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New Member

PIM Sparse-dense mode


I had some trouble with the multicast (the scheme is in attachements). The trouble is that I can't ping group on SW4 from another router. I found that multicast packets arrive to SW4 (I've watched with sniffer). And SW4 increase the counter of that packets. I can see it with the command 'sh ip mroute count'. But ICMP Echo Reply don't send. And multicast traffic can't be found on SW4 with 'debug ip mpacket'. The switch is 3750.

Could you please explain what I've done wrong?

Everyone's tags (3)
New Member

Re: PIM Sparse-dense mode


I've found the problem. Switch doesn't correctly process multicast traffic when the command 'ip pim spt-threshold 128' was issued and the traffic is below 128 kbps. It means it doesn't process multicast on shared tree. But at the same time I can see that multicast traffic on the physical port of this switch (with SPAN and sniffer). When the command 'no ip pim spt-threshold' was issued switch processes the multicast traffic correctly. It means that when the switch is on SPT everything is OK.

This problem was appeared with IOS 12.2(46)SE, 12.2(50)SE3, 12.2(53)SE2. Unfortunately I haven't found the IOS with which this issue doesn't appear.

Hall of Fame Super Silver

Re: PIM Sparse-dense mode

Hello Kondratev,

>> t means it doesn't process multicast on shared tree

Actually, it is the opposite the command ip pim spt-threshold 128 causes the device to stay on the shared tree that is the tree rooted at the RP, that is called also RPT, until a group traffic is below 128 kbps.

SPT means source based tree. These acronyms are a little misleading.

However, you have been kind to provide feedback on your issue

this may help somebody else that may have the same problem

Hope to help