JunOS SRX High Availability Concepts

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After getting some information about SRX HA basics let’s get into JunOS SRX High Availability Concepts. This will get you some clear picture about JunOS SRX High Availability Concepts. There are different parts in JunOS High Availibility.

JunOS SRX High Availability Concepts

Cluster ID

To configure the devices into HA, they must be first made member of the cluster. A cluster ID is an identifier to identify its members. The members or devices of the same cluster ID share or synchronize the information required. Similarly, while defining MAC address of the redundant interfaces cluster ID is used.

Node ID

When the devices are made member of the cluster they are now uniquely identified by node ID. Node ID is the unique identifier for member device. Generally Node ID 0 is the primary device and Node ID 1 is the secondary device or backup device.

Redundancy Groups

In redundancy group, more than one resource from different nodes is added to a particular redundancy group. In case of failure, corresponding resource in the redundancy group will take the initiative and pass the traffic. For any redundancy groups only one node will be the primary node and other node will be the backup. In redundancy group, control plane and forwarding plane are added. The redundancy group 0 is the default group and contains control plane only. The node that is master in redundancy group 0 will have active routing engine. The active RE controls and configures the data plane. The redundancy group 1 or greater contains forwarding plane. Different SRX platform have different number of redundancy group. A Redundant Ethernet Interface (Reth) is addeded to forwarding plane redundancy group. A Reth interface contains multiple physical interfaces from both nodes. The interface of active node will pass traffic whereas the interface of passive node will remain idle.


The SRX devices have two types of interfaces, Redundant Ethernet Interfaces (Reths) and local interfaces. The Reth interface contains one or more physical interface as member whereas the local interface is an interface which is not a member of Reth.

JunOS SRX High Availability Concepts

In the figure there is node 0 and node 1 in HA. Interface ge-0/0/0 and ge-5/0/0 is member of Reth 1 and Reth 1 is member of redundancy group 1. Both nodes share the same MAC address of Reth 1. So if node 0 fails for some reason the node 1 doesn’t have to relearn anything.

In HA the SRX also supports local interfaces. This gives you the flexibility to configure the HA in traditional way.

After knowing all the basics you should now learn about the different modes of SRX HA deployment and it’s differences.


  1. SRX High Availability Deployment Guide
  2. SRX High Availability Design Guide


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Bipin is a freelance Network and System Engineer with expertise on Cisco, Juniper, Microsoft, VMware, and other technologies. You can hire him on UpWork. Bipin enjoys writing articles and tutorials related to Network technologies. Some of his certifications are, MCSE:Messaging, JNCIP-SEC, JNCIS-ENT, and others.

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