From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Oct 23 2004 - 12:24:25 GMT-3
The way I understand it, it's not the placement of the rp that matters as
far as reachability is concerned. It's the placement of the Mapping Agent.
Also, this issue is only relevant when running Auto-rp. It's not an issue
if using static rp or BSR.
You are correct about not needing a tunnel between the spokes when ip pim
nbma is running on the hub, but do you understand why that is?
In case you don't, here's the reason. Without ip pim nbma on the hub, when
a mcast stream starts flowing from the hub to the spokes assuming one spoke
wants the stream but the other spoke doesn't, the spoke that doesn't want
the stream sends a prune up to the hub.
Without nbma mode on the hub, the hub doesn't realize that one of the spokes
still wants the mcast stream. So, since the hub has only one interface to
reach both spokes and it now gets a prune message, it removes that interface
from the outgoing interface list (OIL) and stops the mcast stream from
reaching either spoke.
With nbma mode, the OIL contains both spokes. So, when the hub gets a prune
from just one of the spokes, it only removes that one spoke from it's OIL.
The other spoke continues to receive the mcast stream.
For more details on this, look for the mcast training presentations slides
on cisco.com
HTH, Tim
----- Original Message -----
From: "AK Singh" <singh.anand@gmail.com>
To: "Cisco certification" <ccielab@groupstudy.com>
Sent: Saturday, October 23, 2004 10:14 AM
Subject: Multicast over NBMA
> Hello folks,
>
> I know thie topic has been discussed in several ways on this alias. I
> searched but couldn't get a direct answer hence posting on this alias.
> Appreciate any response.
>
> Let us say we are running pim in sparse mode and we have take RP
> issues (i .e spokes are learning correct RPs, the RP is places a
> router which is on top of hub and we are using autorp listener).
>
> Now when to send a feed (ping to the group) from one of the spoke to a
> group on other spoke, do we always need a tunnel to be created between
> spokes for this?
>
> Here is my undestanding (please correct me), we don't need tunnel
> between spokes when we are using either:
>
> 1) pim nbma mode
> 2) spokes have brodcast capability between them.
>
> When else do we need? Any more lights on this topic.
>
> Thanks
> -Anand
>
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