From: Wolfgang Marschner (wmarschner@web.de)
Date: Fri Sep 02 2005 - 15:17:25 GMT-3
Hi,
this is a normal behaviour with Multicast over NBMA.
It works with "pseudobroadcast", that means, by replicating
the packets on the hub to the spoke VC's, when broadcast is
enabled per auto-mapping ( inverse-arp ) or manual mapping
( frame-relay map IP-address dlci DLCi-number braodcast ).
The hub must pseudobroadcast because of the split horizon rule,
but that can be only done on layer 2 with process-switching on
a router.
To override this behavior, configure on the hub interface the
command "ip pim nbma-mode".
Now the hub router can replicate the packets on layer 3
with fast-switching.
When you take a look in the Multicast routing table you will
notice, that every spoke-connection joined for a multicast
group will appear as a seperate entry in the
Outgoing Interface List ( OIL ).
For that reason, no more problems will noticed, when a spoke
router leaves a multicast-group while working in PIM DM.
Hope that helps.
W. Marschner
CCIE #8232
----- Original Message -----
From: "Duongla" <duongla@vnn.vn>
To: <ccielab@groupstudy.com>
Sent: Friday, September 02, 2005 7:15 PM
Subject: Multicast forwarding fails with fast switching but OK with
process.Can U help?
> Hi group,
>
> I have tried the following scenario on 4 Cisco 2600:
> R1,R2 and R3 are connected via multipoint frame-relay (physical
> interface), R2
> is the HUB.
> Routing is running normally, all routers can reach all subnets.
> R2 f0/0 connect to R4 whichs is a test router, responsible for genarating
> multcast traffic.
> R1,R2,R3 are all configured with multicast PIM sparse mode and loopback
> interface of R3
> is configured manually on 3 routers as RP.
> R1f0/0 and R3 f0/0 are configured to join group 239.1.1.1
> Before PING 239.1.1.1 from R4, the mroute tables int 3 router are in
> normal
> state:
> R1,R3 send Join msg to RP which is R2, so R2 has a (*,239.1.1.1) entry in
> its
> mroute table.
> For first PING 239.1.1.1 from R4, both R1 and R3 reply.
> From second PING, just R3 replies.
> Do debug ip mpacket fastswitch 239.1.1.1, I saw R2 forwarded the mcast
> packet
> from R4 out serial0/0
> (the frame relay port, connecting to R1 and R3) but just R3 got the packet
> and
> sent PING echo-reply.
> One interesting notice is: router with higher IP address of frame relay
> interface receives the PING mcast packet.
> In this case R3.
> If I turn off fast switching on R2 s0/0 then both R1 and R3 receive mcast
> packet.
>
> Can anyone help clarify the above behaviour ?
> Thanks in advance.
> Duongla
>
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