Understanding EX8208 Switch Component and Functionality Redundancy
The Juniper Networks EX8208 Ethernet Switch is available as a fully redundant system. A redundant EX8208 switch configuration is designed so that no single point of failure can cause the entire switch to fail. See EX8208 Switch Configurations.
This topic describes:
Hardware Components That Provide Redundancy
The following hardware components provide redundancy to an EX8208 switch:
- SRE modules—An EX8208 switch can have either one
Switch Fabric and Routing Engine (SRE) module or two SRE modules.
If two SRE modules are installed, one SRE module functions as the
master and the other functions as the backup. If the master SRE module
fails or is removed the backup module takes over as the master SRE
module.
When the SRE modules are configured for graceful switchover, the backup SRE module automatically synchronizes its configuration and state with those of the master SRE module. Any update to the master SRE module is replicated on the backup SRE module. If the backup module assumes mastership, packet forwarding continues through the switch.
- Power supplies—You can install up to six AC or six
DC power supplies in an EX8208 switch. Each power supply connects
to the backplane of the chassis, which distributes the output power
produced by the power supplies to different switch components. (See Backplane in an EX8208 Switch.) Each
power supply provides power to all the components in the switch.
An N+1 power configuration is required for Juniper Networks EX8200 Ethernet Switches. In an N+1 power configuration, if one power supply fails or is removed, the remaining power supplies continue to supply power for the entire system without interruption. If dual power feed redundancy is required, the required power configuration is N+N. The DC power supplies provide independent A and B power feeds so that dual power redundancy is available even in an N+1 power configuration. See AC Power Supply in an EX8200 Switch and DC Power Supply in an EX8200 Switch.
- Cooling system—The cooling system in an EX8200 switch
consists of a single fan tray. The fan tray contains 12 fans. Under
normal operating conditions, the fans in the fan tray run at less
than full speed.
The fans are controlled by two fan tray controllers. The fans are numbered 1 through 12. Fans 1 through 6 are controlled by the first fan tray controller. Fans 7 through 12 are controlled by the second fan tray controller. If one fan tray controller fails, the other 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.
The fan tray continues to operate indefinitely and provides sufficient cooling even when a single fan fails provided the room temperature is within the operating range. See Cooling System and Airflow in an EX8208 Switch.
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 1 shows the available slots in the EX8208 chassis and the Routing Engine and control redundancy associated with different SRE module and Switch Fabric (SF) module combinations.
Table 1: Routing Engine and Control Redundancy for EX8208 Switches
Switch Fabric Redundancy
The switch fabric circuitry in an EX8208 switch is distributed across three modules—two SRE modules and one SF module. Any two of these three modules must be installed and functional to provide a working switch fabric with no redundancy. The third module, when present, provides partial redundancy (2+1) for the switching functionality, such that if any one of the two functional modules becomes nonoperational, the third module takes over.
Table 2 shows the available slots in an EX8208 chassis and the switch fabric redundancy associated with different SRE module and SF module combinations.
Table 2: Switch Fabric Redundancy for EX8208 Switches
