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JUNOSe 9.1.x Multicast Routing Configuration Guide > Configuring IPv6 Multicast > Configuring Hardware Multicast Packet Replication

Configuring Hardware Multicast Packet Replication

You can configure IPv6 multicast to replicate packets to optimized hardware on a logical port instead of using the forwarding controller (FC) on the router.

The bandwidth between the line module and the I/O module or IOA on the E-series router is limited. A high-density Ethernet module provides eight physical ports that can consume the bandwidth between the line module and the I/O module or IOA before providing enough traffic to support egress line rate for all of these ports.

Figure 15 displays how multicast traffic is typically replicated on the line module. Each of these replicated packets is transmitted from the line module to the I/O module or IOA.


Figure 15: Packet Flow Without Hardware Multicast Packet Replication

The hardware multicast packet replication feature enables you to configure multicast traffic for a VLAN or S-VLAN to be replicated on the I/O module or IOA so that only one copy of the packet is transmitted from the line module to the I/O module or IOA. Replication for each of the ports is performed on the I/O module or IOA.

Configuring hardware multicast packet replication for high-density Ethernet is useful when you want to provide the same multicast stream out of some or all of the ports, such as for IP television (IPTV). Configuring hardware multicast packet replication enables you to:

You can use the feature to increase the bandwidth of multicast traffic out of each of the Gigabit Ethernet ports.

Figure 16 displays the flow of a multicast packet using the hardware multicast packet feature.


Figure 16: Packet Flow with Optimized Multicast Packet Replication

Each high-density Ethernet module has eight physical ports, numbered 0–7. A logical port is available for the hardware multicast packet replication feature, numbered port 8.

JUNOSe tracks the OIFs in an mroute that have been redirected to use the hardware multicast packet replication hardware. The system accepts only egress multicast traffic to traverse the interface stack on the enabled port. The system drops unicast traffic that is routed to this port.

Each port on the I/O module or IOA displayed in Figure 16 has two queues. These queues are further down the egress path than the queues found on the line module and populated by the FC.

The low-priority queue is dedicated to packets that are received from the line module queues that are dedicated to the physical ports. This queue blocks when full and provides backpressure to the line module. This queue services unicast and multicast traffic that is not using the hardware multicast packet replication feature.

The high-priority queue is dedicated to packets that are received from the line module queue for port 8. This queue is serviced at a higher priority than the first queue, and drops packets when full.

For more information about high-density Ethernet, see JUNOSe Physical Layer Configuration Guide, Chapter 5, Configuring Ethernet Interfaces.

Supported Modules and Encapsulations

You can enable optimized multicast packet replication on port 8 of the following high-density Ethernet modules:

When enabled, the optimized multicast packet replication feature defines the encapsulation of the egress multicast packet. The following encapsulations are supported:

The optimized multicast packet replication feature also provides an interface over which you can configure the following:

Relationship with OIF Mapping

Multicast OIF mapping enables the router to decrease the inefficiencies associated with replicating streams of multicast traffic. Using OIF maps, MLD joins that the router receives on a subscriber interface can be mapped to a special interface for forwarding.

The hardware multicast packet replication feature enables you to redirect each of the IPv6 interfaces on a line module over a dedicated multicast VLAN to a single IPv6 interface over port 8. The FC is only required to send a single packet per dedicated multicast VLAN to the I/O module or IOA. The module then replicates this packet to the appropriate ports.

For more information about configuring OIF mapping, see Configuring Group Outgoing Interface Mapping in Chapter 11, Configuring Multicast Listener Discovery.

Hardware Multicast Packet Replication Considerations

When configuring hardware multicast packet replication, the following considerations apply.

You cannot create the following configurations:

For the hardware multicast packet replication feature, you must attach policies to an interface stack over port 8 that defines the encapsulation of the egress multicast traffic. The system supports policies over port 8 just as it is above any of the other ports on this line module.

Policies applied to the interface stack over port 8 affect the packets traversing this stack whether or not the packet is destined for one port or all of the physical ports. Therefore, you cannot apply different egress policies to multicast traffic for the interfaces stacked above different ports, or rate limit on an individual interface over a port. You also cannot monitor policy statistics on individual interfaces over a port.

Instead, you can apply egress policy to an interface stacked over port 8. The system applies the policy before the packet has been elaborated for each of the ports.

For the hardware multicast packet replication feature, the FC does not replicate the packet for each of the individual ports. Instead, it places the packet on a special queue destined for port 8.

You can configure QoS on the packets flowing through port 8, but this has limited value because each packet passed through this port can be transmitted through one of more of the physical ports. Therefore, the packets placed on this special queue might not receive the same QoS behavior as ports 0–7.

We recommend that you configure the network so the I/O or IOA queues are not oversubscribed. The traffic transmitted by the physical port is a combination of packets from the two I/O or IOA queues. When the sum of the packets in these queues is greater than line rate, the system can drop traffic that is not using hardware multicast packet replication.

When you configure a traffic shaper on a physical port and configure hardware multicast packet replication, the packets created using the feature avoid the traffic shaper for that port. To control this, you can use traffic shaper on the physical port and port 8. The sum of the traffic shapers must be less than or equal to the line rate of the port.

A traffic shaper on port 8 can result in the overall utilization of egress bandwidth for any one port being less the line rate because the packets being replicated might not be transmitted to every port. Packets destined to some of the ports contribute to the traffic shaping for all of the ports on the I/O module or IOA.

Configuring Hardware Multicast Packet Replication

To configure hardware multicast packet replication:

  1. Configure port 8 on a high-density Ethernet module to accept redirected egress multicast traffic.
  1. Specify the Gigabit Ethernet interface on port 8.
  2. Create a VLAN major interface.
  3. Create a VLAN subinterface.
  4. Assign a VLAN ID.
  5. Configure an unnumbered IPv6 interface.
  6. Enable MLD on the interface with only multicast-data-forwarding capability.
    7. host1(config)#interface gigabitEthernet 2/8

    host1(config-if)#encapsulation vlan

    host1(config-if)#interface gigabitEthernet 2/8.1

    host1(config-if)#vlan id 1

    host1(config-if)#ipv6 unnumbered loopback 0

    host1(config-if)#ipv6 mld version passive
  1. Configure an IPv6 interface to redirect egress multicast traffic to port 8.
  1. Create a VLAN subinterface.
  2. Assign a VLAN ID.
  3. Assign an IPv6 address.
  4. Configure the interface to redirect egress multicast traffic to port 8.
    5. host1(config)#interface gigabitEthernet 2/0.101

    host1(config-if)#vlan id 1

    host1(config-if)#ipv6 address 1::1/64

    host1(config-if)#ipv6 multicast ioa-packet-replication gigabitEthernet 2/8.1

encapsulation vlan

ipv6 mld version

ipv6 multicast ioa-packet-replication

ipv6 unnumbered

Monitoring Optimized Multicast Packet Replication

This section describes how to monitor hardware multicast packet replication.

Port Statistics

Use the show interfaces gigabitEthernet command to display port statistics for port 8. For port 8, queue statistics have no direct relationship to any of the 8 ports because each packet transmitting through the queue can be sent through 1 or more of the 8 physical ports. For more information, see Monitoring Ethernet Interfaces in JUNOSe Physical Layer Configuration Guide, Chapter 5, Configuring Ethernet Interfaces.

IP and VLAN Statistics

Use the show vlan subinterface command to display statistics for a VLAN interface configured over port 8. For more information, see Monitoring Ethernet Interfaces in JUNOSe Physical Layer Configuration Guide, Chapter 5, Configuring Ethernet Interfaces.

Use the show ipv6 interface command to display statistics for an IPv6 interface configured over port 8. For more information, see Monitoring IPv6 in JUNOSe IP, IPv6, and IGP Configuration Guide, Chapter 2, Configuring IPv6.

Multicast traffic redirected by the hardware multicast packet replication feature is displayed in the statistics for the IPv6 or VLAN interface over port 8, not the original IP or VLAN interface over the physical port.

The statistics for the IPv6 or VLAN interface over port 8 reflect the number of packets that passed through this interface destined for the hardware multicast packet replication hardware. These statistics have no direct correlation to the number of packets being transmitted from any of the physical ports.

MLD Statistics

Use the show ipv6 mld interface command to display statistics, including hardware multicast packet replication status, for an IPv6 interface stacked over port 8. For more information, see Monitoring MLD in Chapter 11, Configuring Multicast Listener Discovery.

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