Juniper Junos OS: the essentials for network engineers

April 15, 2026·3 min read·442 words

Junos OS is Juniper Networks' proprietary operating system, used across all its platforms (EX, QFX, MX, SRX, PTX, ACX). It is renowned for its stability, commit-based model, YAML-like hierarchy and powerful automation capabilities (NETCONF, PyEZ). Guide to Junos essentials for 2026.

CLI modes

Operational mode (>): show, ping, traceroute and monitor commands
Configuration mode (#): edit the configuration using configure or edit
configure exclusive: lock the configuration to prevent conflicts
configure private: private branch with an atomic commit

Basic configuration

set system host-name SW-PARIS-01
set system root-authentication plain-text-password
set system services ssh root-login deny
set system login user admin class super-user authentication plain-text-password
set system ntp server 192.0.2.1
commit check: validate without applying
commit confirmed 10: commit with automatic rollback if not confirmed

VLANs and interfaces

set vlans DATA vlan-id 10
set interfaces ge-0/0/1 unit 0 family ethernet-switching port-mode access
set interfaces ge-0/0/1 unit 0 family ethernet-switching vlan members DATA
set interfaces ge-0/0/24 unit 0 family ethernet-switching port-mode trunk
set interfaces ge-0/0/24 unit 0 family ethernet-switching vlan members all
set interfaces irb unit 10 family inet address 192.168.10.1/24: L3 SVI

Routing

set routing-options static route 0.0.0.0/0 next-hop 192.168.1.254
set protocols ospf area 0 interface ge-0/0/24
set protocols bgp group EXT neighbor 10.0.0.2 peer-as 65002
show route: routing table
show route protocol bgp: BGP routes

Firewall filters (ACLs)

set firewall family inet filter BLOCK-TELNET term 1 from protocol tcp destination-port 23 then discard
set firewall family inet filter BLOCK-TELNET term 2 then accept
set interfaces ge-0/0/1 unit 0 family inet filter input BLOCK-TELNET

Virtual Chassis (Juniper stacking)

request virtual-chassis mode network-port: enable VC uplink ports
set virtual-chassis member 1 mastership-priority 255
set virtual-chassis member 2 mastership-priority 254
show virtual-chassis: stack status

Automation and APIs

NETCONF over SSH 830: set system services netconf ssh
PyEZ: Juniper Python library
Ansible modules: juniper.junos collection
Terraform provider: Juniper Junos
Mist API: REST cloud orchestration

Advanced rollback and commit

show system rollback compare 0 1: diff between 2 versions
rollback 5 ; commit: revert to the 5th previous configuration
load replace terminal: replace the configuration from pasted input
load merge: merge configurations

Junos vs Cisco IOS: key differences

Commit-based vs immediate: Junos buffers changes, while IOS applies them directly
Hierarchical set/delete commands vs configuration blocks
Native atomic rollback vs manual backup on IOS
Interface naming: ge-0/0/1 (Gigabit Ethernet slot 0 PIC 0 port 1) vs Gi1/0/1
No shutdown is implicit by default on Juniper
Junos commonly remains stable for 3-5 years, while IOS receives more frequent monthly updates

Order from OPTINOC

All Juniper equipment (EX, QFX, MX, SRX) supplied brand-new and genuine with Junos Care support. Free Junos essentials training for OPTINOC customers. Multi-site quote within 48 hours.