15.4.6 IPv4 Multicast in VRF [SL-L3A]

<Structure of this section>

(1) IPv4 multicast VRF

You can connect the Switch to multiple VPNs and use IPv4 multicast in each VPN. Configure VRF for each VPN and run IPv4 multicast in each VRF. You can set different rendezvous points, BSRs, timers, and SSM address ranges for VRF-based IPv4 multicasts.

The figure below shows an example configuration in which the Switch is connected to four VPNs.The settings on the Switch in this example are given in the table.

Figure 15-21: IPv4 Multicast in VRF

Table 15-14: Configuration information for the Switch
VPN	Operation Protocol	Loopback addresses	Rendezvous point (The values in parentheses are rendezvous point addresses)	SSM address
1	PIM-SM	1.1.1.1	Switch (1.1.1.1)	Not used
2	PIM-SM/ PIM-SSM	2.2.2.2	Switch (2.2.2.2)	232.0.0.0/8
3	PIM-SSM	2.2.2.2	No	232.10.0.0/16
4	PIM-SM	3.3.3.3	Router 4 (1.1.1.1)	Not used

(2) IPv4 multicast extranet

If an IPv4 multicast extranet is used, IPv4 multicast forwarding can be performed between VRFs. In addition, if IPv4 multicast route filtering is used, you can limit the range of group addresses used in the extranet and the VRFs for which forwarding requests from the downstream are permitted.

Note that a unicast route to the sender must exist in the unicast extranet to establish the shortest path from the last-hop-router.

The following figure shows the overview of IPv4 multicast extranet operation.

Figure 15-22: Summary of IPv4 Multicast Extranet Operation

(3) PIM-SM VRF gateways

To perform multicast communication by using the PIM-SM protocol, IPv4 multicast packets must be forwarded to the last-hop-router. If PIM-SM is used in an extranet environment, IPv4 multicast packets must also be forwarded to all the last-hop-routers in the VRFs.

Use a PIM-SM VRF gateway to enable the Switch to forward IPv4 multicast packets to the rendezvous point of each VRF.

The PIM-SM VRF gateway set in the VRF containing the sender (multicast server) operates as the last-hop-router for the specified group in the target VPN, and requests the rendezvous point to forward packets. Upon receiving IPv4 multicast packets from the rendezvous point, the gateway forwards the packets to the destination VRFs.

The PIM-SM VRF gateway in a destination VPN operates as the first-hop-router.The gateway encapsulates IPv4 multicast packets, and sends the encapsulated packets (called register packets) to the rendezvous point of each VRF. When a rendezvous point receives register packets, the rendezvous point decapsulates the packets and transfers the decapsulated IPv4 multicast packets to the last-hop-router the same way as in normal PIM-SM operation. Next, the shortest-path delivery tree from the last-hop-router to the sender is generated. At the same time, IPv4 multicast packets in the extranet are also forwarded by hardware.

As described above, use of PIM-SM VRF gateways allows a PIM-SM-based extranet to be created without changing the settings of any components other than the Switch. The following figure shows an overview of PIM-SM VRF gateway operation.

Figure 15-23: Summary of PIM-SM VRF Gateway Operation

(4) Notes on using IPv4 multicast extranet

(a) Two or more stages of VRF forwarding in the device

The IPv4 multicast extranet does not permit multi-level VRF forwarding with one device.

For an IPv4 multicast route of a VRF, the same VRF must be used from the upstream interfaces to the downstream interfaces. Any forwarding requests from upstream multicast routing information with a different VRF are ignored. When downstream interfaces of a multicast route use one VRF, and the VRF of an upstream interface is switched to another VRF, the downstream interfaces are detached from the target multicast route.

As indicated in the following figure, when there is a unicast route from VPN 3 to VPN 1 via VPN 2, host 1 in VPN 2 can receive IPv4 multicast packets from server 1 in VPN 1, but host 2 in VPN 3 cannot.

Figure 15-24: When IPv4 multicast extranet is used, VRF forwarding is prohibited in the switch.

(b) PIM-SM/PIM-SSM interconnect

If you want to use an IPv4 multicast extranet to perform multicast forwarding between VRFs, make sure that all group addresses used in the multicast forwarding use the same protocol (for IPv4 multicast VRFs, the group addresses to be used with PIM-SSM can be specified for each VRF).

In an IPv4 multicast extranet, multicast forwarding between different protocols is impossible. The figure below shows an example in which inter-VRF forwarding cannot be performed because the protocols do not match.The settings on the Switch in this example are given in the table that follows.

Figure 15-25: When IPv4 multicast extranet is used, forwarding cannot be performed due to inter-protocol mismatch between VRF

Table 15-15: Configuration information about the Switch
VPN	Operation protocol	Rendezvous point (The values in parentheses are rendezvous point addresses)	SSM address
1	PIM-SM	Switch (1.1.1.1)	Not used
2	PIM-SSM	No	232.0.0.0/8

G1:232.10.10.10

S1:10.10.10.10