SFM Slots
One or two SFMs can be installed into the midplane from the rear of the chassis, as shown
in “M40e Chassis Description” on page 8. Only one SFM is active at a time, with the
optional second SFM in standby mode. By default, the SFM in slot
SFM 0
is active. To
modify the default, include the appropriate
sfm
statement at the
[edit chassis redundancy]
hierarchy level of the configuration, as described in the section about SFM redundancy
in the
Junos OS System Basics Configuration Guide
.
SFM Redundancy
SFMs are hot-pluggable, as described in “M40e Field-Replaceable Units (FRUs)” on
page 157. Removing the standby SFM has no effect on router function. If the active SFM
fails or is removed from the chassis, the effect depends on how many SFMs are installed:
•
One SFM—Forwarding halts until the SFM is replaced and functioning again. It takes
approximately one minute for the replaced SFM to boot and become active; reading
in router configuration information can take additional time, depending on the
complexity of the configuration.
•
Two redundant SFMs—The effect depends on which release of the Junos OS is running
on the router:
•
With Junos OS Release 5.4 and later, the standby SFM assumes forwarding functions
in less than one second.
•
With Junos OS Release 5.3 and earlier, forwarding halts while the standby SFM boots
and becomes active, which takes approximately one minute; synchronizing router
configuration information can take additional time, depending on the complexity of
the configuration.
SFM Function
The SFM communicates with the Routing Engine using a dedicated 100-Mbps Fast
Ethernet link. The link transfers:
•
Routing table data from the Routing Engine to the forwarding table in the Internet
Processor II ASIC.
•
Routing link-state updates and other packets destined for the router that have been
received through the router interfaces from the SFM to the Routing Engine.
The ASICs and other components on the SFM provide the functions:
•
Route lookups—The Internet Processor II ASIC on each SFM performs route lookups
using the forwarding table stored in SSRAM.
•
Management of shared memory on the FPCs—One Distributed Buffer Manager ASIC
receives the 64-byte data cells into which the active I/O Manager ASIC on each FPC
divides incoming packets, and uniformly allocates them throughout the shared memory
buffers located on the FPCs.
21
Copyright © 2010, Juniper Networks, Inc.
Chapter 2: M40e Hardware Components
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