From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Feb 05 2005 - 16:59:52 GMT-3
PS:
To be able to think through whether or not ip pim nbma-mode is needed, you
need to understand what nbma-mode does.
In brief, when ip pim is running on a router, pim itself doesn't know
whether or not a f/r interface is p2p or p2m because pim is a layer 3
process and f/r is a layer 2 process.
Therefore, unless you tell pim if the f/r interface is p2m by configuring
the nbma-mode, pim will treat the interface as a p2p interface and therefore
will add the interface to the incoming or oil as appropriate.
Let's assume that pim adds the f/r interface to the oil as a result of a
join from one of the spokes.
Now, after adding the f/r interface the oil, the hub router gets a prune
from one of the spokes. (Keep in mind that when this happens, the other
spokes don't hear this prune message.)
As a result of getting this prune message, the hub will remove the f/r
interface from the oil in accordance with normal sparse mode pim behavior.
Therefore, if any of the other spokes were receiving that mcast stream for
which the prune message was sent, all of sudden, they will stop getting that
mcast stream because the hub just removed the f/r interface from the oil.
This type of behavoir will wreck havoc in a auto-rp mcast network.
What is needed is for the hub to just remove that particular pvc from the
oil from which the prune message came - not all the pvc's.
To make the hub behave this way you use the nbma-mode. So now, when one
spoke sends a prune message, only that individual spoke is removed from the
oil, not all the spokes.
HTH, Tim
----- Original Message -----
From: "null void" <nullv0idmain@yahoo.com>
To: "Labcciee" <labccie@uol.com.br>; <ccielab@groupstudy.com>
Sent: Friday, February 04, 2005 12:19 PM
Subject: Re: Requirement details of "IP PIM NBMA"
> Intersting statements on the book you cited LabCCIE in the prac study 2
book on page 247 of the lab 6 prac lab , they are stating since R5 , R6 and
R13 are a multipoint frame network segment , all routers on there frame
relay interfaces have ip pim nbma-mode on them .. The way it is stated I am
assuming they are saying anytime you have a multipoint frame relay interface
and are running multicast to spoke routers use the nbma-mode command.. I was
under the impression we only needed it sometimes , such as when a hub /
multipoint router needs multicast streams to go to say 3 of its spoke
routers , in this situation I can see this .. But if I only have one spoke
that is multicast enabled I dont think it is required , the only thing I
have noticed is that since you dont put that command ip pim nbma-mode on the
hub when you ping multicast groups , assuming they are pingable , then you
only get 1 reply back I am assuming this is due to being fastswitched ??
>
> Labcciee <labccie@uol.com.br> wrote:Yes, thats the explanation I found in
the CCIE Practical Studies volume II.
> If one othe spoke routers request the hub to stop sending milticast
traffic to
> it, withou the command "ip pim nbma-mode" the others hub connected to the
same
> phisical interface will stop receiving multicast traffic too.
> If the others hub are not reciving any multicast trafficc, i think there
will
> be no problem.
>
>
> ----- Original Message -----
> From: null void
> To: Labcciee ; ccielab@groupstudy.com
> Sent: Friday, February 04, 2005 2:46 PM
> Subject: Re: Requirement details of "IP PIM NBMA"
>
>
> Thanks for the reply... I will read that section but on the docCD
>
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fip
> r_c/ipcpt3/1cfmulti.htm#21887
>
> the way they are explaining it is that the purpose of "ip pim nbma-mode"
is
> for efficiency of the link . So if your Multipoint Hub interface running
ip
> pim sparse-mode .. Has its framerelay interface maps configured with
broadcast
> feature on each map statement to say 4 spoke routers... ip pim nbma-mode
> reduces unneed traffic so if only spoke1 requested to join a group , ip
pim
> nbma-mode will when receiving traffic for that group send it to that one
> neighbor who requested it not to the other 3... But you are saying that if
one
> of the other spokes was receiving the stream earlier but then sent a
request
> to stop sending the stream then all spokes will now not receive the
multicast
> stream ?? What if your in a situation in which out of 3 spokes only 1 of
> those spokes has multicast enabled the other 2 do not have any muliticast
> configured on them at all , at that point it would not be needed then
correct
> ? Your saying that if multiple spokes are joined to a group , then one of
them
> says stop , it affects all spokes becuase they are all connected into the
HUB
> routers physical interface ??
>
> Null..
>
> Labcciee wrote:
> Hi,
>
> The "ip pim nbma-mode" must be configured on subinterfaces running frame
> relay multipoint mode.
> It's required because without it, with the reouter receives a prune
> message
> on the phisical interface it could cut off the multicast traffic for all
> others subinterfaces. This explanation is on the CCIE Practical Studies
> volume II
> ----- Original Message -----
> From: "null void"
> To:
> Sent: Friday, February 04, 2005 2:18 PM
> Subject: Requirement details of "IP PIM NBMA"
>
>
> > Say we have the following topology:
> >
> > R1 - is the hub of frame relay hub-spoke toplogy. Serial 0/0.1
> multipoint
> goes to 2 spoke routers R2 , R3. Serial 0/1.1 point-to-point goes to R6's
> S0/1 this is frame-relay circuit also
> >
> > R6 - is a standalone stub router with a point to point se rial sub
> interface off of Ser0/1 to R1's S0/1
> >
> > R3 - Ser0/0 physical interface connects into R1 the frame relay hub
> router's s0/0.1 multipoint so R3 , R2 and R1 are all layer 3 reachable on
> same ip subnet in hub spoke topology.
> >
> > If we configure say R3 as RP on its loopback 0 interface for all
> groups.
> Then configure ip pim sparse-mode on all interfaces of R3 , R6 , R1 . So
> now
> R3 , R6 and R1 see each other as pim neighbors and the RP is found being
> hardcoded to R3 loopback . Is IP PIM NBMA mode required on R1's S0/0.1
> multipoint and s0/1.1 point to point interfaces ?? Without it I can still
> from all multicast enabled routers , in this case being R3 , R6 and R1
> ping
> the groups that we configured onto R6's Loopback 0 interace via the ip
> igmp
> join-group x.x.x.x command so it is working ... But my question is when
> is
> ip pim nbma requried and why ??? Any resources / docs on this would be
> greatly appreciated... TIA Null
> >
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