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Configuring a Backup Router

 

To achieve network reachability while loading, configuring, and recovering the router or switch, but without installing a default route in the forwarding table, include the destination option, specifying an address that is reachable through the backup router. Specify the address in the format network/mask-length. Both IPv4 and IPv6 addresses are supported.

If you have a backup router configuration in which multiple static routes point to a gateway from the management Ethernet interface, you must configure prefixes that are more specific than the static routes or include the retain option at the [edit routing-options static route] hierarchy level.

For example, if you configure the static route 172.16.0.0/12 from the management Ethernet interface for management purposes, you must specify the backup router configuration as follows:

Any destinations defined by the backup router are not visible in the routing table. They are only visible in the local forwarding table when the routing protocol process is not running. Therefore, a recommended best practice is to include the destinations of the backup router configured as static routes with the retain option. The retain option is necessary to allow the static route to remain in the forwarding table when the routing protocol process stops running, because the routing table does not exist if the routing protocol process is not running.

Also, the destination prefix under backup-router configuration cannot overlap with the destination prefix learned from routing protocol process (rpd).

On systems with dual redundant Routing Engines, the backup Routing Engine's reachability through the private management interface is based only on the functionality of the backup-router configuration. It is not based on whether the routing protocol process is running. On both Routing Engines, the backup-router statement adds the destination prefix upon bootup. On the master Routing Engine, a static route requires the routing protocol process to be running first before installing the destination prefix to the routing and forwarding tables.

Due to a system limitation, do not configure the destination address specified in the backup-router as 0.0.0.0/0 or ::/0. The mask has to be a nonzero value.

Active routes and more specific routes take precedence over destination prefixes defined with the backup-router statement.

Configuring a Backup Router Running IPv4 for Routers

In the example shown in Figure 1, the backup router is the default gateway of the management network.

As required, the backup router address is reachable and directly connected to the management interfaces on the two routing devices (fxp0 and me0).

Figure 1: Backup Router Sample Topology
Backup Router Sample
Topology

Optionally, instead of configuring the backup router at the [edit system] hierarchy level, you can use a configuration group, as shown in this procedure. This is a recommended best practice for configuring the backup router, especially if the device has dual Routing Engines. This procedure uses groups called re0 and re1 as an example.

To configure a backup router running IPv4:

  1. Include the backup-router statement at the [edit system] hierarchy level.

    For example:

  2. (Optional) Configure a static route to the management network.

    Junos OS only uses the backup router during the boot sequence. If you want to configure a backup router for use after startup, you can set up a static route. The static route goes into effect when the routing protocol process is running.

  3. If you used one or more configuration groups, apply the configuration groups, substituting the appropriate group names.

    For example:

  4. Commit the changes:

Configuring a Backup Router Running IPv6 for Routers

To configure a backup router running IPv6:

  1. Include the inet6-backup-router statement at the [edit system] hierarchy level.

    For example:



  2. (Optional) Configure a static route to the management network.

    Junos OS only uses the backup router during the boot sequence. If you want to configure a backup router for use after startup, you can set up a static route. The static route goes into effect when the routing protocol process is running.

  3. If you used one or more configuration groups, apply the configuration groups, substituting the appropriate group names.

    For example:

  4. Commit the changes:

Configuring a Backup Router for SRX Series Devices

This procedure describes how to manage two SRX Series devices in a chassis cluster mode using a backup router configuration, via fxp0.

The backup router address is reachable and directly connected to the management interfaces on the SRX chassis cluster (fxp0).

When you configure the backup router for SRX Series devices in chassis cluster mode, the backup router configuration is intended to facilitate the management access on the backup node only. The access to the primary node is enabled via the routing on the primary node. When the backup router configuration is done, a route is injected into the forwarding table on the secondary node. It is not possible to see the routing table on the secondary, as the routing subsystem does not run on the secondary. This example uses groups node 0 and node1.

  1. Include the backup-router statement at the [edit system] hierarchy level.

    To configure this section of the example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

  2. Commit the changes: