Pim NBMA Mode

On the following example. A server is multicasting over a NBMA network. There is only one member of the group on R1. Pim sparse mode is configured on ethernet and serial line. R2 is the manual RP for every groups.


R1
ip multicast-routing
ip pim rp-address 150.1.2.2

interface Serial1/0
ip address 132.1.0.1 255.255.255.0
ip pim sparse-mode

interface fa0/0
ip address 132.1.17.7 255.255.255.0
ip pim sparse-mode
ip igmp join-group 228.28.28.28

R2
ip multicast-routing
ip pim rp-address 150.1.2.2

interface Serial1/0
ip address 132.1.0.2 255.255.255.0
ip pim sparse-mode

interface fa0/0
ip address 132.1.6.6 255.255.255.0
ip pim sparse-mode

int lo0
ip address 150.1.2.2
ip pim sparse-mode

R3
ip multicast-routing
ip pim rp-address 150.1.2.2

interface Serial1/0
ip address 132.1.0.3 255.255.255.0
ip pim sparse-mode

interface fa0/0
ip address 132.1.18.8 255.255.255.0
ip pim sparse-mode

The result of debug mpacket on R3 & R1 when a ping is done from r2 ethernet interface show that the packet is received from both R1 & R3

Rack1R3#*Mar 1 02:26:59.307: IP(0): s=132.1.6.6 (Serial1/0) d=228.28.28.28 id=298, ttl=
253, prot=1, len=104(100), mroute olist null

Rack1R1#*Mar 1 02:27:57.951: IP(0): s=132.1.6.6 (Serial1/0) d=228.28.28.28 (FastEtherne
t0/0) id=298, ttl=253, prot=1, len=100(100), mforward

R2 mroute shows that the OIL is s1/0 so the mcast packet is replicated on every dlci attached to s1/0:

(132.1.6.6, 228.28.28.28), 00:03:13/00:01:48, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 132.1.26.6
Outgoing interface list:
Serial1/0, Forward/Sparse, 00:03:13/00:03:22

In order to avoid that use the PIM nbma-mode on R2 s1/0 interface:

interface s1/0
ip pim nbma-mode

Now, the result of debug mpacket on R3 & R1 when a ping is done from r2 ethernet interface show that the packet is received only on R1 as R3 doesn't have members.

Rack1R3#

Rack1R1#*Mar 1 02:27:57.951: IP(0): s=132.1.6.6 (Serial1/0) d=228.28.28.28 (FastEtherne
t0/0) id=298, ttl=253, prot=1, len=100(100), mforward

And R2 mroute shows that the OIL has now the the output interface s1/0 and the IP of the PIM neighbor so the mcast packet is only sent to this neighbor :

(132.1.6.6, 228.28.28.28), 00:00:16/00:03:17, flags: T
Incoming interface: FastEthernet0/0, RPF nbr 132.1.26.6
Outgoing interface list:
Serial1/0, 132.1.0.1, Forward/Sparse, 00:00:15/00:03:14


Remarks : when debugging with debug ip mpacket it's important to disable mroute-cache on every interface, otherwise only the first packet will be seen.