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fan tray controller keeps half the fans working. This allows the switch to continue to
operate normally as long as the remaining fans cool the chassis sufficiently.
Thefantraycontinuestooperateindefinitelyandprovidessufficientcoolingevenwhen
a single fan fails provided the room temperature is within the operating range. See
“Cooling System and Airflow in an EX8208 Switch” on page 53.
Routing Engine and Control Redundancy
Each SRE module contains switch fabric circuitry,Routing Engine circuitry,and switch
control and management circuitry. An EX8208 switch can have one SRE module or two
SRE modules. If a switch has two SRE modules, one functions as the master while the
other functions as a backup and is in standby mode. This provides the switch with full
redundancy (1+1) for Routing Engine and switch control functionality.
Table 3 on page 12 shows the available slots in the EX8208 chassis and the Routing
Engine and control redundancyassociatedwith different SRE moduleand Switch Fabric
(SF) module combinations.
Table 3: Routing Engine and Control Redundancy for EX8208 Switches
Routing Engine and
Control RedundancySlotSFSlotSRE1SlotSRE0SwitchConfiguration
NoSF moduleEmptySRE moduleBaseconfiguration
NoSF moduleSRE moduleEmptyBaseconfiguration
YesEmptySRE moduleSRE moduleUser-defined
configuration
YesSF moduleSRE moduleSRE moduleRedundant
configuration
Switch Fabric Redundancy
Theswitchfabriccircuitryin an EX8208 switchis distributedacrossthreemodules—two
SREmodulesandone SF module.Any two ofthese threemodulesmust beinstalledand
functionaltoprovideaworkingswitchfabricwithnoredundancy.Thethirdmodule,when
present, provides partial redundancy (2+1) for the switching functionality,such that if
anyone of thetwo functionalmodulesbecomesnonoperational,the third moduletakes
over.
Table 4 on page 12 shows the available slots in an EX8208 chassis and the switch fabric
redundancy associated with different SRE module and SF module combinations.
Table 4: Switch Fabric Redundancy for EX8208 Switches
Switch Fabric
RedundancySlotSFSlotSRE1SlotSRE0SwitchConfiguration
NoSF moduleEmptySRE moduleBaseconfiguration
Copyright ©2010,Juniper Networks,Inc.12
CompleteHardwareGuide forEX8208 EthernetSwitches