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    IPv6 Hardware Multicast Packet Replication Overview

    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 input/output adapter (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 1 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 1: Packet Flow Without Hardware Multicast Packet Replication

    Packet Flow Without Hardware Multicast
Packet Replication

    The hardware multicast packet replication feature enables you to configure multicast traffic for a virtual LAN (VLAN) or service VLAN (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:

    • Reduce the number of packets sent from the FC to the module.
    • Reduce the CPU consumed by the FC processing each elaboration of the packet.

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

    Figure 2 displays the flow of a multicast packet using the hardware multicast packet feature.

    Figure 2: Packet Flow with Optimized Multicast Packet Replication

    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 outgoing interfaces (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 2 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 Configuring Ethernet Interfaces in JunosE Physical Layer Configuration Guide.

    Supported Modules and Encapsulations

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

    • GE-8 I/O module (pairs with the GE-HDE line module)
    • ES2-S1 GE-8 IOA (pairs with the ES2 4G LM and the ES2 10G LM)

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

    • IPv6 over Gigabit Ethernet
    • IPv6 over VLAN
    • IPv6 over S-VLAN

      Note: 802.3ad link aggregation group (LAG) bundles do not support optimized multicast packet replication.

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

    • IP maximum transmission unit (MTU)
    • Ethernet MTU
    • Egress IP policy
    • Egress VLAN policy
    • QoS

    Relationship with OIF Mapping

    Multicast OIF mapping enables the router to decrease the inefficiencies associated with replicating streams of multicast traffic. Using OIF maps, Multicast Listener Discovery (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 MLD Group Outgoing Interface Mapping.

    Published: 2014-08-20