From: Reza Toghraee (reza@toghraee.com)
Date: Thu Mar 06 2008 - 06:46:41 ARST
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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