# Redundancy Features

This section describes system redundancy features.

## SRP Modules

| Note: This section applies to ERX7xx and ERX14xx models only. ERX310 routers contain one SRP module and therefore do not offer SRP module redundancy.

ERX7xx and ERX14xx models use a 1:1 redundancy scheme for the SRP module. When two SRP modules of the same type are installed in the chassis, one acts as a primary (active) and the second as a redundant (standby) module. Both SRP modules share a single SRP I/O module located in the rear of the chassis.

If the standby SRP module detects that the primary SRP module is not active (and high-availability mode is not enabled), it reboots the system and takes control. If high-availability mode has been enabled, automatic switchover occurs with near hitless failover. If you upgrade software, you must copy the software to the redundant SRP and reboot it. For information about configuring and managing SRP module redundancy, see JunosE System Basics Configuration Guide, Chapter 6, Managing Modules.

After you install two SRP modules, the modules negotiate for the primary role. A number of factors determine which module becomes the primary; however, preference is given to the module in the lower-numbered slot. The SRP modules record their latest roles and retain them the next time you switch on the system. For information about installing SRP modules, see Installing Modules.

### NVS Cards

If you have two SRP modules installed in a system, you can use NVS cards of different capacities on the SRP modules. The effective capacity of the higher-capacity NVS card will equal that of the lower-capacity NVS card. For information about installing NVS cards, see Installing Modules.

When you install new NVS cards or SRP modules, you must issue the synchronize command to match the file system of the NVS card on the redundant SRP module with the file system of the NVS card on the primary SRP module. (The NVS card on the redundant SRP module will hereafter be referred to as the redundant NVS card; the NVS card on the primary SRP module will hereafter be referred to as the primary NVS card.)

If the capacity of the primary NVS card is equal to or smaller than that of the redundant NVS card, the system copies all the files from the primary NVS card to the redundant NVS card. However, if the capacity of the primary NVS card exceeds that of the redundant NVS card, the system creates an invisible synchronization reserve file on the primary NVS card, provided that there is enough space for the file.

The purpose of the synchronization file is to prevent the creation of data that cannot fit on the redundant NVS card. The file contains no useful data, and is not visible when you view the files in NVS. The size of the file is equal to the difference in capacities of the two NVS cards. For example, if the primary NVS card has a capacity of 224 MB and the redundant NVS card has a capacity of 220 MB, the size of the synchronization file is 4 MB, and only 220 MB of space is available on the primary NVS card.

If the primary NVS card does not have enough space to create the synchronization reserve file, the synchronize command fails, and a warning message is displayed on the console. To resolve this issue, either delete unwanted files from the primary NVS card or replace the redundant NVS card with a higher-capacity NVS card.

## Line Modules

| Note: This section applies to ERX7xx and ERX14xx models only. ERX310 routers do not offer line module redundancy.

ERX7xx and ERX14xx models support line module redundancy for several line modules. For details about which line modules support redundancy, see the ERX Module Guide. In this scheme, an extra line module in a group of identical line modules provides redundancy in case of line module failure. To use this feature, you need a:

- Spare line module
- Redundancy midplane
- Redundancy I/O module

A redundancy midplane can cover 3–6 slots. It provides additional connectivity that enables the spare line module to take control of the I/O module associated with any failed line module in the redundancy group. The spare I/O module provides connectivity from the spare line module to the redundancy midplane.

The process by which the system switches to the spare line module is called switchover. When switchover occurs, the system:

1. Breaks the connection between the primary I/O module and the primary line module.
2. Connects the primary I/O module to the spare line module via the redundancy midplane and redundancy I/O module.

Protocol processing then takes place on the spare line module.

Figure 12 shows the data flow when a spare line module becomes active.

Figure 12: Data Flow When a Spare Line Module Is Active

For information about installing modules for line module redundancy, see Installing Modules. For information about configuring and managing SRP module redundancy, see JunosE System Basics Configuration Guide, Chapter 6, Managing Modules.

## Power

All E Series routers provide a power architecture that distributes redundant –48 VDC feeds through the router to each line module, SRP module, and fan module where DC-to-DC converters provide local conversion to the required secondary voltages.

The ERX310 router is available with either DC or AC power inputs. The AC-powered version can be configured with one or two hot-swappable power supplies for optional redundancy. (See Figure 5 and Figure 6.) The power supplies convert AC power to internal –48 V redundant DC feeds that are then distributed through the router.

## Fans

Forced air-cooling keeps the temperature of the E Series modules and components within normal operating limits. In ERX14xx models, six cooling fans are located in a tray at the top of the router (Figure 1). In ERX7xx models, four cooling fans are located in a tray on one side of the router (Figure 3). In the ERX310 router, two cooling fans are located in a tray on one side of the router (Figure 5).

The system monitors the temperature of each module. If the temperature of a module exceeds the maximum limit, the system immediately goes into thermal protection mode and the modules are powered off. The ERX system controller enters a low power mode, keeps the modules in a power-off condition, and does not respond to any management interface commands. For information about troubleshooting high operating temperatures, see Troubleshooting.

In ERX7xx and ERX14xx models, the fan tray has two redundant converters that power the fans (for the ERX14xx models, a –24 V, 50 W converter; for the ERX7xx models, a –12 V, 15 W converter). If one converter fails, the other takes over. The ERX310 router does not have redundant converters.

For all E Series routers, the system software reports an alarm if any of the fans or converters fail.