series routers, this is the fe-0/0/0 interface:

	aviva@RouterA# set interface fe-0/0/0.0 disable

On M-series and T-series routers, it is the fxp0 interface:

	aviva@R1# set interface fxp0.0 disable

On the multicast receivers DR, turn on IGMPv3 on the interface that faces the receiving host:

	[edit protocols igmp]
	aviva@RouterA# set interface fe-0/0/1 version 3

Discussion

SSM modifies the standard PIM-SM model, sometimes also called any-source multicast (ASM), by allowing routers to directly join a multicast group without using the RP as an intermediary. SSM can be used with multicast applications that are running IGMPv3.

SSM is really just a subset of ASM (plain-old PIM-SM). With SSM, the receiver is able to specify the source (using IGMPv3), so the receivers DR sends an (S,G) message toward the source, and traffic flows down the SPT from the source to the receiver. SSM uses PIM-SM to get (S,G) state information. (PIM supports both (S,G) and (*,G) state.)So, just by turning on PIM-SM for an interface, it supports SSM and ASM. This configuration mechanism is very easy, so if you are new to multicast, you should consider choosing SSM as the multicast protocol.

The steps for configuring SSM are very straightforward. First, configure PIM-SM on all interfaces and on all routers in your domain. Just by turning on PIM-SM and nothing else on these routers, they support SSM for all router roles except the receivers DR. On the receivers DR, you need to enable IGMPv3 on the interface that connects to the receiving host. Heres what the configuration looks like:

	aviva@RouterA> show configuration protocols igmp
	interface fe-0/0/0.0 {
	 disable;
	}
	interface fe-0/0/1.0 {
	 version 3;
	}

The receiving host, typically a PC of some kind, must also be running IGMPv3.

Look at the IGMP interfaces to verify that the configuration has taken effect:

	aviva@RouterA> show igmp interface
	Interface: fe-0/0/1.0
	 Querier: 10.0.15.1
	 State: Up Timeout: 185 Version: 3 Groups: 0
	Interface: se-0/0/3.0
	 Querier: 10.0.16.1
	 State: Up Timeout: None Version: 2 Groups: 4
	Interface: se-0/0/2.0
	 Querier: 10.0.21.1
	 State: Up Timeout: None Version: 2 Groups: 4

	Configured Parameters:
	IGMP Query Interval: 125.0
	IGMP Query Response Interval: 10.0
	IGMP Last Member Query Interval: 1.0
	IGMP Robustness Count: 2

	Derived Parameters:
	IGMP Membership Timeout: 260.0
	IGMP Other Querier Present Timeout: 255.0

You see that fe-0/0/1, the interface facing the receiver, is running IGMPv3, and all other router interfaces are running IGMPv2, which is enabled automatically when you turn on PIM-SM.

For the network to be an SSM-only domain, make sure it contains no RP routers. If the router receives a bootstrap routing message, it will automatically build an RP mapping and the network will no longer be SSM-only.

If you are not sure that the domain has no RPs, or if you want to ensure that the domain continues using SSM if an RP is later configured, block any Bootstrap messages from entering or leaving the router:

	[edit policy-options]
	aviva@RouterA# set policy-statement block-bootstrap then reject

	[edit protocols pim]
	aviva@RouterA# set rp bootstrap-import block-bootstrap
	aviva@RouterA# set rp bootstrap-export block-bootstrap

See Also

RFC 3569, An Overview of Source-Specific Multicast (SSM)