Network operating system comparer

Junos OS

Vendor

Juniper

First shipped

7 July 1998

Lineage

FreeBSD 4, 32-bit → FreeBSD 10, 64-bit from Release 15.1 → ScreenOS security folded in after the NetScreen acquisition → Junos OS Evolved on Linux

What it runs on

FreeBSD. Because that is a Unix, there is a real Unix shell underneath with the ordinary Unix tools available.

How state is shared

Routing Engine centric: the RE holds the control plane and the Packet Forwarding Engine does the forwarding, with a defined boundary between them. Daemons are separate processes.

Control and forwarding

The RE/PFE split is the design's organising idea, and it is why the control plane can be rebuilt or fail over while forwarding continues.

How changes are applied

Candidate and commit, with rollback and configuration comparison built in. This was Junos's signature from the beginning and much of the industry has since followed.

What an upgrade costs

Unified releases across the portfolio; in-service upgrade on supported platforms.

The distinguishing idea

One operating system, one source tree, across routing, switching and security. The consistency is the product as much as any individual feature.

Strengths

• The commit model, with rollback and a readable diff before anything is applied.
• A single consistent operating system across very different hardware.
• A genuine Unix underneath, so ordinary tools and scripting are available.

Weaknesses

• The configuration hierarchy is unfamiliar to engineers arriving from an IOS-shaped world, and the transition takes real effort.
• Two architectures now coexist - FreeBSD-based Junos and Linux-based Junos Evolved - and knowing which one is in front of you matters.