Multicast-Source Specific Multicast

IPv4 addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are currently designated 

as source-specific multicast (SSM) destination addresses and are reserved for use by

source-specific applications. PIM SSM uses the PIM sparse-mode functionality to create an

SPT between the receiver and the source, but builds the SPT without the help of an RP.

SSM builds shortest-path trees (SPTs) directly represented by (S,G) pairs. The “S” refers

to the source's unicast IP address, and the “G” refers to the specific multicast group address.

The SSM (S,G) pairs are called channels to differentiate them from any-source

multicast (ASM) groups. SSM uses no RP, instead it uses IGMP version 3 to signal what

channel (source) it wants to join for a group.

#ip pim ssm default

R3#
interface FastEthernet0/1
 ip address 34.1.1.3 255.255.255.0
 ip pim sparse-mode
 ip igmp version 3
 duplex auto
 speed auto
end
R4(config-if)#do show run int f0/0
interface FastEthernet0/0
 ip address 34.1.1.4 255.255.255.0
 ip pim sparse-mode
 ip igmp join-group 232.10.10.10 source 1.1.1.1
 duplex auto
 speed auto
end

R4(config-if)#do debug ip mpacket
IP multicast packets debugging is on
R4(config-if)#
*Mar  1 01:02:00.231: IP(0): s=1.1.1.1 (FastEthernet0/0) d=232.10.10.10 id=25, ttl=252, 

prot=1, len=114(100), mroute olist null