Troubleshooting multicast sparse Mode

Multicast traffic always send to group address, never from

IGMP (router to client communication)
IGMP testing commands - simulate multicast receiver

• ip igmp join-group - response icmp echo, process switching mpackets
• ip igmp static-group - not response icmp echo

PIM – Protocol Independent Multicast - Router to router communication

Sparse Mode or Dense modes - this ONLY affect the traffic SENDING OUT interface; an interface will always receive multicast traffic once enble either "ip pim XXX mode".  

Sparse Mode process:

multicast server - [S,G] fisrt hop router - unicast - RP - [*,G] - last hop router - receiver
multicast server - [S,G] fisrt hop router - [S,G] - RP - [*,G] - last hop router - receiver
multicast server - [S,G] fisrt hop router - [S,G] - last hop router - receiver 




Useful command:


ip igmp join-group multicast-address - simulate a join host

sh ip mr multicast-address - check [S,G] and [*,G]

sh ip mr count - check multicast traffic stats, look for failures such as rpf or oil-null

sh ip rpf source-ip-address

Reference: IPEXPERT
Basic Multicast Troubleshooting Tools 
IP Multicast Troubleshooting Guide 
IP Multicast Routing Commands