Multicast - Stub multicast routing and IGMP helper

Overview

Creating a multicast hub site is often done to address bandwidth and resource limitations for a given site. A hub site does not establish PIM adjacency with upstream neighbors thereby preventing the sending and receiving of PIM messages. In order to allow downstream receivers to join multicast groups and receive multicast traffic the upstream router to the stub router uses the ip igmp helper-address [upstream-router-IP] command along with enabling PIM DM on downstream receiver interfaces. The stub router enables PIM DM on its upstream and downstream interfaces but also configures the ip pim neighbor-filter [access-list] command to prevent PIM neighbor establishment.

Concepts tested

• Configure PIM Sparse and dense mode
• Create multicast stub router
• Configure ip igmp helper

Topology

Lab Tasks

• Configure PIM SM on all paths between R1 and the source router.
• Ensure the Reciever can join any multicast group but does not participate in PIM messaging or form any PIM neighbors
• Verify the configuration

GNS3 configuration file, requires IOS v15 for the 7200 router: Link


Solution

R1(config)#ip multicast-routing
R1(config)#int g0/0
R1(config-if)#ip pim sparse-mode
R1(config-if)#exit
R1(config)#int g1/0
R1(config-if)#ip pim dense-mode

R1(config-if)#ip igmp helper-address 2.2.2.2

R1(config-if)#ip igmp helper-address 3.3.3.3

R1(config-if)#exit

R2(config)#ip multicast-routing

R2(config)#int g0/0

R2(config-if)#ip pim sparse-mode

R2(config-if)#exit

R2(config)#int g1/0

R2(config-if)#ip pim sparse-mode

R2(config-if)#exit

R2(config)#int loopback 0

R2(config-if)#ip pim sparse-mode

R2(config-if)#exit

R2(config)#ip pim rp-candidate loopback 0

R3(config)#ip multicast-routing

R3(config)#int g0/0

R3(config-if)#ip pim sparse-mode

R3(config-if)#exit

R3(config)#int g1/0

R3(config-if)#ip pim sparse-mode

R3(config-if)#exit

R3(config)#int loopback 0

R3(config-if)#ip pim sparse-mode

R3(config-if)#exit

R3(config)#ip pim rp-candidate loopback 0

R4(config)#ip multicast-routing

R4(config)#int g0/0

R4(config-if)#ip pim sparse-mode

R4(config-if)#exit

R4(config)#int g1/0

R4(config-if)#ip pim sparse-mode

R4(config-if)#exit

R4(config)#int loopback 0

R4(config-if)#ip pim sparse-mode

R4(config-if)#exit

R4(config)#int s3/0

R4(config-if)#ip pim sparse-mode

R4(config-if)#exit

R4(config)#ip pim bsr-candidate loopback 0

Source(config)#ip multicast-routing

Source(config)#int g0/0
Source(config-if)#ip pim sparse-mode
Source(config-if)#exit

Receiver(config)#ip multicast-routing
Receiver(config)#ip access-list standard PIM_FILTER
Receiver(config-std-nacl)#deny 120.0.10.1
Receiver(config-std-nacl)#permit any
Receiver(config-std-nacl)#exit
Receiver(config)#int g0/0
Receiver(config-if)#ip pim neighbor-filter PIM_FILTER
Receiver(config-if)#ip pim dense-mode
Receiver(config-if)#ip igmp join-group 239.1.1.1

Receiver(config-if)#exit

Verification

Source#ping 239.1.1.1 rep 1000

Type escape sequence to abort.
Sending 1000, 100-byte ICMP Echos to 239.1.1.1, timeout is 2 seconds:

Reply to request 0 from 120.0.10.254, 140 ms
Reply to request 1 from 120.0.10.254, 168 ms
Reply to request 3 from 120.0.10.254, 184 ms

Receiver#sh ip igmp groups

IGMP Connected Group Membership

Group Address    Interface                Uptime    Expires   Last Reporter   Group Accounted

239.1.1.1        GigabitEthernet0/0       00:35:21  00:02:57  120.0.10.254

R1#sh ip mroute 239.1.1.1


(*, 239.1.1.1), 00:33:37/stopped, RP 2.2.2.2, flags: SJC
  Incoming interface: GigabitEthernet0/0, RPF nbr 120.0.0.2
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Dense, 00:03:37/00:00:00

(120.0.45.5, 239.1.1.1), 00:28:24/00:01:11, flags: T
  Incoming interface: GigabitEthernet0/0, RPF nbr 120.0.0.3
  Outgoing interface list:
    GigabitEthernet1/0, Forward/Dense, 00:03:37/00:00:00