A Guide to Junos' Dual-RE and Dual-Fabric Systems

Juniper Networks' Junos operating system is renowned for its robustness and reliability. One of the key features that contribute to this reputation is its support for Dual Routing Engines (Dual-RE) and Dual-Fabric systems. This blog post will delve into these two features, providing a comprehensive guide for students studying for the JNCIS-ENT certification.

Dual Routing Engines (Dual-RE)

In a Junos device, the Routing Engine (RE) is the brain of the system. It runs the Junos OS, maintains the routing tables, and performs all the control plane functions. In a Dual-RE system, there are two REs: a primary (or active) RE and a backup (or standby) RE.

The primary RE is responsible for all the control plane functions, while the backup RE is in standby mode, ready to take over if the primary RE fails. This redundancy provides a high level of system availability and reliability.

Configuring Dual-RE

To configure Dual-RE, you need to set the redundancy-group under the chassis hierarchy. Here's an example:

user@router# set chassis redundancy-group 1 node 0 role primary
user@router# set chassis redundancy-group 1 node 1 role backup

In this example, node 0 is set as the primary RE and node 1 as the backup RE. The redundancy-group 1 is just an identifier for this redundancy group.

Dual-Fabric Systems

In addition to Dual-RE, Junos also supports Dual-Fabric systems for its modular chassis. The fabric is the data plane of the system, responsible for forwarding packets. In a Dual-Fabric system, there are two separate and independent fabrics. If one fabric fails, the other can take over, ensuring uninterrupted packet forwarding.

Configuring Dual-Fabric

To configure Dual-Fabric, you need to set the fabric redundancy-mode under the chassis hierarchy. Here's an example:

user@router# set chassis fabric redundancy-mode r-aps

In this example, r-aps is the redundancy mode, which stands for "Revertive Automatic Protection Switching". This mode means that when the primary fabric recovers after a failure, it will automatically switch back to being the primary fabric.


Dual-RE and Dual-Fabric are two powerful features of Junos that provide high system availability and reliability. They are essential topics for the JNCIS-ENT certification and understanding them will not only help you pass the exam but also become a better network engineer.

Remember, the key to mastering these topics is practice. So, get hands-on experience with Junos, try configuring Dual-RE and Dual-Fabric, and see how they work in real-world scenarios. Good luck with your studies!

© Ben Jacobson.RSS