From: Timothy Chin (Tim@1c-solutions.com)
Date: Thu Mar 06 2008 - 16:01:39 ARST
I believe you would have to add a static multicast route for this
scenario.
Router 4 would have something like:
Ip mroute 0.0.0.0 0.0.0.0 E0
Otherwise the RPF check would fail if I'm not mistaken.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Reza Toghraee
Sent: Thursday, March 06, 2008 3:47 AM
To: ccielab@groupstudy.com
Subject: Multicast RPF check Question
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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