RFC 3654 (rfc3654) - Page 2 of 18

Requirements for Separation of IP Control and Forwarding

RFC 3654                  ForCES Requirements              November 2003


1. Introduction

   An IP network element is composed of numerous logically separate
   entities that cooperate to provide a given functionality (such as a
   routing or IP switching) and yet appear as a normal integrated
   network element to external entities.  Two primary types of network
   element components exist: control-plane components and forwarding-
   plane components.  In general, forwarding-plane components are ASIC,
   network-processor, or general-purpose processor-based devices that
   handle all data path operations.  Conversely, control-plane
   components are typically based on general-purpose processors that
   provide control functionality such as the processing of routing or
   signaling protocols.  A standard set of mechanisms for connecting
   these components provides increased scalability and allows the
   control and forwarding planes to evolve independently, thus promoting
   faster innovation.

   For the purpose of illustration, let us consider the architecture of
   a router to illustrate the concept of separate control and forwarding
   planes.  The architecture of a router is composed of two main parts.
   These components, while inter-related, perform functions that are
   largely independent of each other.  At the bottom is the forwarding
   path that operates in the data-forwarding plane and is responsible
   for per-packet processing and forwarding.  Above the forwarding plane
   is the network operating system that is responsible for operations in
   the control plane.  In the case of a router or switch, the network
   operating system runs routing, signaling and control protocols (e.g.,
   RIP, OSPF and RSVP) and dictates the forwarding behavior by
   manipulating forwarding tables, per-flow QoS tables and access
   control lists.  Typically, the architecture of these devices combines
   all of this functionality into a single functional whole with respect
   to external entities.

2. Definitions

   Addressable Entity (AE) - A physical device that is directly
   addressable given some interconnect technology.  For example, on IP
   networks, it is a device to which we can communicate using an IP
   address; and on a switch fabric, it is a device to which we can
   communicate using a switch fabric port number.

   Physical Forwarding Element (PFE) - An AE that includes hardware used
   to provide per-packet processing and handling.  This hardware may
   consist of (but is not limited to) network processors, ASIC's, line
   cards with multiple chips or stand alone box with general-purpose
   processors.





Khosravi & Anderson          Informational