From: The Great Ryan (pv.ryan@gmail.com)
Date: Sat Oct 15 2005 - 11:29:13 GMT-3
Hi,
R1(ip igmp join-group)--R2(multicast source)--R3(RP)
When R2 act as multicast source, it will contact RP(R3) and then forward to R1
i.e. R2 -> R3 -> R1
Then it will switch to SPT
i.e R2 -> R1
Thus, I want to know where "ip pim spt-threshold infinity" should be needed?
in R2 ? in R1?
Ryan
2005/10/15, Carl Willias <mandingo2073@yahoo.com>:
> I assume you mean the infinity option. the answer is that it depends. Your topology does not really have an spt :-). But in reality you would put the command on every router up to the RP. Think of it like this, multicast will stay on the shared tree until a router that finds it has a shorter path to the multicast source, this box needs to be told to ignore your routing table that says if has a better way to get the the source and keep the tree back to the RP. That router has to have the ip pim spt-threshold command. In essence the choice to stay or leave the shared tree is a router by router choice. If you know the point that those tree diverge you can get away with putting it on one box. But it is sound practice in the real world to put it along the whole shared tree
>
> CW
>
> ----- Original Message ----
> From: The Great Ryan <pv.ryan@gmail.com>
> To: Cisco certification <ccielab@groupstudy.com>
> Sent: Saturday, October 15, 2005 6:21:04 AM
> Subject: Where I should place "ip pim spt-threshold " ?
>
>
> Hi Group
>
> R1--R2--R3
>
> R1 is RP
> R3 is running "ip igmp join-group" on its loopback interface
>
> Where I should place "ip pim spt-threshold " such that it will never
> switch to shortest-path tree?
>
> Place this command only on R2 or all of them ?
>
> Thanks!
> Ryan
>
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