RE, PFE, and FEB Oh My!

Last Session, I talked briefly about Juniper M and T router platforms. But, no router can be complete without the ability to forward packets to different networks and to perform what is affectionately called "best path selection."

Acronyms of the moment:

FEB: Forwarding Engine Board (M-Series, might also be listed as cFEB which is compact FEB)

Before we explore more about the M and T Series routing platforms, I thought it prudent to talk a bit about some of the components that comprise equipment that is part of the "backbone of the Internet."

The Routing Engine or RE has a few primary functions:

1. Manage packet forwarding though the use of the PFE (Packet forwarding engine)
2. Control JUNOS the router OS
3. Manage the command line interface or CLI
4. Maintain master packet forwarding table and route tables
5. Provide troubleshooting tools

A Note on the routing and forwarding tables...

The routing table in JUNOS is comprised of all protocols and all routes whether they are static or dynamic. The forwarding table provides "best routes" for best path selection.

"Oh to be Separated!"

All Juniper routing platforms no matter the series do have some things in common. In all platforms there is a clean separation between the RE or "control plane" as it is sometimes called and the "forwarding plane" which is the packet forwarding engine or PFE. Also, JUNOS provides a modular, single software train, feature rich OS that is easier to manage. Gone are the days of long lists of system images.

What this means to you: The ability to run debug and troubleshooting commands without bogging down a router!

Note: Packet forwarding is also called "process switching"

The information in the packet forwarding table is passed to the PFE and it pushes packets to the next hop address. So therein lies more separation between forwarding and control.

"In the Hardware...."

For the M-Series platform, the PFE is a collection of Application Specific Integrated Circuits or ASICs that are on cards placed into the router chassis. (It is similar to a line card.) We will talk more about the J-Series router in a later section.

So you are probably wondering where are my interfaces? Not to fear the Physical Interface Card is here or PIC! The PIC holds the interfaces you will plug into such as Ethernet or Serial just to name a few. The PIC as an ASIC that controls the layers 1 and 2 aspects of pushing and pulling data from the wire and framing. (The layers I am referring to are layers of the OSI model.)