Configure High Availability

Learn how to configure the High Availability feature on your MX204, MX301, MX304, MX10004, or MX10008 router.

High availability on a Juniper MX204, MX301, MX304, MX10004, or MX10008 router is configured by combining hardware redundancy, such as dual Routing Engines (REs), with software features like Graceful Routing Engine Switchover (GRES), Nonstop Active Routing (NSR), and Virtual Router Redundancy Protocol (VRRP) for interface-level failover.

If your Routing Engine configuration includes a backup-router statement or an inet6-backup-router statement, you can also use the destination statement to specify a subnet address or multiple subnet addresses for the backup router. Include destination subnets for the backup Routing Engine at the [edit system (backup-router | inet6-backup-router) address]hierarchy level.

Required Features

Graceful Routing Engine Switchover (GRES)
Nonstop Active Routing (NSR)
Graceful Restart (GR)

Enable Graceful Routing Engine Switchover

The graceful Routing Engine switchover (GRES) feature in Junos OS and Junos OS Evolved enables a device with redundant Routing Engines to continue forwarding packets even if one Routing Engine fails. GRES preserves interface and kernel information, and traffic is not interrupted. However, GRES does not preserve the control plane.

Both standard and restart signaling-based helper modes are enabled by default, irrespective of the graceful-restart configuration status on the routing device. Junos OS allows you to disable or enable the helper modes based on your requirements.

To configure the helper mode options for graceful restart:

To enable graceful restart, add the graceful-restart statement at the [edit routing-options] hierarchy level.

The helper modes, both standard and restart signaling-based, are enabled by default.
To disable one or both of the helper modes, add the helper-disable <both | restart-signaling | standard> statement at the [edit protocols ospf graceful-restart] hierarchy level.
- To disable both standard and restart signaling-based helper modes:
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- To disable only the restart signaling-based helper mode:

Enable Nonstop Active Routing (NSR)

Nonstop active routing (NSR) uses the same infrastructure as GRES to preserve interface and kernel information. However, NSR also saves routing protocol information by running the routing protocol process (rpd) on the backup Routing Engine. By saving this additional information, NSR is self-contained and does not rely on helper routers (or switches) to assist the routing platform in restoring routing protocol information. NSR is advantageous in networks in which neighbor routers (or switches) do not support graceful restart protocol extensions. As a result of this enhanced functionality, NSR is a natural replacement for graceful restart.

To enable NSR:

A recommeded additional setting:
After committing, verify NSR is enabled:

Enable Graceful Restart

With routing protocols, any service interruption requires that an affected router recalculate adjacencies with neighboring routers, restore routing table entries, and update other protocol-specific information. An unprotected restart of a router can result in forwarding delays, route flapping, wait times stemming from protocol reconvergence, and even dropped packets. Some benefits of graceful restart are uninterrupted packet forwarding and temporary suppression of all routing protocol updates. Graceful restart enables a router to pass through intermediate convergence states that are hidden from the rest of the network.