02: Junos Operating System Fundamentals

Junos OS Design and Architecture

Junos is built on a hardened version of FreeBSD or Linux, depending on version.

Running a single operating system network wide makes administering the network easier.

Junos has a modular software architecture; each process runs in its own memory space.

Version Numbering

Versions are numbered in the form m.nZb.s, where;

• m.n is the major, minor version
  • m is the last two digits of the year, e.g. 21
  • n is the quarter, e.g. 1
• Z is the release type
  • R is the most common release type
• b is the build number
• s is the spin number

Separation of Control and Forwarding Planes

The routing engine is based on x86 or PPC architecure. It runs protocol and management sotware processes. It maintains the routing table and forwarding table (RIB/FIB).

The packet forwarding engine (PFE) runs on separate hardware. It usually runs on ASICs for increased performance. The PFE receives the forwarding table frequently from the routing engine. The PFE forwards Layer 2 and Layer 3 packets according to the forwarding table from the RE. It also implements stateless firewall filters and CoS, according to instructions from the RE.

Junos Routing Devices

• ACX series fanless for outdoor deployment
• MX series for medium to large POPs
• PTX series service provider supercore
• SRX series services gateway

Junos Switching Devices

• EX series low to medium density for enterprise
• QFX series high performance for datacentre environments

Other Juniper Devices

• JATP (EoL)
• Juniper Secure Analytics (JSA) security appliance (physical or virtual)
• Juniper VPN
• NFX series CPE
• AP series wireless access points
• Mist Edge
• BT series

Software Products

• vSRX vitual security appliance
• vMX virtual router
• vQFX virtual switch (limited performance)
• cSRX simplified version of the SRX