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Ping test for SSM Multicast, valid or not?

I'm refreshing my knowledge on multicast in prep for a CCIE SP lab, and am currently working on SSM.

 

The short question is:

If I have a working SM multicast network using static RP's and can ping a receiver from the source when the receiving host has joined the group should the same be true for a working multicast network configured to use SSM instead of an RP?

Is my ICMP test using a router as a source to ping a group address valid or not?

 

In more detail:

I set up a basic lab in GNS3 (as per the example in R+S CCIE Certification guide version 4, topology attached) starting with PIM-SM with static RP. I have routers simulating the source (R6) and the receiver (R7).

 

On my receiver I configure the ip igmp join-group 232.1.1.1 command, and from my source router can ping this group, so far so good.

Then I decided to investigate SSM, which I have never used before, using the same topology. I removed the static RP entries, added ip pim ssm default and ip igmp v3 to each interface in the core topology, plus the interfaces between the receiver and its first hop router.

On the receiver I then removed the join group command, replacing it with  ip igmp join-group 232.1.1.1 source 10.4.7.7. The IOS guide indicates that this command provides the IGMPv3  support.

Checking the next hop interface with wireshark I see an igmpv3 join/group message for the new source. That router (R4) generates an mroute entry as follows:

(10.4.7.7, 232.1.1.1), 00:11:57/00:02:12, flags: sPTI
  Incoming interface: Ethernet1/0, RPF nbr 0.0.0.0
  Outgoing interface list: Null

 

There is no mroute entry on R1 which is closest to the source

 

But, now I'm unable to ping the group address from the source. This test worked when using static RP's.

 

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