From: Pavel Bykov (slidersv@gmail.com)
Date: Tue Nov 18 2008 - 18:40:01 ARST
Hello.
Frame Relay does not support broadcast, ever. It is by design a
non-broadcast multiple access technology.
What routers do is packet replication, when they take a copy and send one to
every destination.
The difference is in function. While in broadcast medium, like Ethernet,
only one packet has to be sent, and Ethernet technology would deliver it to
everybody. On frame relay broadcast has to be essentially turned into
replicated unicast.
This has in turn a big effect on PIM function. Normally one spoke would send
packet directly to the other spoke, but now it has to come in the interface
of a hub and leave out the exact same interface! PIM is designed around RPF,
and this exactly breaks this rule.
So what now? This is where NBMA mode comes into play. NBMA mode creates
something like virtual output entries in OIL by adding IP address to the
interface, this way you have an entry in OIL for every spoke, so RPF will
not fail, because output interface now is not just S0/1 for examply, but
something like S0/1 10.0.0.1
Alternatively you can use suninterfaces to create point-to-point links,
tunnels, PPPoFR, etc.
NBMA mode could also be used in QinQ environment.
As a side not, "ip ospf network broadcast" does not relate to this. Ofcourse
unicast routing has to work before you start with multicast, but what kind
of OSPF netowkr you use does not matter. You can drop OSPF altogether, and
use RIP, STATIC, BGP, IS-IS, EIGRP, PBR, ODR or really, whatever you like.
On Tue, Nov 18, 2008 at 5:34 PM, Zealist Hammad <zealist@gmail.com> wrote:
> Hies,
>
> I have a scenario I config FR BroadCast network(config ip ospf network
> broadcast) and config multicasting then config RP over one of spokes
> also Join IGMP group on same router then
> topology is like R3-----R1 -----R4
>
> 1- if runing PIM sparse-mode do we need to config command at hub
> ip pim nbma-mode??
> 2- Same question for sparse-dense mode.
>
> If i make RP at Hub it works fine without nbma-mode command over sparse
> mode
> but if RP is also at spoke i dont get ping reply from other spokes.
>
> regards
>
>
> --
> zealist@gmail.com
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-- Pavel Bykov ------------------------------------------------- Stop the braindumps! http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
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