From: Carter, Lee (Lee.Carter@CommerceBank.com)
Date: Tue Oct 07 2003 - 10:14:34 GMT-3
Enabling PIM Nonbroadcast Multiaccess Mode
PIM nonbroadcast multiaccess (NBMA) mode allows the Cisco IOS software to
replicate packets for each neighbor on the NBMA network. Traditionally, the
software replicates multicast and broadcast packets to all "broadcast"
configured neighbors. This action might be inefficient when not all
neighbors want packets for certain multicast groups. NBMA mode enables you
to reduce bandwidth on links leading into the NBMA network, and to reduce
the number of CPU cycles in switches and attached neighbors.
Configure this feature on ATM, Frame Relay, Switched Multimegabit Data
Service (SMDS), PRI ISDN, or X.25 networks only, especially when these media
do not have native multicast available. Do not use this feature on
multicast-capable LANs (such as Ethernet or FDDI).
You should use PIM sparse mode with this feature. Therefore, when each join
message is received from NBMA neighbors, PIM stores each neighbor IP address
and interface in the outgoing interface list for the group. When a packet is
destined for the group, the software replicates the packet and unicasts
(data-link unicasts) it to each neighbor that has joined the group.
To enable PIM NBMA mode on your serial link, use the following command in
interface configuration mode:
Command Purpose
Router(config-if)# ip pim nbma-mode Enables PIM NBMA mode.
Consider the following two factors before enabling PIM NBMA mode:
If the number of neighbors grows, the outgoing interface list gets large,
which costs memory and replication time.
If the network (Frame Relay, SMDS, or ATM) supports multicast natively, you
should use it so that replication is performed at optimal points in the
network.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr
_c/ipcpt3/1cfmulti.htm#1002080
You have to scroll up a few lines!
Pulled directly from Cisco's web site:
-----Original Message-----
From: SANCHEZ-MONGE,ANTONIO (HP-France,ex2)
[mailto:antonio.sanchez-monge@hp.com]
Sent: Tuesday, October 07, 2003 7:32 AM
To: 'ccielab@groupstudy.com'
Subject: Multicast in NBMA
Hi All,
Nice to meet you. I am beginning to prepare CCIE lab.
Could you please help me with this problem?
My topology: Frame-relay multipoint
r2 192.168.30.2(lo0 = 192.168.2.2)
/ / \
/ / \
/ / \
/ / \
(r4)(r3) (r5)
|________|
OSPF is running everywhere, every router can ping the others' loopbacks.
Also PIM Sparse-Dense is running everywhere.
The frame-relay maps are all configured for broadcast.
The Ethernet interface of r3 (192.168.20.3) and r2 loopback (192.168.2.2)
are multicast group 225.6.7.8 receivers.
When the multicast sender is r4, only r2 replies, whereas if it is r2 the
sender, r3 replies too.
I think this has to do with the multipoint architecture, but I cannot see
how to get a reply from r3 r4 (or how to get r2 forwarding the multicast
packet originated by r4 to r3). Any clues?
r2#sh ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected,
L - Local, P - Pruned, R - RP-bit set, F - Register flag,
T - SPT-bit set, J - Join SPT, M - MSDP created entry,
X - Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD, I - Received Source Specific Host Report
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 224.0.1.40), 00:44:09/00:00:00, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Serial0/0.30, Forward/Sparse-Dense, 00:44:09/00:00:00
(*, 225.6.7.8), 00:15:22/00:00:00, RP 0.0.0.0, flags: DCL
Incoming interface: Null, RPF nbr 0.0.0.0
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:07:56/00:00:00
Serial0/0.30, Forward/Sparse-Dense, 00:15:22/00:00:00
(192.168.2.2, 225.6.7.8), 00:00:07/00:02:52, flags: CLT
Incoming interface: Loopback0, RPF nbr 0.0.0.0
Outgoing interface list:
Serial0/0.30, Forward/Sparse-Dense, 00:00:10/00:00:00
(192.168.30.4, 225.6.7.8), 00:02:57/00:00:03, flags: CLT
Incoming interface: Serial0/0.30, RPF nbr 192.168.30.4
Outgoing interface list:
Loopback0, Forward/Sparse-Dense, 00:02:57/00:00:00
r2#i
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static
route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.30.0/24 is variably subnetted, 4 subnets, 2 masks
O 192.168.30.4/32 [110/64] via 192.168.30.4, 00:30:40, Serial0/0.30
O 192.168.30.5/32 [110/64] via 192.168.30.5, 00:30:40, Serial0/0.30
O 192.168.30.3/32 [110/64] via 192.168.30.3, 00:30:40, Serial0/0.30
C 192.168.30.0/28 is directly connected, Serial0/0.30
192.168.4.0/32 is subnetted, 1 subnets
O 192.168.4.4 [110/65] via 192.168.30.4, 00:30:40, Serial0/0.30
192.168.2.0/32 is subnetted, 1 subnets
C 192.168.2.2 is directly connected, Loopback0
192.168.3.0/32 is subnetted, 1 subnets
O 192.168.3.3 [110/65] via 192.168.30.3, 00:30:41, Serial0/0.30
Thanks & Cheers,
Antonio.
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