Configuring Hardware Multicast Packet Replication

Figure 4: 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:

• 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 additional bandwidth to increase the bandwidth of multicast traffic out of each of the Gigabit Ethernet ports.

Figure 5 displays the flow of a multicast packet using the hardware multicast packet feature.

Figure 5: Packet Flow with Hardware 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 5 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 the JunosE Physical Layer Configuration Guide.

Supported Modules and Encapsulations

You can enable hardware 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 hardware multicast packet replication feature defines the encapsulation of the egress multicast packet. The following encapsulations are supported:

• IPv4 over Gigabit Ethernet
• IPv4 over VLAN
• IPv4 over S-VLAN

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

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

• IP 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, IGMP joins that the router receives on a subscriber interface can be mapped to a dedicated multicast VLAN.

The hardware multicast packet replication feature enables you to redirect each of the IP interfaces on a line module over a dedicated multicast VLAN to a single IP 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 Configuring IGMP .

Hardware Multicast Packet Replication Considerations

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

• Do not configure or transmit routing protocols over port 8. The FC drops traffic routed to an IP interface stacked over port 8.
• We recommend that you configure the IP address of the IP interface over port 8 to be unnumbered.
• We recommend that you configure an IP interface over a VLAN over one of the physical ports to reference the IP interface over the same VLAN over port 8.

  You cannot create the following configurations:

  • When two IP interfaces configured over a port reference the same IP interface over port 8. The system does not accept this configuration attempt because you typically configure the hardware multicast packet replication feature to redirect multicast traffic over one VLAN, then redirect it to the same VLAN on port 8.
  • When the IP interface configured with the hardware multicast packet replication attribute is not installed on a line module that supports hardware multicast packet replication.
  • When the IP interface designated by the hardware multicast packet replication attribute is not installed on a line module that supports hardware multicast packet replication.
  • When the IP interface designated by the hardware multicast packet replication attribute is not on the same line module as the IP interface configured with this attribute.
• When you configure a unique source MAC address for VLANs on port 8, the hardware multicast packet replication hardware stamps the source MAC address on the VLAN, overwriting any MAC address that you configured. For more information, see Configuring Ethernet Interfaces in the JunosE Physical Layer Configuration Guide.
• The regular multicast implementation utilizes interface stacking that provides a unique IP attachment point for each elaboration of the egress multicast packet.

  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.

• The JunosE QoS component provides hierarchical egress scheduling and shaping on Gigabit Ethernet ports 0–7. The regular multicast implementation replicates packets on the FC, with each replicated packet placed on a line module queue destined for a single physical port. The line module queue can also receive QoS behavior specific to that queue.

  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 IP interface.
   6. Enable IGMP on the interface with only multicast-data-forwarding capability.
      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)#ip unnumbered loopback 0 host1(config-if)#ip igmp version passive
2. Configure an IP interface to redirect egress multicast traffic to port 8.
   1. Create a VLAN subinterface.
   2. Assign a VLAN ID.
   3. Assign an IP address.
   4. Configure the interface to redirect egress multicast traffic to port 8.
      host1(config)#interface gigabitEthernet 2/0.101 host1(config-if)#vlan id 1 host1(config-if)#ip address 10.1.1.1 255.255.255.0 host1(config-if)#ip multicast ioa-packet-replication gigabitEthernet 2/8.1

Configuring Hardware Multicast Packet Replication with OIF-Mapping

This section describes how to configure hardware multicast packet replication with OIF-mapping.

1. Configure port 8 on a supported high-density Ethernet module to accept redirected egress multicast traffic. For the procedure see Configuring Hardware Multicast Packet Replication. For information about supported high-density Ethernet modules see Supported Modules and Encapsulations.
2. Use OIF maps to map the subscriber IGMP interfaces (C-VLANs) to the dedicated multicast VLAN (M-VLAN). The dedicated M-VLAN should be located on the line module containing the IOA replication interface. The C-VLAN and M-VLAN can either be on the same or different line modules. For information about configuring OIF mapping see Configuring Group Outgoing Interface Mapping.
3. Configure the dedicated M-VLAN to redirect egress multicast traffic to port 8. For the procedure see Configuring Hardware Multicast Packet Replication.

Monitoring Hardware 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 the JunosE Physical Layer Configuration Guide.

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 the JunosE Physical Layer Configuration Guide.

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

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

The statistics for the IP 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.

IGMP Statistics

Use the show ip igmp interface command to display statistics, including hardware multicast packet replication configuration, for an IP interface stacked over port 8. For more information, see Monitoring IGMP in Configuring IGMP .