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Understanding the EX Series Redundant Power System

SUMMARY The Redundant Power System (RPS) provides backup power to a switch if the primary power source fails.

EX Series Redundant Power System Hardware Overview

You can use the EX Series Redundant Power System (RPS) to provide backup power for Juniper Networks EX2200 Ethernet Switches, (except Juniper Networks EX2200-C Ethernet Switches) and Juniper Networks EX3300 Ethernet Switches that are standalone switches or are members of a Virtual Chassis.

Most EX Series switches have a built-in capability for redundant power supplies—therefore, if one power supply fails on those switches, the other power supply takes over. However, EX2200 switches and EX3300 switches have only one internal fixed power supply. If an EX2200 switch or EX3300 switch is deployed in a critical situation, we recommend that you connect a an RPS to that switch to supply backup power during a loss of power.

RPS is not a primary power supply—it only provides backup power to switches when the single dedicated power supply fails. An RPS operates in parallel with the single dedicated power supplies of the switches connected to it and provides all connected switches enough power to support either Power over Ethernet (PoE) or non-PoE devices when the power supplies on the switches fail.

An RPS can hold up to three power supplies connected to as many as six switches—how that power is allocated is up to you. You determine whether or not to connect switches that provide PoE and you determine which switches have priority. Priority becomes an issue when you connect more than three switches that provide PoE to a fully loaded RPS because a switch providing PoE requires more power than a switch that does not provide PoE. Because a power supply can support only one switch providing PoE, the RPS can become oversubscribed when too many switches that must have enough power for PoE have a power failure.

Benefits of the EX Series Redundant Power System

Provides power backup—You connect up to six EX2200, EX3300, or a combination of these switches and supply power to any three of them.

Protection from high-voltage input and short circuits—RPS provides protection from high-voltage input and short circuits.

Switch Models and Configurations Supported by the RPS

The RPS supports all EX3300 switches and EX2200 switches except EX2200-C switches. You can simultaneously connect any supported switches to the same RPS, whether the switches are standalone switches or are configured in a Virtual Chassis.

All power provided by RPS is either PoE or non-PoE. By default, RPS supports switches that provide PoE. If even one switch provides PoE, then the RPS must be configured to provide enough power for PoE. When enough power for PoE is supplied, one switch can be powered by each power supply. If the switches are not providing PoE power, two switches can be powered by one RPS power supply—you can reconfigure an RPS to provide non-PoE power using a feature called multi-backup.

Table 1 lists some possible scenarios and RPS solutions. These examples assume that each RPS is fully loaded with three power supplies.

Table 1: Sample Requirements and RPS Solutions

Switches Requiring Backup

You need this RPS configuration:

Six switches that do not provide PoE to attached devices

One RPS can simultaneously provide power to all six switches if you change the power default to multi-backup—this indicates that no attached switch provides PoE to any devices.

One switch that provides PoE to other devices or two switches that do not provide PoE to any devices

One RPS will always back up all three switches, whether or not they provide PoE to connected devices. Leave the power at the default setting (no multi-backup) and let RPS determine that two switches need only minimum power and one switch provides PoE and therefore needs extra power. RPS automatically supplies the correct level of power.

One EX Series Virtual Chassis member that supplies PoE, one switch that supplies PoE, and one switch that does not supply PoE to any connected devices

One RPS will always back up all three switches. Leave the power default setting (no multi-backup) and let RPS determine that one switch needs only minimum power, one switch needs extra power because it supplies PoE, and the Virtual Chassis member also provides PoE to connected devices.

One switch that supplies PoE and five switches that do not supply PoE

You have two options.

Option 1—Use one RPS: Up to three switches that do or do not supply PoE can be backed up simultaneously. You can prioritize the six switches to determine which three are most important if all six fail at once. You must leave the power default setting (no multi-backup) because you have one switch that supplies PoE to attached devices and therefore requires more power.

Option 2—Use Two RPSs: In this case, you can connect three switches to each RPS and all switches will be backed up if they all fail at once. Alternatively, you can change the power default to multi-backup on one RPS and connect all five switches that do not supply PoE to that RPS, leaving the other RPS to back up the switch that supplies PoE.

EX Series Virtual Chassis

Use as many RPSs as needed to back up all members of the Virtual Chassis.

When a Switch’s Power Supply Fails

Because the power supplies for both EX3300 switches and EX2200 switches are internal, if the switch’s power supply fails, you must replace the switch. You should remove or replace a switch with a failed power supply as soon as possible.

Do not try to use an RPS as a primary power supply because an RPS cannot boot or reboot a switch. Each switch connected to the RPS must have its own dedicated power supply and must have booted up using the internal power supply.

If a switch is deployed in a large network center where RPS has a separate source of electricity than the switches it supports, the RPS supplies power when only the switch’s electricity fails. In this case, you would not have to replace the switch because the power supply is still functional. The switch will resume using its own internal power supply when electricity to the switch is restored.

Components of the RPS

Table 2 lists and describes the components of an RPS:

Table 2: Redundant Power System Components

Component

Value

Power supplies that can be installed

Up to three EX-PWR3-930-AC power supplies. One is included and additional power supplies must be ordered separately.

Switch connector ports on RPS

6 (2 per power supply)

Power cords(for connecting power supplies to the AC power source outlet)

Up to three power cords, one per power supply.

RPS cables(for connecting a switch to a power supply installed in the RPS)

6 (1 for each RPS-to-switch connection). One cable is supplied with the RPS. Additional cables must be ordered separately.

Understanding How Power Priority Is Determined and Set for Switches Connected to the EX Series Redundant Power System

The Redundant Power System (RPS) is designed to provide backup power to switches that lack built-in redundant power supplies. The RPS provides backup power to switches that either supply power over Ethernet (PoE), which require more power, or switches that do not supply PoE, which require less power. A power supply can either power one PoE device or two non-PoE devices. That means if an RPS is fully loaded with three power supplies, supports PoE switches, and more than three PoE switches have a power failure, some switches will not be powered. You can, however, determine which switches will be powered when an RPS is oversubscribed. When too many connected switches fail, the switches are given power based on their priority. Priority is also reconfigured when any power change takes place. For example, if three switches are already being backed up and another switch has a power failure, the RPS detects this, reconfigures the current top priorities, and allots power accordingly.

Default RPS Priority

While six non-PoE switches can all simultaneously be backed up with three power supplies, only three PoE switches can be backed up (because PoE uses more power). This means that an RPS with four or more PoE switches connected will have to select three of them for backup. You can determine priority by the connector positions you use to connect the switches. By default, an RPS assigns priority to switches based on their switch connector port location, with the leftmost port having the lowest priority and the rightmost port having the highest priority. If the PoE switches shown in Figure 1 all fail, the manufacturing, support, and finance switches will be backed up because they are connected to the rightmost connectors.

Figure 1: Default PoE Switch Priority Is Determined by Connector Port LocationDefault PoE Switch Priority Is Determined by Connector Port Location

Changing the Priority of Switches on an EX Series RPS

There is a way to alter the priority of PoE switches on an RPS without disconnecting the cables. You can optionally reconfigure any of the attached switches from their CLIs to establish a switch’s RPS priority—this CLI configuration overcomes the priority determined by the switch connector port location. Priority ranges from zero (off) to 1 (lowest) through 6 (highest). By default, all switches are configured to 1, the lowest priority. Let’s say that the sales switch is reconfigured from the switch’s CLI for priority 5 (second highest).

Now in Figure 2, with the sales switch configured for RPS 5 from the CLI, the highest priority changes to sales (because 5 is higher than 1), then manufacturing, and then support.

Figure 2: Switch Priority After CLI ConfigurationSwitch Priority After CLI Configuration

When assigning power priority to switches by using the CLI on the switch, keep these points in mind:

  • By default, all switches are assigned priority 1 (lowest) and derive precedence from the location of their connector port on the RPS, with the rightmost port having highest priority.

  • Priority 0 assigned from a switch CLI means that the RPS does not provide any backup power to the switch. Essentially, this turns off RPS support.

  • Priority 6 assigned from a switch CLI is the highest priority and priority 1 is the lowest priority.

  • The CLI command that assigns priority to EX2200 switches is slightly different from the CLI command that assigns priority to EX3300 switches because EX3300 switches can be configured as a Virtual Chassis.

  • If two or more switches are assigned the same priority value from the switches’ CLIs , then the power priority for those switches is determined by the RPS switch connector port location, with the ports to the right receiving priority.

  • If a single power supply is installed, the RPS can provide backup power to one switch out of all the switches connected to the RPS. If you do not need any PoE power backup on any switch, you can increase the number of supported switches to two per power supply. Switches connected to an RPS must be either all PoE or all non-PoE.

  • The RPS discontinues supplying backup power to a lower-priority switch if it detects a backup power need for a higher-priority switch at the same time.

See Also

Determining and Setting Priority for Switches Connected to an EX Series RPS

A Redundant Power System (RPS) provides backup power according to the RPS priority configured on the standalone EX Series switches or Virtual Chassis member switches connected to it. If all switches connected to the RPS are set to the default priority of 1, the priority is determined on the basis of the RPS port to which they are connected, with higher port numbers having the higher priorities.

The number of switches for which an RPS can provide backup power depends on whether the switches provide power over Ethernet (PoE).

  • PoE: A fully loaded RPS provides backup power to a maximum of three switches that are enabled for PoE—the result in this case is one switch powered per power supply. If more than three PoE-enabled switches are connected to the RPS and the RPS is already providing backup power to three switches when another switch's power supply fails, the RPS detects this and re-allots backup power as required. It would then stop providing backup power to a low-priority switch to provide backup power to a higher-priority switch.

  • Non-PoE: If you changed the RPS power setting to non-PoE with the command request redundant-power-system multi-backup, your RPS is configured to provide back up power to as many as six non-PoE switches on a fully loaded RPS. Each power supply can support two switches when the switches do not need enough power for PoE.

Note:

Before an RPS can back up a switch connected to it, the switch’s RPS status must be ARMED. There are two ways to determine whether a switch’s RPS status is ARMED—either check that the corresponding port LED on the RPS is lit and on steady or issue this command from the switch’s CLI: show chassis redundant-power-system.

This topic describes how to determine and set the power priority for a switch connected to an RPS.

Using RPS Default Configuration

No configuration is required on an RPS if you:

  • Plan to back up as many as six non-PoE switches

  • Back up three PoE switches with three RPS power supplies

  • Back up four or more PoE switches with RPS three power supplies and let the RPS port to which the switch is connected determine the priority

By default, an RPS assigns priority to switches on the basis of their switch connector port location, with the with higher port numbers having the higher priorities. By default, all switches are themselves configured with the same RPS priority (priority 1, the lowest), which is why priority is derived from the RPS connector port numbers.

Setting the EX Series RPS Priority for a Switch (CLI)

Each switch connected to RPS has an RPS priority value—that priority value determines which PoE switches receive power first from the RPS. By default, all switches are configured for priority 1 so priority is then determined by switch connector port location, left (lowest) to right (highest).

You can change the priority of a switch to 0 (off), or 1 (lowest) through 6 (highest) from the switch itself—this configuration takes precedence over switch connector port location.

To set or change the priority for a switch that does not support Virtual Chassis:

To set or change the priority for a switch that supports Virtual Chassis:

Where member is 0 for a switch that has never been configured in a Virtual Chassis.

See Also