From: Robert Yee (robert@bluespud.com)
Date: Fri May 09 2003 - 13:11:59 GMT-3
Hi Danny,
Thanks for the reply. I do understand exactly what yo uare talking about. I've read through 4 differnt versions of the link that you have provided previously. All the docs use the identical examples, that is why I asked whether of not Auto-RP in an NBMA enviroment should be set up for 'sparse-dense' or 'sparse'. From what I have read, Auto-RP and IP PIM NBMA-MODE seem contrary to each other when it comes to the PIM mode:
IP PIM NBMA-MODE:
In order to deal with the problems introduced by NBMA networks, it is necessary to provide the router with information about the underlying L2 topology of the nbma network. Cisco IOS accomplishs this with the following interface command:
ip pim nbma-mode
In order forthis command to run correctly, SPARSE MODE MUST BE IN USE...The reason has to to with the sparse mode join message...
AUTO-RP:
A prerequisite for Auto-RP is that all interfaces must be configured in SPARSE-DENSE mode...
Both descriptions are very clear as to excactly what mode they need to run in, respectively. Yet they both seem contrary to each other. This is where my confusion is.
I'm still stuck with the question. Which mode do I configure if I'm using Auto-RP in a NBMA environment.
Thanks,
Robert
-----Original Message-----
From: Donny MATEO [mailto:donny.mateo@sg.ca-indosuez.com]
Sent: Friday, May 09, 2003 2:29 AM
To: Robert Yee
Cc: ccielab@groupstudy.com; nobody@groupstudy.com
Subject: Re: Auto-RP with NBMA
Hi Robert,
the real problem of this hub and spoke with the relation with RP and MA placing has nothing to do with the configuration of the mode of PIM.
The issue is (if I can remember correctly) that a router pass on Discovery message in a flooding fashion. Meaning it wont' pass it up to the interface it's receiving the information from.
So in your case, the MA must be put in the Hub or somewhere up stream of the hub router. If you places MA in one of the spoke, what will happen is the spoke router will flood the discovery message (the rp mapping) to the hub. And the hub will flood it to
it's other interface(s) except the one it received the message from. In this case the other spoke router will never get the rp discovery message and thus will not have any rp - group mapping information.
About ip pim nmba-mode, actually this is only an optimization method, does not really has anything to do with mode and rp or ma placement. You see to understand the problem you need to understand how router works on nbma network. When one router (say hub)
want's to send multicast traffic to nbma network, it's using a technique called pseudobroadcast (basically it's just the data link layer of a router replicate the packet and send them one by one to the peer(s) in the NBMA network. requiring peer_number x
resources that he need when doing it in a broadcast network (such as ethernet). Now this is not good. Specially in sparse mode. Since in sparse mode node will explicitly tells the upsteam (by sending join/prune message) when it has a downstream multicast,
client. So here the router behaves like dense mode and flood all the traffic downstream => bad for multicast, imagine movie streaming packet with 100 clients...urghh...
so what happen here you use the nbma feature of PIM, with this feature the router would track which peer in the nbma network that actually want's to receive the multicast traffic and only send them to those peer(s).
check this out if you're not clear
http://www.cisco.com/en/US/tech/tk828/tk363/technologies_white_paper09186a00800d6b61.shtml
Donny Mateo,
CCIE #11189
"Robert Yee"
<robert@bluespud. To: <ccielab@groupstudy.com>
com> cc:
Sent by: Subject: Auto-RP with NBMA
nobody@groupstudy
.com
05/09/2003 03:37
PM
Please respond to
"Robert Yee"
Hi All,
I've been reading about configuring Auto-RP and also Multicast over NBMA (in this case, frame-relay). All the literature point to these 2 things:
1. The use Auto-RP, the routers should be configured for 'sparse-dense-mode'
2. To use 'ip pim nbma-mode' accross a frame relay network, the routers should be configured for 'sparse' mode
So what if you want to configure Auto-RP over NBMA? All the stuff I read only points to where to place the MA, but does not say whether to use 'sparse-dense' or 'sparse'?
Can anyone shed some ligh on this?
TIA,
Robert
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