RFC 3654 (rfc3654) - Page 2 of 18
Requirements for Separation of IP Control and Forwarding
Alternative Format: Original Text Document
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