Multicast Service Reflection

Multicast service reflection feature enables the users to translate externally received multicast destination addresses to addresses that conform to the organization's internal addressing policy. With this feature, users need not redistribute routes at the translation boundary into their network infrastructure for the Reverse Path Forwarding (RPF) to work properly. Also, users can receive identical feeds from two ingress points in the network and route them independently.

The multicast service reflection feature is configured on the virtual interface. When a packet is forwarded to a virtual interface (original IP), this feature maps the original IP address to an internal IP address and the traffic is directed to the internal IP address. Therefore, it enables an organization to logically separate the private and public multicast networks.

Multicast Service Reflection Working Architecture

For multicast service reflection, the virtual interface is configured to statically join the group that needs to be translated to build a multicast tree. The virtual interface maintains information about:

  • Input interface
  • Private-to-public multicast group mappings
  • Mask length to define the pool range
  • Source of translated packet

When a packet is forwarded to a virtual interface, it is reflected for translation. The source IP address is changed to the IP address of the virtual interface subnet, which prevents RPF failures. Finally, the destination IP address is translated to a new multicast group IP address.

Figure 73-1 shows the multicast service reflection working architecture.

Figure 73-1 Multicast Service Reflection Working Architecture

 

Restrictions for Multicast Service Reflection

Following restrictions apply for multicast service reflection feature:

  • The virtual interface should be installed on the border router.
  • Multicast service reflection does not support bidirectional multicast.
  • Protocol Independent Multicast (PIM)/IGMP control packets are not translated.
  • Multicast service reflection does not support P2P GRE tunnelling.
  • Multicast service reflection does not support IPv6 multicasting.
  • Only 1000 service reflection translations are supported.
  • Multicast service reflection is not supported in the PIM-Dense mode.

Configuring Multicast Service Reflection

Complete these steps to configure multicast service reflection feature.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip multicast-routing [ distributed ]

4. interface loopback loopback_id

5. description description

6. ip address ip_address subnet_mask

7. ip pim sparse-mode

8. exit

9. interface gigabitEthernet slot/port

10. ip address ip_address subnet_mask

11. ip pim sparse-mode

12. exit

13. interface gigabitEthernet slot/port

14. ip address ip_address subnet_mask

15. ip pim sparse-mode

16. exit

17. interface vif_id

18. ip address ip_address subnet_mask

19. ip pim sparse-mode

20. ip service reflect interface_id destination destination_ip1 to destination_ip2 mask-len subnet_mask_length source source_ip

21. ip igmp static-group {* | group-address [ source { source-address | ssm-map }]}

22. exit

23. ip pim rp-address rp_address

24. end

DETAILED STEPS

 

Command
Purpose

Step 1

enable

 
R1> enable

Enables the privileged EXEC mode. Enter your password if prompted.

Step 2

configure terminal

 

R1# configure terminal

Enters the global configuration mode.

Step 3

ip multicast-routing [ distributed ]

 

R1(config)# ip multicast-routing

Enables the IP multicast routing.

Step 4

interface loopback loopback_if_number

 

R1(config)# interface Loopback0

Enters the interface configuration mode.

Step 5

description description

 

R1(config-if)# description Rendezvous Point for Public Net

Describes the interface.

Step 6

ip address ip_address subnet_mask

 

R1(config-if)# ip address 22.22.22.22 255.255.255.255

Assigns the IP address and subnet mask to the interface.

Step 7

ip pim sparse-mode

 

R1(config-if)# ip pim sparse-mode

Enables the PIM sparse mode on the interface.

Step 8

exit

 

R1(config-if)# exit

 

Exits the interface configuration mode.

Step 9

interface gigabitethernet GigabitEthernet_interface_number

 

R1(config)# interface GigabitEthernet2/0/0

Enters the interface configuration mode.

Step 10

ip address ip_address subnet_mask

 

R1(config-if)# ip address 2.1.1.1 255.255.0.0

Assigns the IP address and subnet mask to the interface.

Step 11

ip pim sparse-mode

 

R1(config-if)# ip pim sparse-mode

Enables the PIM sparse mode on the interface.

Step 12

exit

 

R1(config-if)# exit

 

Exits the interface configuration mode.

Step 13

interface gigabitethernet GigabitEthernet_interface_number

 

R1(config)# interface GigabitEthernet4/13

Enters the interface configuration mode.

Step 14

ip address ip_address subnet_mask

 

R1(config-if)# ip address 23.1.1.2 255.255.0.0

Assigns the IP address and subnet mask to the interface.

Step 15

ip pim sparse-mode

 

R1(config-if)# ip pim sparse-mode

Enables the PIM sparse mode on the interface.

Step 16

exit

 

R1(config-if)# end

 

Exits the interface configuration mode.

Step 17

interface interface_name

 

R1(config)# interface Vif1

Enters the interface configuration mode.

Step 18

ip address ip_address subnet_mask

 

R1(config-if)# ip address 1.1.1.1 255.255.0.0

Assigns the IP address and subnet mask to the interface.

Step 19

ip pim sparse-mode

 

R1(config-if)# ip pim sparse-mode

Enables the PIM sparse mode on the interface.

Step 20

ip service reflect input-interface destination destination-address to new-destination-address mask-len number source new-source-address

 

R1(config-if)# ip service reflect GigabitEthernet2/0/0 destination 239.1.1.100 to 225.1.1.100 mask-len 32 source 1.1.1.2

Matches and rewrites the multicast packets routed onto the virtual interface.

  • The matched and rewritten packets are sent back into multicast packet routing (or unicast routing if the destination is unicast), where they are handled like any other packets arriving from an interface.

Step 21

ip igmp static-group {* | group-address [source {source-address | ssm-map}]}

 

R1(config-if)# ip igmp static-group 239.1.1.100

Configures the router to be a statically connected member of the specified group on the interface, and forwards traffic destined for the multicast group onto the interface.

Note This step is only applicable for multicast-to-multicast and multicast-to-unicast scenarios.

Step 22

exit

 

R1(config-if)# end

 

Exits the interface configuration mode.

Step 23

ip pim rp-address rp-address

 

R1(config)# ip pim rp-address 22.22.22.22

 

 

Configures the address of a PIM RP for a particular group.

Step 24

end

 

R1(config-controller)# end

 

 

Ends the configuration session.

Configuration Example

This example describes how to configure multicast service reflection.

R11>enable
R11#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R11(config)#ip multicast-routing
R11(config)#interface Loopback0
R11(config-if)#description Rendezvous Point for Public Net
R11(config-if)#ip address 22.22.22.22 255.255.255.255
R11(config-if)#ip pim sparse-mode

R11(config-if)#exit

R11(config)# interface GigabitEthernet2/0/0

R11(config-if)# ip address 2.1.1.1 255.255.0.0

R11(config-if)#ip pim sparse-mode

R11(config-if)#exit

R11(config)#interface GigabitEthernet4/13
R11(config-if)#ip address 23.1.1.2 255.255.0.0
R11(config-if)#ip pim sparse-mode

R11(config-if)#exit

R11(config)#interface Vif1
R11(config-if)#ip address 1.1.1.1 255.255.0.0
R11(config-if)#ip pim sparse-mode
R1(config-if)#ip service reflect GigabitEthernet2/0/0 destination 239.1.1.100 to 225.1.1.100 mask-len 32 source 1.1.1.2
R1(config-if)#ip igmp static-group 239.1.1.100
R1(config-if)#exit
R1(config)#ip pim rp-address 22.22.22.22

R1(config)#exit

For more information on configuring multicast service reflection, see Configuring Multicast Service Reflection.