Forwarding Engine Board (FEB)

The Forwarding Engine Board (FEB) performs route lookup, filtering, and switching on incoming data packets, then directs outbound packets to the appropriate FPC for transmission to the network. It can process 40 million packets per second (Mpps).

The FEB installs into the midplane from the rear of the chassis, as shown in Figure 3. It weighs approximately 7 lb (3.2 kg). The FEB is field-replaceable, but you must power down the router before removing it from the chassis. Packet forwarding halts until the FEB is replaced, the router is powered on, and the Routing Engine finishes booting.

For FEB replacement instructions, see Replace the FEB.

The FEB communicates with the Routing Engine using a dedicated 100-Mbps Fast Ethernet link that transfers routing table data from the Routing Engine to the forwarding table in the Internet Processor II ASIC. The link is also used to transfer from the FEB to the Routing Engine routing link-state updates and other packets destined for the router that have been received through the router interfaces.

The ASICs and other components on the FEB provide the following functions:

• Route lookups—The Internet Processor II ASIC on each FEB performs route lookups using the forwarding table stored in SSRAM.
• Creation and reassembly of data cells—The I/O Manager ASIC divides incoming packets into 64-byte data cells for easier processing, and reassembles the cells for each packet after the forwarding decision is made for it. There is one I/O Manager ASIC on the M5 router and two on the M10 router.
• Management of memory on the FEB—One Distributed Buffer Manager ASIC receives the 64-byte data cells into which the I/O Manager ASIC divides incoming packets, and uniformly allocates the cells throughout the memory buffers on the FEB.
• Transfer of outgoing data packets—The second Distributed Buffer Manager ASIC passes notification of the forwarding decision for each packet to an I/O Manager ASIC so that data cells for the outgoing packet can be reassembled for transmission to the network.
• Transfer of exception and control packets—The Internet Processor II ASIC passes exception packets to the microprocessor on the FEB, which processes almost all of them. The FEB sends any remaining exception packets to the Routing Engine for further processing. When the FEB detects an error originating in the Packet Forwarding Engine, it sends it to the Routing Engine using system logging (syslog) messages.
• Monitoring of system components—The FEB monitors other system components for failure and alarm conditions. It collects statistics from all sensors in the system and relays them to the Routing Engine, which sets alarms as appropriate. For example, if the temperature of a component exceeds the lower of two internally defined thresholds, the Routing Engine issues a “high temperature” alarm. If the temperature exceeds the higher threshold, the Routing Engine initiates a system shutdown.
• Providing SONET/SDH clock source—The FEB generates a 19.44-MHz clock signal for use by SONET/SDH interfaces.

FEB Components

An FEB has the following components (see Figure 5):

• I/O Manager ASIC (one on the M5 router and two on the M10 router)—Divide incoming packets into 64-byte data cells for easier processing, and reassemble the cells for each packet after the forwarding decision is made for it.
• Two Distributed Buffer Manager ASICs—Process incoming and outgoing packets: one distributes data cells (which the I/O Manager ASIC derives from incoming packets) to the memory buffers on the FEB, while the second forwards notification of routing decisions to an I/O Manager ASIC.
• One Internet Processor II ASIC—Performs route lookups and makes routing decisions.
• Parity-protected synchronous SRAM (SSRAM)—Stores the forwarding table.
• Processor subsystem—Manages FEB functions and handles exception packets. The processor has the following components:
  • One PowerPC 603e processor
  • Parity-protected Level 2 cache
  • Parity-protected DRAM
• EEPROM—Stores the serial number and revision level.
• 19.44-MHz stratum 3 reference clock—Generates clock signal for SONET/SDH PICs.
• I²C controller—Monitors the status of router components.
• Ejector levers—Control the locking system that secures the FEB in the chassis.

For specific information about FEB components (for example, the amount of DRAM), issue the show chassis feb command.

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