Re: How many replies to expect from ping multicast group

When testing my Multicast in the lab exam, I always take a few extra
seconds to do an extended PING in order to avoid any ambiguities and
ensure I remember to set the source interface.

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Senior CCIE Instructor
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On Apr 19, 2009, at 2:24 AM, Vinny wrote:

> 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 - 11:11:52 ART