From: Bob Sinclair (bsin@cox.net)
Date: Sat Oct 23 2004 - 13:07:00 GMT-3
Tim,
If you are saying that the placement of the RP is irrelevant to the
operation of PIM NBMA-mode in AK's scenario, then I beg to differ. If the
hub interface is not on the path between the spoke and the RP, then the hub
will not receive a *,G from that spoke, that spoke will not show up on the
hub's OIL, and it will not receive multicast traffic from another spoke.
Lab it up.
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "AK Singh" <singh.anand@gmail.com>; "Cisco certification"
<ccielab@groupstudy.com>
Sent: Saturday, October 23, 2004 11:24 AM
Subject: Re: Multicast over NBMA
> 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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