Packet Flow on the Multiservices PIC

Control traffic, which controls the data plane and interfaces with the Routing Engine, is processed with sockets, as it is on the Routing Engine.

Traffic is destined to or originates from the PIC interface’s address(es).

Data traffic, which processes packets, uses an internal library built on the Services SDK (formerly MP SDK) packet driver to obtain and send each packet; it does not use sockets to gain access to each packet. Services SDK applications can manipulate packets directly by calling zero-copy functions at line rate. The extent of parallel processing is controllable. The application can be considered a step on the packet processing pipeline.

Packet traffic is always from a Multiservices PIC, through the Packet Forwarding Engine, to another Multiservices PIC:


Packet Flow Overview

Packets are routed through the Multiservices PIC as follows:

  1. The customer packet arrives on an inbound PIC.

  2. For handling data, the application uses routes to direct the packet to a PIC interface.

    For control traffic, you must configure an IP address on the ms- interface. (This address can be externally visible; Network Address Translation is also an option.) The IP address you configure in turn translates into a route for that address, pointing to the PIC.

  3. The driver on the PIC delivers the packet to a control or data CPU.

    If the packet is a data packet, the packet loop running in the application's data component reads the packet from a FIFO queue and outputs it to another FIFO. Data packets also contain information about the incoming and outgoing VRF.

  4. The application sends traffic back to the driver indicating which ms- interface or routing table (vrf_id) to use. The driver forwards the traffic to the Packet Forwarding Engine.

  5. The Packet Forwarding Engine sends the packet out of the router.

Packet flow within the Multiservices PIC depends on whether the packet is going through a control or a data CPU.

Control CPU

An overview of control packet flow is as follows:


Control Packet Flow

Data CPU

An overview of data packet flow is as follows:


Data Packet Flow

Packet Steering

Packets can be steered towards a PIC in three ways:

You can also enable Multicast replication by configuring IGMP static joins to the PIC's IFL.

For additional details about creating routes and handling packets, see the following topics:

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