The SCB performs four major functions:
•
Route lookups—The Internet Processor application-specific integrated circuit (ASIC)
on the SCB performs route lookups using the forwarding table stored in synchronous
SRAM (SSRAM). After performing the lookup, the Internet Processor informs the
backplane of the forwarding decision, and the backplane forwards the decision to the
appropriate outgoing interface.
•
System component monitoring—The SCB 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 the appropriate alarm.
•
Exception and control packet transfer—The Internet Processor ASIC on the SCB passes
exception packets to a microprocessor on the SCB, which processes almost all of them.
The remaining packets are sent to the Routing Engine for further processing. Any errors
originating in the Packet Forwarding Engine and detected by the SCB are sent to the
Routing Engine using SYSLOG messages.
•
FPC reset control—The SCB monitors the operation of the FPCs. If it detects errors in
an FPC, the SCB attempts to reset the FPC. After three unsuccessful resets, the SCB
takes the FPC offline and informs the Routing Engine. Other FPCs are unaffected, and
normal system operation continues.
The SCB occupies the center slot of the card cage, and is installed into the backplane
from the front of the chassis (see Figure 259 on page 493).
Figure 259: M40 Router SCB Location
The SCB is field-replaceable and hot-pluggable. You can remove and replace it without
powering down the system; however, this causes major impact to the system. While the
SCB is out of the router, route lookups, system component monitoring, exception and
control packet transfer, and FPC operation and reset control cannot occur.
When you replace the SCB, it is rebooted by flash EEPROM.
493Copyright © 2012, Juniper Networks, Inc.
Chapter 22: Monitoring the SCB
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