From: Bob Sinclair (bsin@cox.net)
Date: Sat Oct 23 2004 - 17:06:18 GMT-3
Tim,
It is important to have the MA at the hub if you are distributing the
224.0.1.40 group in dense mode. NBMA-mode is not effective for dense mode
flows, since dense mode does not send the *,G entries that NBMA-mode relies
upon to populate the OIL.
The prune-override function of nbma-mode is well-documented, but its ability
to overcome the hub-and-spoke-OIL problem is not, IMHO.
We lab this up in NMC-1 class, and it is our experience that the multipoint
interface must be on the path to the RP if nbma-mode is going work to allow
sparse-mode flows into and back out of the hub on the same multipoint
interface.
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "Bob Sinclair" <bsin@cox.net>; "AK Singh" <singh.anand@gmail.com>;
"Cisco certification" <ccielab@groupstudy.com>
Sent: Saturday, October 23, 2004 2:34 PM
Subject: Re: Multicast over NBMA
> Hi Bob,
>
> I'm not sure we're saying different things. I was going by what Beau
> Willianson wrote in his book Developing IP Multicast networks on page
> 458 -
> 460.
>
> In his example, the RP is behind a spoke router, but the MA is behind the
> hub router. The network is, of course, running Auto-RP.
>
> With the RP behind one of the spoke routers, the other spoke routers don't
> hear the rp annouce messages from the rp, but the MA behind the hub does.
> And, since the MA then sends out the rp to group mappings, all the spoke
> routers hear them. Is this not correct?
>
> And, when the hub is configured with ip pim nbma mode, joins and prunes
> from
> the spoke routers don't affect joins and prunes from other spoke routers.
>
> Have anything changed since this was written or am I mis-understanding
> something critical?
>
> Tim
>
> ----- Original Message -----
> From: "Bob Sinclair" <bsin@cox.net>
> To: "ccie2be" <ccie2be@nyc.rr.com>; "AK Singh" <singh.anand@gmail.com>;
> "Cisco certification" <ccielab@groupstudy.com>
> Sent: Saturday, October 23, 2004 12:07 PM
> Subject: Re: Multicast over NBMA
>
>
>> 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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