R1:
ip multicast-routing----开启多播模式
inter lo 0
ip pim spare-mode
inter fa0/0
ip pim sparse-mode
inter s1/0
ip pim spare-mode
ip pim rp-candidate lo 0-----R1为：C-RP（候选聚合点），lo 0为通讯地址。
R2:
ip multicast-routing
int lo0
ip pim sparse-modey
int fa0/0
ip pim sparse-mode
int s3/0
ip pim sparse-mode
ip pim rp-candidate lo0 pirorit 100-----RP默认优先级为0，值越小越优先
ip pim bsr-candidate lo0--------R2为：C-BSR（引导路由器），默认优先级为0，值越大越优先
SW1:
ip multicast-routing
int fa0/1
ip pim sparse-mode
int vlan 13
ip pim sparse-mode
SW2:
ip multicast-routing
inter vlan 12
ip pim sparse-mode
ip igmp join-group 236.1.1.1-----vlan 12 加入组236.1.1.1
inter vlan 13
ip pimn sparse-mode