多播静态路由引起的循环问题的解决(1)

一、问题

在r3和r1之间使用了GRE通道，所有的路由器接口配置为sparse-mode,R4 ip为（1.1.4.4）但Ｒ１无法ping通多播源。
二、示意图如下

multicast source -----R5------R3-------R223----R1--e0
............................................|
............................................|
............................................R4
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
三、原配置如下
R1#mtrace 1.1.15.1 150.100.2.1 239.255.8.8
Type escape sequence to abort.
Mtrace from 1.1.15.1 to 150.100.2.1 via group 239.255.8.8
From source (?) to destination (?)
Querying full reverse path...
0 150.100.2.1
-1 1.1.12.5 PIM [default]
-2 1.1.12.3 PIM [default]
-3 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-4 1.1.16.3 PIM [default]
-5 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-6 1.1.16.3 PIM [default]
-7 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-8 1.1.16.3 PIM [default]
-9 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-10 1.1.16.3 PIM [default]
-11 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-12 1.1.16.3 PIM [default]
-13 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-14 1.1.16.3 PIM [default]
-15 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-16 1.1.16.3 PIM [default]
-17 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-18 1.1.16.3 PIM [default]
-19 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-20 1.1.16.3 PIM [default]
-21 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-22 1.1.16.3 PIM [default]
-23 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-24 1.1.16.3 PIM [default]
-25 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-26 1.1.16.3 PIM [default]
-27 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-28 1.1.16.3 PIM [default]
-29 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-30 1.1.16.3 PIM [default]
-31 1.1.16.4 PIM Reached RP/Core [1.1.15.0/24]
-32 1.1.16.3 PIM [default]