From: Salau, Yemi (yemi.salau@siemens.com)
Date: Tue Dec 04 2007 - 07:05:17 ART
Basically, ip pim autorp listener is basically telling the router to
flood multicast traffic for 2 auto-rp groups 224.0.1.39 and 224.0.1.40
across interfaces operating in PIM sparse mode. I believe you know cRPs
uses 224.0.1.39 to announce/advertise themselves to the MA, and in turn
the MA routers receive these multicasts, and periodically advertises
this information to multicast group 224.0.1.40
The thing is, before MA routers can join 224.0.1.39, then need to know
who the RP for that group is, also, before multicast routers can join
224.0.1.40 to receive the RP information from MAs, they need to know who
the RP for 224.0.1.40 is. Hence the old recursive design flaw within
multicast technology. Before users join a group, they need who the RP
is, and before they know who the RP is they need to joing the group.
Hence, why some techies use sparse-dense-mode, so that for those groups
which you don't know who the RP is, you just switch to dense mode to
flood the traffic, (eg. cRPs using flooding of traffic to group
224.0.1.39, and MAs using flooding of traffic to group 224.0.1.40)
Another way to do this is to use sparse-mode (which you did), but ip
auto-rp listener is disabled by default now, so you have to enable it to
tell routers to turn on "DENSE" mode operation for only the 2 AUTO-RP
groups ... 224.0.1.39 and 224.0.1.40.
Your RPs need to flood 224.0.1.39 traffic to MAs, so MAs have to join
that group, since they don't know who the RP is for 224.0.1.39, they
then operate the group in dense mode. Similarly, your other multicast
routers should join the 224.0.1.40, and understand how to flood the
224.0.1.40 traffic as well in case there are downstream routers who need
the information. Since they don't know who the RP for 224.0.1.40 is,
they then operate the group in dense mode.
NOTE: ip auto-rp listener doesn't flood traffic for all multicast groups
there is, only for the auro-rp groups.
So to answer your question in a single statement:- YES, you need to do
ip auto-rp listener for R3 and R5, if you're using sparse-mode and
auto-rp for them. If you don't want to use auto-rp, then just use
static-rp then (hardcoding who the RP is to them)
Many Thanks
Yemi Salau
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Gupta, Gopal (NWCC)
Sent: Tuesday, December 04, 2007 9:25 AM
To: nhatphuc; Cisco certification
Subject: RE: IP PIM AutoRP Listener placement?
In my opinion you don't need coz, R1 will flood through dense mode abt
RP and further R4 will do the same; provided that IP pim auto RP is
configured on R1,R4 and R2 so, There should be no problem for R5 to
accept that info about the RP.
HTH
Gops
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
nhatphuc
Sent: Tuesday, December 04, 2007 14:44
To: Cisco certification
Subject: IP PIM AutoRP Listener placement?
Importance: Low
Hi Group,
My topology is like this:
R1------R2-----R3
|
|
R4
|
|
R5
PIM Sparse Mode is configured. R1 is Mapping Agent, R2 and R4 are cRP. I
choose to use ip pim autorp listener.
My opinion is: No need to configure ip pim autorp listener on R3 and R5.
My question: Do you have the same idea as me? Why/Why not?
Thank you
Phuc
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