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Multicast:Understanding output from mtrace

Answered Question
Oct 7th, 2009
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Folks, application folks in my company complain that multicast traffic for a group 239.254.13.31 does not work. They say that traffic for group 239.254.13.32 works OK. I do mtrace from Layer 3 switch and the difference I notice is that the last path (-4 10.12.17.3) is not listed for the 239.254.13.31. Can someone confirm what I can infer from this mtrace output?


switchL3#mtrace 10.12.17.3 10.12.49.15 239.254.13.32

Type escape sequence to abort.

Mtrace from 10.12.17.3 to 10.12.49.15 via group 239.254.13.32

From source (?) to destination (?)

Querying full reverse path...

0 10.12.49.15

-1 10.12.49.60 PIM [10.12.17.0/26]

-2 10.12.60.105 PIM [10.12.17.0/26]

-3 10.12.60.61 PIM [10.12.17.0/26]

-4 10.12.17.3

switchL3#mtrace 10.12.17.3 10.12.49.15 239.254.13.31

Type escape sequence to abort.

Mtrace from 10.12.17.3 to 10.12.49.15 via group 239.254.13.31

From source (?) to destination (?)

Querying full reverse path...

0 10.12.49.15

-1 10.12.49.60 PIM [10.12.17.0/26]

-2 10.12.60.105 PIM [10.12.17.0/26]

-3 10.12.60.61 PIM Prune sent upstream [10.12.17.0/26]

switchL3#


Correct Answer by Edison Ortiz about 7 years 10 months ago

Option 2 allows you to map different source|group pairs thus it is more scalable. With that said, to keep things simple, go with Option 1 for your current setup.


Regards,


Edison.

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Edison Ortiz Wed, 10/07/2009 - 13:52
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10.12.17.3 is not sending to 239.254.13.31 multicast group.


10.12.17.3 is only sending to 239.254.13.32.

__


Edison.

news2010a Wed, 10/07/2009 - 14:22
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Great. On each of those PIM hops listed, I see the entry:

!------

ip igmp ssm-map static ssm-source1 10.12.17.3

!

ip access-list standard ssm-source1

permit 239.254.13.32

!-----


I see I have two options to accomodate this. Do you see any need or advantage in doing Option 2) below?


Option 1)


ip access-list standard ssm-source1

permit 239.254.13.31


or


Option 2)


ip igmp ssm-map static ssm-source2 10.12.17.3

!

ip access-list standard ssm-source2

permit 239.254.13.31


Correct Answer
Edison Ortiz Wed, 10/07/2009 - 14:30
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Option 2 allows you to map different source|group pairs thus it is more scalable. With that said, to keep things simple, go with Option 1 for your current setup.


Regards,


Edison.

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