From: Vinoth Kannan Ganapathy (ccieprep4vinoth@gmail.com)
Date: Thu Mar 06 2008 - 19:20:39 ARST
Hi,
I beleive, when are there are two routes to the source,
RPF will be elected based on the highest IP address of the neighbour.
Based on tht if your R3's IP address is the highest then it has been choose
as the RPF neighbour..
Thx and regds
VInoth G
On 3/6/08, Reza Toghraee <reza@toghraee.com> wrote:
>
> Hello
>
> I'm a little confused about how RPF happens where there are 2 routes
> through
> the source.
> Ospf is running in this diagram
> R1 is attacxhed to multicast rource
> PIM DENSE mode is in USE
> AlL interfaces Except the R3 S0 have "ip pim dense-mode" command. (R3 S0
> not in Multicast)
> R4 has 2 routes to source, through R2 and R3 (via OSPF)
> Assume that the metric of S0 on R3 and E0 on R2 are same.
>
>
> R2 E0 : 172.16.21.2/24
> R2 E0 : 172.16.31.3/24
>
>
> ---------------
> | R1 |
> |att to SRC |
> ---------------
> S0 E0
> / \
> / \
> / \
> / \
> -------- -----------
> | R2 | |
> R3 |
> | |
> | |
> --------
> ------------
> E0|
> |S0
> \
> /
> \
> /
> \
> /
> \
> /
> \
> /
> ----------------
> | R4
> |
> |
> |
>
> ---------------
>
> Now the question is about the RPF check in R4.
> When R4 receives a multicast packet from R2 E0, it checks the unicast
> routing, finds 2 routes, but it can only select 1 route (as I understood),
> But what is the RPF neighbor for R4? It is R3 or R2? It depends on
> neighbor
> IP , neighbor metric , neighbnor interface ?
> I search in last posts, I found that Scott wrote to use Ip Multicast
> multihop, and it fixes the problem but I donno what is this command.
> Also I know with static multicast route we can solve it, I;m looking to
> know
> when R4 selects R2 as RPF neighbor and when R3 ?
>
>
> Thanks
> Reza
>
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