How many replies to expect from ping multicast group address

Hi experts!

How many replies should I expect to get when i ping a multicast group?

This question has been bugging me for quite a while. Debug shows that the source (the router which issued ping command) is actually sending icmp echo request from all it's active interfaces - regardless of whether it is pim enabled.

More frustratingly, sometimes the reply numbers may vary in consecutive pings from the same router! (As below)

Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
..
Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
Reply to request 0 from 33.33.16.6, 128 ms
Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
Reply to request 0 from 33.33.16.6, 124 ms
Reply to request 0 from 33.33.16.6, 140 ms
Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
Reply to request 0 from 33.33.16.6, 152 ms
Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
..
Rack33R5(config-subif)#do ping 224.2.2.2
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 224.2.2.2, timeout is 2 seconds:
..
Rack33R5(config-subif)#

It seems have to do with one/some/all of the following factors
-number of active interface
-number of pim enabled interface
-number of receiver (router that's issued ip igmp join-group)
-number of RP
-number of FORWARDER
-network type (Ethernet/Frame-relay)
-Frame-relay interface type (P-2-P,P-2-M)
-PIM mode

I have tried with the following debug commands
debug ip icmp
debug ip pim auto-rp
debug ip pim df
access-list 101 permit icmp any host 224.2.2.2
debug ip packets 101

Could anyone show me a way of predicting the results?

Thanks a lot~

2009-04-19

Vinny

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Received on Sun Apr 19 2009 - 14:24:01 ART